On the origin of emission and thermal quenching of SRSO:Er 3+ films grown by ECR-PECVD

Artur Podhorodecki
Grzegorz Zatryb
Lukasz W Golacki
Jan Misiewicz
Jacek Wojcik
Peter Mascher
On the origin of emission and thermal quenching of SRSO:Er 3+ films grown by ECR-PECVD
N A N O E X P R E S SSiliconNanocrystalsErbiumEmissionQuenchingTemperaturePhotoluminescence PACS codes: 7867Bf7363Bd7840Fy7855Ap Background
Silicon nanocrystals embedded in a silicon-rich silicon oxide matrix doped with Er 3+ ions have been fabricated by electron cyclotron resonance plasma-enhanced chemical vapor deposition. Indirect excitation of erbium photoluminescence via silicon nanocrystals has been investigated. Temperature quenching of the photoluminescence originating from the silicon nanocrystals and the erbium ions has been observed. Activation energies of the thermally activated quenching process were estimated for different excitation wavelengths. The temperature quenching mechanism of the emission is discussed. Also, the origin of visible emission and kinetic properties of Er-related emission have been discussed in details.

Background

Rare-earth-doped materials have been investigated for a number of years in order to develop practical light sources for photonic applications. A silicon-rich silicon oxide (SRSO) matrix seems to be very promising as an efficient photosensitizer for different rare-earth (RE) ions such as: Nd 3+ [1,2], Tb 3+ [3], or Er 3+ [4,5]. Among these ions, the Er 3+ ion is well known as an alternative to epitaxially grown light sources emitting in the third telecommunication window [6,7]. One of the advantages of a SRSO matrix as a host for RE ions is the formation of Si nanocrystals (Si-NCs) within the matrix which could participate in indirect excitation of Er 3+ ions via an energy transfer process. Additionally, these clusters can improve the film's conductivity, which in practice can be an even more important benefit. The advantage of using Si-NCs comes from their high absorption cross section (σ abs ) as compared to very low ones for most of the RE ions. For example, for erbium in SiO 2 , the experimentally determined value of σ abs is 8 × 10 −21 cm 2 [8], while for Si-NCs at 488 nm, this value is equal to 10 −16 cm 2 [9]. Moreover, Franzo et al. [10] and Gourbilleau et al. [11] reported already that amorphous Si nanoclusters (aSi-NCs) can be sufficient and even better sensitizers than Si-NCs, enhancing the optical activity of Er 3+ ions. Thus, enriching SiO 2 with Si nanocrystals or amorphous nanoclusters should significantly increase Er 3+ emission due to their indirect excitation. However, to date, achieving gain from this material has proven to be a notoriously difficult task. This is, in part, due to the low excitable Er 3+ fraction sensitized through the Si-NCs (0.5% to 3% [12,13]) and the low number of excitable Er 3+ ions per nanocrystal (1 to 2 [14,15] or 20 [12]), which affects the maximum gain that can be achieved in a Si-sensitized gain medium. It is believed that the low number of optically active Er 3+ ions coupled to Si-NCs is due to processes like fast Auger back-transfer from excited Er 3+ ions to excitons in Si-NCs, excited-state absorption, or Er 3+ pair-induced quenching. Nevertheless, experimental data strengthening or excluding any of these explanations is still limited. One of the exceptions is recent work of Navarro-Urrios et al. [16] who have shown that none of these processes are responsible for the low fraction of Er 3+ coupled to Si-NCs, and only the short range of interaction between Si-NCs and Er 3+ (0.5 nm) is the main limitation to achieving a high fraction of ions coupled to Si-NCs. As a consequence, it has been shown that the amount of excitable Er 3+ depends strongly on the Si-NC density as only those Er 3+ ions in close proximity to the Si-NCs are being excited [17]. Therefore, it is believed that the main limitation on obtaining gain in such a system is the low density of sensitizers, the short range of the Si-NCs and Er 3+ interaction [13], and low solubility of Er 3+ ions in SRSO matrix.

However, in addition to weak Si-NCs-Er 3+ coupling, reduction in Er 3+ emission efficiency can also be due to many quenching processes accompanying the excitation and recombination of Er 3+ ions. Such processes still have not been widely investigated. Furthermore, even today, the detailed excitation mechanism of Er 3+ ions in SRSO is still not well understood. Investigations of timeresolved photoluminescence of Er 3+ ions in SRSO reveal two major excitation mechanisms leading to 1.5-μm emission, distinguishable by their dynamics: a fast relaxation within the Si-NCs and energy transfer to ions (<100 ns), taking Er 3+ ions directly to the first excited state, and a slow relaxation and energy transfer, exciting Er 3+ ions to higher states. In both cases, however, the emission decay should be slowed down due to slow radiative relaxation from 4 I 13/2 to 4 I 15/2 on a millisecondmicrosecond time scale [18][19][20]. The fast energy transfer has already been related to Auger-type excitation of Er 3+ ions directly from the Si-NCs to 4 I 13/2 level of Er 3+ ions. In this case, excited ions should be inside the core of Si-NCs or at their surface due to the short range of Auger-type interactions. This mechanism can also be discussed since to obtain a high efficiency of Auger recombination within the Si-NCs, the energy levels of Si-NCs should be well separated from each other to minimize thermal relaxation which strongly reduces the Auger-type relaxation. It has been shown, however, theoretically that for Si-NCs, especially when surface/matrix interface is included into the calculations, the energy spectrum of Si-NCs is almost continuous above the main absorption edge [21,22]. Besides, it has been shown recently that in the spectral range of Er 3+ emission, another emission with nanosecond decay appears which, however, cannot be related to Er 3+ ions. This emission can be assigned more likely to defect states in the SRSO film. Thus, many open questions regarding the origin of the fast process still remain.

It is widely believed that the slow process is due to dipole-dipole energy transfer either from the exciton confined inside the Si-NCs or localized at their surface states. In this case, the transfer can occur efficiently (with a rate of 10 9 s −1 ) to the ions located even 6 to 7 nm from the Si-NCs, as has been shown by Choy et al. [23]. On the contrary, other authors have proposed that the optimal distance between Si-NCs and Er 3+ ions is on the order of 0.5 nm only [24,25]. With such a short interaction distance, the question regarding the nature of energy transfer and validity of dipole-dipole interaction only became important. Moreover, in case of slow energy transfer, the intermediate defect states in the SRSO matrix became important and can also participate in Er 3+ excitation allowing exciton migration before the exciton transfers its energy to Er 3+ ions. This should also increase the distance of Si-NC-Er 3+ interaction. In view of the above discussion, understanding of the origin of visible emission and temperature quenching of the emission of Er 3+ becomes important to understand the efficiency of coupling between Er 3+ and Si-NCs as well as the energy transfer between them.

There are several processes which might be responsible for temperature quenching of the photoluminescence (PL) in Si-NCs, such as (a) carriers' resonant/non-resonant tunneling out of Si-NCs to sites where the non-radiative recombination occurs [26], (b) thermal activation of carriers over the potential barrier Si/SiO 2 (3.4 eV) [27], and (c) simply non-radiative band-to-band transition. Other potential mechanisms, such as exciton dissociation (approximately 14 meV for bulk Si [28]) should rather be excluded from consideration in the case of Si-NCs since within the Si-NCs, there are no excitonic levels other than the ones related to Si-NCs itself, where the Columbic interaction has been included in self-consistent calculations. Thus, there are no additional levels to which the exciton could dissociate as in the case of bulk material. The only quenching energy which could be associated with exciton dissociation is one which moves one of the carriers to defect levels at the surface of Si-NCs over the potential barrier (process a or b). The only temperaturedependent emission-quenching mechanisms related to the excitonic nature of carriers confined within the Si-NCs can be due to different spin selection rules for different energy levels, which give the dark and bright states, which can be split in Si-NCs even with 20 meV [29].

In the case of erbium ions, PL quenching can be related to back-transfer mechanisms [30], which should be, however, very inefficient in Si-NCs because of the large difference in Er 3+ emission energy and the absorption edge of Si-NCs [31]. Another common mechanism responsible for the quenching of PL originating from Er 3+ is Auger recombination between excited Er 3+ and excess electrons bound to a surface/defect state at Si-NCs [32]. Finally, Er 3+ can transfer energy due to dipole-dipole interactions to other ions or to defect states which play the role of quenching centers. In order to be temperature-dependent, all these quenching processes should be phonon assisted.

In view of the above discussion, it can be seen that even if work on SRSO: Er 3+ -based LEDs is already advanced [7] from the fundamental point of view, there are many uncertainties and contradicting results in the literature. We believe that one of the main reasons is simplification of the interpretation of the obtained emission signal as related to Si-NCs only and the unappreciated role of the complex nature of the SRSO film where defects and both aSi-NCs and Si-NCs can be optically active simultaneously in the same spectral range. Moreover, in many cases, the 488-nm line is used for SRSO: Er 3+ excitation, where this wavelength overlaps with one of the optical transitions of Er 3+ ions and can bring about interpretation of obtained data.

In this work, we present new data regarding excitation, recombination, and thermal quenching of Er 3+ -related emission. As the absorption cross sections of Si-NCs and Er 3+ ions are different by orders of magnitude, the excitation of Er 3+ via Si-NCs at low excitation power should dominate over their direct excitation. Thus, as an additional aim of this work, we examine the optical properties of SRSO:Er 3+ at an excitation truly resonant with 4f-4f energy levels (980 nm), at indirect excitation (266 nm), and at 488-nm excitation wavelength, the non-resonant nature of which is questionable.

Methods

The Er-doped SRSO film was grown on a Si substrate by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) using SiH 4 and O 2 source gases diluted in Ar to form the SRSO matrix. Er (TMHD) 3 was employed as the rare-earth precursor to achieve high concentrations of Er doping. The film was annealed in a quartz tube furnace under flowing ultrahigh-purity N 2 for 1 h. The annealing temperature was 1,100°C. As we have shown in many previous papers, in our deposition system, this temperature is sufficient to obtain silicon nanocrystals of a few nanometers in size, both in the absence of erbium doping [33] and in the case of doping with erbium and different lanthanides [33,34]. The deposition system has been described in detail elsewhere [33]. The composition of the film (39 and 37 at.% of Si and 0.45 at.% of Er) was measured by Rutherford backscattering spectrometry. The film thickness estimated from ellipsometry experiments was 200 nm for both samples.

The room-temperature photoluminescence excitation (PLE) of the erbium ions in the near-infrared (NIR) was measured using an InGaAs pin photodiode. As an excitation source, a 450-W Xe arc lamp connected to a Triax 180 monochromator (Jobin-Yvon, Kyoto, Japan) was used. PL as a function of temperature was excited using a 488-nm Ar + CW laser (Melles Griot, Albuquerque, NW, USA), 266-nm (Elforlight, Daventry, UK) and 980-nm (Opolette ™ , Opotek Inc., Carlsbad, CA, USA) pulse lasers. An HR4000 spectrometer (Ocean Optics, Dunedin, FL, USA) and InGaAs CCD linear detector (Symphony W I line, Horiba Jobin-Yvon) were used as detection systems for measurements in the visible (VIS) and NIR spectral range, respectively. The PL decay was measured using pulsed laser coupled to a gated detection system (QuantaMaster from Photon Technology International, London, Canada). Figure 1a shows the PL spectra of SRSO films doped with Er 3+ ions measured at 500 and 10 K for samples with two Si atomic concentrations: 37 and 39 at.%. Two main emission bands at 1.6 and 0.81 eV have been observed. The first band at 0.81 eV is assigned to a radiative intra-4f shell transition of Er 3+ ions ( 4 I 13/2 → 4 I 15/2 ). The shape of this band at a high temperature can be modeled with a Boltzmann distribution for thermal populations of the crystal-field split manifold of 4 I 13/2 and 4 I 15/2 sublevels that have a total of 56 possible transitions between them, giving significant contribution to the observed broadening of this band.

Results and discussion

The second band at 1.6 eV can be assigned to the recombination of excitons localized in the SRSO matrix. Moreover, from Figure 1a, it can be seen that all VIS emission bands have a complex structure. This is due to interference effects caused by the refractive index contrast between SRSO and the Si substrate [35]. These interferences will modify the shape of the emission spectra in the entire VIS spectral range. However, Er 3+ emission is not affected by this effect.

Additionally, Figure 1a shows the PLE spectra measured for Er 3+ at room temperature at 0.81 eV in a broad UV-VIS excitation band energy range. The obtained PLE spectra are also very similar to those obtained by us for undoped SRSO samples [36,37]. The appearance of strong Er 3+ emission at excitation wavelengths far from resonance with erbium energy levels clearly indicates that we are dealing here with an efficient excitation transfer from the levels responsible for VIS emission (i.e., aSi-NCs, Si-NCs, or defects) to erbium ions. The main argument behind the conclusion that defect states can be excluded in this case is the Si-concentration-dependent position of the excitation spectra for Er 3+ ions and VIS emission bands. It can be seen that when the Si content increases, the edge of excitation as well as emission bands shifts towards lower energies due to reduction of quantum confinement. This suggests that the observed VIS emission can be related either to aSi-NCs or to Si-NCs. Moreover, the position of these excitation bands at 4.3 and 3.4 eV for 37 and 39 at.% of Si, respectively, seems to be different than energies typically obtained for excitation bands of defects in SiO 2 films: 'non-bridging oxygen hole center' at 4.8 and 5.8 eV [38], E' center at 5.4 to 6.2 eV [39], or 'oxygen-deficient center' (ODC) at 7.6, 6.9, and 5.0 eV [40].

Another important conclusion from Figure 1a is that the emission band in the VIS spectral range cannot be assigned to Si-NCs or aSi-NCs only, but some contribution from defect states can also be clearly observed, especially for the sample with 39 at.% where weak emission bands at around 450 nm can be observed. These defect states are most probably due to ODC in the SiO 2 matrix [41] or self-trapped excitons (STE) [42]. It has been shown that emission from ODC at this energy is characterized by a long emission decay time of 10 ms [40]. On the other hand, the emission decay time of STE should rather be in the nanosecond range. However, the nature of STE in SiO 2 is not clear at the moment. Nevertheless, we believe that emission at 1.6 eV originates mainly from aSi-NCs where the recombination is due to transitions between the tails of local density of states (LDOS) related to aSi-NCs rather than to the band-to-band excitonic transitions like in Si-NCs. One of the arguments strengthening our hypothesis can be seen in Figure 1c,d where the VIS emission peak position has been monitored with temperature ranging from 10 to 500 K for two excitation wavelengths. The PL peak position shows abnormal blueshift with increasing temperature. Usually, the PL peak position for unalloyed semiconductors shows a redshift with increasing temperature in accordance with Varshni's formula [43] shown also in Figure 1b with parameters typical for bulk Si. The temperature dependence of the PL peak position shown in Figure 1d is rather similar to the S-shaped phenomenon observed due to localized states caused by potential fluctuations in semiconducting alloys [44]. This should be a similar case for amorphous clusters. This is mainly because the tail states (N tail ) of aSi-NCs can be approximated as an exponential distribution [45],
N tail E ð Þ ¼ N TC ⋅ exp E À E m kT t :ð1Þ
Based on Equation 1, the carrier density trapped at localized tail states (n tail ) can be estimated using the Fermi-Dirac statistics,
n tail E; T ð Þ¼ Z E m E F0 N tail E ð Þ⋅ f E ð ÞdEð2Þ
where f(E) is the Fermi probability function defined as
f(E) = [1 + exp(E − E F /kT)] −1 ,
where k is Boltzmann's constant and T is the ambient temperature. Thus, at a low temperature, carriers relax to the lowest levels within the tails of LDOS. However, when the temperature increases, carriers move to higher lying levels and recombine at higher energies. Moreover, due to the increased role of non-radiative channels at a high temperature, the emission decay time is reduced, and thus, carriers can recombine from higher levels, also moving the emission band towards higher energies. Thus, the observed emission band at 1.6 eV can be related mainly to aSi-NCs. However, we cannot exclude additional contributions to the observed emission from Si-NCs. From Figure 1, we can clearly see the redshift of the total VIS emission with increasing Si content. Based on the above results, the observed shift can be explained as due to changes in aSi-NC sizes (redshift due to quantum confinement effect), changes in number of defect states making contributions to tails of LDOS (blue-or redshift), relative contribution of emission bands from matrix-related defect states, or Si-NC-and aSi-NCrelated emission. Moreover, increasing strain at the Si-NCs/SiO 2 interface with Si atomic percent should also be included as it has been shown by us recently elsewhere [46]. This can introduce defect states and can also influence the position of the energy levels related to Si-NCs inducing both red-and blueshift.

To analyze in detail the origin of the observed VIS emission bands, time-resolved PL spectra (TRPL) have been measured for two samples at 266-nm excitation wavelength. Obtained results are shown in Figure 2. Figure 2a,d shows emission spectra obtained just after the excitation with a laser pulse of less than 2 ns wherein the signal was collected during 1,000 μs. This condition should best reflect the emission signal obtained at the CW excitation shown in Figure 1. As it has been discussed already, the observed emission is composed of at least three independent emission bands overlapping each other spectrally. When the delay between the pulse and detection is set to 100 μs, two extreme bands disappear (Figure 2b,e). This means that their kinetics is much different (faster) than the one related to the main emission band centered at around 600 or 650 nm for 37 and 39 at.% of Si, respectively. To analyze this aspect further, the same TRPL spectra have been collected in a 100-ns window and recorded just after the 2-ns pulse. From the obtained results shown in Figure 2c,f, it can be seen that only the band on the highenergy side of the main emission can be observed. In this case, the integration window is too small to see the slow, main emission band. This band is related to the levels which just started to be populated. Some indication of this band can be seen as a second emission component shown in Figure 2c. Moreover, the position of defect-related bands is the same for both samples and does not depend on Si content. This is opposite to the behavior of the main band which shifts with Si content towards lower energies. This type of fast short-wavelength emission has been observed already and is considered to be caused most probably by STE. For this band, we were also able to measure the emission decay time, which is equal to 20 ns for both samples. Due to system limitations and weak signal of the main emission band (aSi-NCs), we were only able to estimate from TR-PL the average decay time as 500 μs.

Based on the results obtained so far, we conclude that the observed wide emission band obtained usually at CW excitation is a superposition of three emission subbands coming from spatially resolved objects with very different kinetics: (1) a band at around 450 nm, with 20-ns decay, which is not changing its position with Si content and is related to optically active defect states and STE in the SRSO matrix; (2) a band at around 600 nm related to aSi-NCs with hundreds of microsecond emission decay and strong dependence on Si content following the predictions of the quantum confinement model; (3) and a third band at around 800 nm (1.54 eV) (Si-NCs, defects) with either very fast (<3 ns) or very slow (>100 μs) emission kinetics also depending on Si content. In this case, however, an increase in Si content influences only the relative intensities between this band and the aSi-NC emission bands. This band can be related to Si-NCs or defect-related states. The weak dependence of the position of this band on Si content can be due to the weak quantum confinement regime. Based on our previous XRD and Raman results for similar samples, we can assume that the size of Si-NCs is in the range of 4 to 6 nm.

In summary, two components often obtained in emission decay times when the signal is recorded at one energy can be due to different spatially resolved objects (aSi-NCs and Si-NCs or defects) rather than two relaxation mechanisms different in timescale related with one object only, i.e., Si-NCs or aSi-NCs. The second conclusion that can be given based on the obtained preliminary results is that in many cases, the shift of the emission band at CW excitation observed for samples either annealed at different temperatures or obtained at different excess Si contents can be due to different contributions of defect states into this band. This shift is often related to changes in Si-NC size only. However, at the same time, these two technological parameters change also the number of defects in the matrix, induce a phase transition of Si clusters from amorphous to crystalline, influence the lanthanide distribution [3], and modify the strain at the clusters' interface, increasing/reducing the tails of density of states [46].

To better understand the dynamics of the Er 3+ -related emission, the time evolution of the 1,535-nm band has been analyzed at different excitation wavelengths: 266 and 488 nm. Figure 3 shows the obtained results together with maximum entropy method (MEM) analysis expressed in the form of α(τ).

In the analysis of kinetic experiments involving the relaxation of complex materials, such as rare-earth-doped glasses, it is often very difficult to choose appropriate models to fit the data. In particular, it is difficult to distinguish between non-exponential models (such as the 'stretched exponential') and models that consist of a few discrete exponentials. Thus, many authors use stretched exponential functions to fit the Er 3+ -related emission decay which, in many cases, is not justifiable. To prove the wellgrounded use of two exponential functions to fit our data instead of one exponential or a stretched exponential function, we calculated the inverse Laplace transform of the decay curves obtained by us. This solution allows us to seek a representation for the relaxation process in a space of decay rates, thus obviating the necessity of forcing a particular functional form to fit the data. In this case, the PL decay can be written as
I PL t ð Þ ¼ Z 1 0 g k ð Þ exp Àkt ð Þdkð3Þ
where g(k) is a distribution of decay rate constants for the process I(t). Given an experimental I(t), we would like to obtain the appropriate distribution g(k) that obeys Equation 3, without any assumption about the analytical form of g(k). This essentially involves performing a numerical inverse Laplace transform of the measured decay I(t) which can be written as
g k ð Þ ¼ 1 2πi Z Br exp Àkt ð ÞI t ð Þdtð4Þ
where the integration is carried out over the appropriate Bromwich contour. The calculation of an inverse Laplace transform on a noisy data function is known from information theory to be an ill-conditioned problem, and a large number of distributions can fit the data equally well. Nevertheless, it is possible to find the distribution g(k)

using the maximum entropy method. The MEM is based on maximizing a function called the Skilling-Jaynes entropy function
S ¼ Z 1 0 α τ ð Þ À m τ ð Þ log α τ ð Þ m τ ð Þ dτð5Þ
where α(τ) is the recovered distribution and m(τ) is the assumed starting distribution. In this equation, τ = 1/k, and the relation between g(k) and α(τ) is α(τ) = τ −2 g(1/τ). MEM allows finding α(τ) without any previous knowledge that we may have about the rate distribution. This method has been successfully applied in many situations where the inverse problem is highly degenerate, owing to the presence of noise in the data or the large parameter space one is working with. Thus, based on the above approach, we fit our data with two exponential functions. It should be mentioned that an important aspect of MEM is that even purely exponential decay processes have decay time distributions with finite width (unless the data is completely noiseless). Therefore, the broad distributions obtained by MEM, i.e., in the case of 488-nm excitation for 37 at.% of Si sample, do not necessarily imply non-exponential dynamics. A test to verify this is to fit the data with exponential decays taking the peaks of the distributions as the decay times. In the investigated case, the PL decay can be fitted very well with a two-exponential decay (χ 2 ≈ 1.0), yielding decay times of 4,860 and 885 μs and 2,830 and 360 μs for the samples with 37 and 39 at.% of Si, respectively. The obtained decay times are almost the same as the distribution peaks shown in Figure 3. This result allows us to conclude that the PL decay for both samples can be described by two exponential functions. It should be emphasized that this conclusion could not be drawn without MEM analysis since the PL decays can be fit well also with other models, e.g., the stretched exponential function of the form I(t)~t β−1 •exp(−(t/τ) β ). However, in the case of the stretched exponential function, the distribution α(τ) should exhibit the power-law asymptotic behavior of the form α(τ)~t β−1 , for t → 0, which is not the case.

Thus, at 266-nm excitation for both samples, we obtained emission decay times characterized by two components: a fast one (<1 ms) and a slow one (approximately 3 ms). Since the radiative transitions in Er 3+ are only weakly allowed, the cross sections for optical excitation and stimulated emission are quite small, typically in the order of 10 −21 cm 2 . Because of that, the radiative lifetime of the 4 I 13/2 → 4 I 15/2 transition in Er 3+ ions excited directly in SRSO should lie between 14 ms for pure silica [47] and 1 ms for silicon [48].

The longer time obtained by us is typical for times obtained by other authors (i.e., SiO, 2.5 to 3.5 ms [49] and SRSO, 2 to 11 ms [11,[50][51][52]). To explain the second component of our samples, we have three options: (a) Er 3+ ions are excited via aSi/Si-NCs, and there is only one optically active Er 3+ site excited by two temporally different mechanisms; (b) Er 3+ ions are excited via aSi/ Si-NCs, and there are two different Er 3+ sites, i.e., the isolated ion and clusters of ions; and (c) optically active Er 3+ ions are excited via Si-NCs and aSi-NCs or defect states separately with a different kinetics [53].

Nevertheless, even if the above models could explain two different times recorded for Er 3+ emission, the short time observed for Er 3+ seems to be much shorter than expected. This could be explained only by the assumption that the short emission decay can be related to Er 3+ ions which interact with each other, and due to ion-ion interaction, their emission time can be significantly reduced. Efficient clustering of lanthanides and especially Er 3+ ions has already been shown by us and other authors [3,25]. Thus, we propose that the slow component is due to emission from isolated ions, while the fast component is related with the ions in a cluster form.

Moreover, from Figure 3, it can be seen that with increase of Si content, the Er 3+ -related emission decay is reduced. We believe that this is due to changes in the refractive index of our matrix for both samples and its contribution to the expression defining the radiative emission time for lanthanides [54]:
A ED RJ 0 J ¼ 64π 4 e 2 3h λ 3 2J 0 þ 1 ð Þ n n 2 þ 2 ð Þ 2 9 X λ¼2;4;6 Ω λ Ψ J U λ Ψ 0J0 2ð6Þ1 τ R ¼ X J A ED R J 0 J ð Þð7Þ
where n is the refractive index of the matrix, <ΨJ0| and |ΨJ> are the initial and final states of single parity, U (λ) is the irreducible tensor form of the dipole operator, λ is the emission wavelength, and Ω λ are the Judd-Ofelt parameters, describing the local environment of the ion. We have observed similar effects of the influence of n on the emission decay time recently for Tb 3+ ions introduced into a SRSO matrix where the Si concentration was changed from 35% to 40%, increasing the refractive index from 1.55 to 1.70. Additionally, this reduction in decay time can be also due to an increased number of non-radiative channels with increasing Si content making contributions to the final emission decay as τ PL −1 = τ R −1 + τ NR −1 . Similar results have been obtained when 488 nm was used as the excitation wavelength. Moreover, reduction in emission decay time has been observed when the excitation wavelength is changed. The emission decay time at 488 and 266 nm can be different when two different sites are excited at different wavelengths. To verify this, emission spectra of Er 3+ ions obtained at 10 K have been compared at different excitation wavelengths. In the limit of our system resolution, we did not find any difference in the emission peak position at different excitation wavelengths. Thus, we believe that the same sites emit at 1,535 nm at all excitation wavelengths.

Thermal quenching

To investigate the effect of emission quenching, we have performed PL measurements as a function of temperature for different excitation wavelengths. In order to interpret these results, we considered the temperature dependence of the PL intensity at low pump power according to the Arrhenius law with E Q as deactivation (ionization) energy.

Based on the FTIR and Raman spectroscopy done on our samples previously [46], we found several absorption bands related with phonons or SRSO matrix vibrations which can participate in thermal quenching. Typical Raman spectra obtained by us for these samples consist of two bands: a broad low-frequency band (LF) with maximum at around 485 cm −1 (59 meV) and a narrower, asymmetrically broadened high-frequency (HF) peak centered at 520 cm −1 (64 meV). The LF band may be attributed to aSi present in the matrix, whereas the HF originates from Si-NCs. Moreover, from the FTIR spectra, there are three main bands located at 1,000 to 1,300 cm −1 (123 to 161 meV) and 800 cm −1 (100 meV) related to the asymmetric stretching and bending Si-O-Si modes, respectively.

In general, the quenching of the luminescence with temperature can be explained by thermal emission of the carriers out of a confining potential with an activation energy correlated with the depth of the confining potential. Since the observed activation energy is much less than the band offsets between Si/SiO 2 (approximately 3.4 eV), the thermal quenching of the aSi/Si-NC-related emission is not due to the simple thermal activation of electrons and/or holes from the aSi/Si-NCs potential into the SiO 2 barriers. Instead, the dominant mechanism leading to the quenching of the VIS-related PL is due to the phonon-assisted tunneling [55] of confined carriers to states at the interface between aSi/Si-NCs and the matrix.

As it can be seen from Figure 4c,f, for the excitation wavelength of 980 nm, thermal quenching of Er 3+ -related emission for both samples can be well characterized with only one deactivation energy (E Er Q1 ) equal to approximately 20 meV. Since the f levels of Er 3+ ions weakly couple to any matrix states due to screening effects of electrons filling higher orbitals, we believe that the observed quenching energy can be related with two mechanisms: Boltzmann distribution of carriers among the Stark levels having different radiative and non-radiative decay probabilities with one multiplet, or phonon-assisted dipoledipole coupling between the 4 I 13/2 → 4 I 15/2 transition and energy levels related with aSi/Si-NCs or defect states. The matrix-related emission in this spectral range with nanosecond dynamics has been shown already by other authors [16,56], making this process highly probable. Moreover, we can see that the intensity of the Er 3+ -related emission at this excitation varies by factors of 4 and 6 for samples with 37 and 39 at.% of Si. This is quite a significant change for RE 3+ , suggesting that the main quenching is due to the coupling of Er 3+ ions with some defect states. We can also see that this quenching is almost twice as large for the sample with 39 at.% of Si, suggesting correlation of these quenching centers with Si content in the SRSO matrix.

Analyzing the data presented in Figure 4a,d, we can see that when the Er 3+ is excited with 266 nm, PL thermal quenching can be well fitted only when two quenching energies are used. For both samples, these energies are equal to E Er Q1~1 5 meV and E Er Q2~5 0 meV. For comparison, in Figure 4a,d, two fits have been shown with one and two quenching energies. It is clear that two energies are needed to obtain a statistically good fit. Once we look at thermal quenching recorded for the emission related to aSi/Si-NCs, we can see that the thermal quenching can also be fitted with two energies similar for both samples: E VIS Q1~1 0 and E VIS Q2~6 5 meV. The E VIS Q2 energy corresponds exactly to the energy of phonons related to oscillations of Si-Si bonds obtained in Raman experiments. In more detail, this value is closer to the amorphous phase of silicon rather than the crystalline phase. This could be related to the fact that amorphous nanoclusters are responsible for the observed emission in the VIS range as well as for the indirect excitation of Er 3+ ions. Thus, most probably at a temperature corresponding to 65 meV, one of the carriers is moved from the potential related with aSi-NCs to defects states at their surface, where it recombines non-radiatively or diffuses over longer distances inside the matrix. The second energy (E VIS Q1 ) is much less clear at the moment. Nevertheless, correlation between the second quenching energy (55 meV) observed for Er 3+ emission with the quenching energy obtained for aSi-NC emission (65 meV) suggests efficient coupling between these two objects and confirms that most of the quenching appears before the excitation energy is transferred from aSi-NCs to Er 3+ ions. Also, at this excitation, Er 3+ -related emission is quenched by factors of 6 and 11 for samples with 37 and 39 at.% of Si, respectively. Figure 4e shows results of thermal emission quenching at 488-nm excitation wavelength for a sample with 39 at.% of Si. It can be seen that the Er 3+ -related emission is also (See figure on previous page.) Figure 4 Emission thermal quenching. Obtained for Si-NCs and Er 3+ -related bands at different excitation wavelengths (266, 488, and 980 nm) as function of temperature for two samples with 37 (a, b, c) and 39.at % of Si (d, e, f). Photon flux used for the experiment was equal to: Φ 266 nm = 8 × 10 19 , Φ 488 nm = 56 × 10 19 , Φ 980 nm = 570 × 10 19 (photons/s × cm 2 ) for 266, 488, and 980 nm, respectively. These fluxes correspond to the lowest excitation power allowing performance of the experiment and are equal to excitation power of 0.6, 6, and 40 mW for 266, 488, and 980 nm, respectively. Abbreviations used are as follows: f Q , relative change in emission intensity at 10 and 500 K; E Q , quenching energy from Arrhenius fit. characterized by two quenching energies equal to about 20 and 60 meV. These values are almost the same as for 266-nm excitation and very similar to VIS emission where values of 15 and 70 meV have been obtained. This indicates that in this case also, we deal with indirect excitation of Er 3+ ions. Since 488 nm corresponds also to direct excitation of Er 3+ ions, most probably, we deal with both kinds of excitation simultaneously. We believe, however, that indirect excitation is in this case dominant. Nevertheless, the results obtained at this excitation wavelength for 37 at.% of Si are not so obvious. In this case, two statistically equal fits with one (20 meV) and two energies (20 and 6 meV) were possible to achieve. The higher energy is clear and has the same origin as in the previous cases. One explanation of this fact would be the excitation spectrum for this sample where its edge is much shifted to blue as compared to samples with 39 at.% of Si. Thus, in this case, we can indeed observe a major contribution from a direct excitation of Er 3+ ions rather than via intermediate states.

Conclusions

The existence of efficient excitation transfer from silicon nanoclusters to Er 3+ ions has been shown for SRSO thin films deposited by ECR-PECVD by means of PL, TRPL, PLE and temperature-dependent PL experiments. However, it has been shown that for our samples, this energy transfer is most efficient at high excitation energies. Much less efficient energy transfer has been observed at 488-nm excitation. In this case, depending on Si nanocluster size, we deal with dominant contribution to Er 3+ excitation from indirect excitation channel (big nanoclusters) or from direct excitation of Er 3+ ions (small nanoclusters).

Moreover, it has been shown that a wide emission band in the VIS spectral range is a superposition of three emission sub-bands coming from spatially resolved objects with very different kinetics: a band at around 450 nm, with 20-ns decay, which is not changing with Si content and is related with optically active defect states and STE in SRSO matrix; a band at approximately 600 nm related to aSi-NCs with hundred-microsecond emission decay and strong dependence on Si content following the predictions of quantum confinement model; and a third band at around 800 nm (1.54 eV) (Si-NCs, defects) with either very fast (<3 ns) or very slow (>100 μs) emission kinetics, also depending on Si content. Additionally, it has been shown that two Er 3+ sites are present in our samples: isolated ions and clustered ions with emission decay times of approximately 3 and <1 ms, respectively.

Figure 1
1Results of photoluminescence measurements. PL spectra of Si-NCs (VIS) doped with Er 3+ (NIR) measured at 10 and 300 K at 488-nm excitation together with normalized PLE spectra detected at 0.81 eV for two Si concentrations: (a) 37 at.% and (b) 39 at.% of Si. The normalization was done for both spectra separately. Emission peak positions as function of temperature for two excitation wavelengths, 266 (squares) and 488 nm (circles), for two different Si concentrations, (c) 37 at.% and (d) 39 at.%, together with theoretically predicted Varshni formula. For the Varshni formula, Si bandgap at 0 K has been set as 2.3 eV for better data presentation.

Figure 2
2Time-resolved PL spectra. SRSO:Er 3+ samples obtained at 266-nm excitation for (a, b, c) 37% and (d, e, f) 39% of Si. Δt, integrating time; Δt, delay time.

Figure 3
3Time evolution of the 1,535-nm band. (a) PL decay obtained for samples with 37 and 39 at.% of Si at 266 and (b) 488 nm. (c) MEM distribution of emission decay at 266-nm excitation for 37 and 39 at.% of Si and (d) MEM distribution of emission decay at 488-nm excitation for 37 and 39 at.% of Si.

Figure 4 (
4See legend on next page.)
http://www.nanoscalereslett.com/content/8/1/98
Podhorodecki et al. Nanoscale Research Letters 2013, 8:98
Competing interestsThe authors declare that they have no competing interests.Authors' contributions AP, GZ, LG, and JM carried out the spectroscopic measurements. JW and PM designed and deposited the investigated samples. All authors read and approved the final manuscript.Submit your manuscript to a journal and benefi t from:7 Convenient online submission 7 Rigorous peer review 7 Immediate publication on acceptance 7 Open access: articles freely available online 7 High visibility within the fi eld 7 Retaining the copyright to your article Submit your next manuscript at 7 springeropen.com
Direct evidence of the energy transfer from silicon nanocrystals to Nd ions. A Podhorodecki, J Misiewicz, F Gourbilleau, C Dufour, Electrochemical Solid State Lett. 13Podhorodecki A, Misiewicz J, Gourbilleau F, Dufour C: Direct evidence of the energy transfer from silicon nanocrystals to Nd ions. Electrochemical Solid State Lett 2010, 13:K26-K28.

Excitation of Nd 3+ and Tm 3+ by energy transfer from Si nanocrystals. K Watanabe, H Tamaoka, M Fujii, K Moriwaki, S Hayashi, Physica E. 13Watanabe K, Tamaoka H, Fujii M, Moriwaki K, Hayashi S: Excitation of Nd 3+ and Tm 3+ by energy transfer from Si nanocrystals. Physica E 2002, 13:1038-1042.

Green light emission from terbium doped silicon rich silicon oxide films obtained by plasma enhanced chemical vapor deposition. A Podhorodecki, G Zatryb, J Misiewicz, J Wojcik, Prj Wilson, P Mascher, Nanotechnology. 23475707Podhorodecki A, Zatryb G, Misiewicz J, Wojcik J, Wilson PRJ, Mascher P: Green light emission from terbium doped silicon rich silicon oxide films obtained by plasma enhanced chemical vapor deposition. Nanotechnology 2012, 23:475707.

Photoluminescence excitation spectroscopy of erbium-doped silicon-rich silicon oxide. J H Shin, S Y Seo, S Kim, S G Bishop, Appl Phys Lett. 76Shin JH, Seo SY, Kim S, Bishop SG: Photoluminescence excitation spectroscopy of erbium-doped silicon-rich silicon oxide. Appl Phys Lett 1999, 2000:76.

Long lifetime and efficient emission from Er 3+ ions coupled to Si nanoclusters in Si-rich SiO 2 layers. L Khomenkova, F Gourbilleau, J Cardin, O Jambois, B Garrido, R Rizk, J Lum. 129Khomenkova L, Gourbilleau F, Cardin J, Jambois O, Garrido B, Rizk R: Long lifetime and efficient emission from Er 3+ ions coupled to Si nanoclusters in Si-rich SiO 2 layers. J Lum 2009, 129:1519-1523.

Photoreflectance investigations of quantum well intermixing processes in compressively strained InGaAsP/InGaAsP QW laser structures emitting at 1.55 μm. A Podhorodecki, A Andrzejewski, R Kudrawiec, J Misiewicz, J Wojcik, B J Robinson, T Roschuk, D A Thompson, P Mascher, J App Phys. 100Podhorodecki A, Andrzejewski A, Kudrawiec R, Misiewicz J, Wojcik J, Robinson BJ, Roschuk T, Thompson DA, Mascher P: Photoreflectance investigations of quantum well intermixing processes in compressively strained InGaAsP/InGaAsP QW laser structures emitting at 1.55 μm. J App Phys 2006, 100:013111-1-013111-12.

Erbium emission in MOS light emitting devices: from energy transfer to direct impact excitation. J M Ramirez, F F Lupi, O Jambois, Y Berencen, D Navarro-Urrios, A Anopchenko, A Marconi, N Prtljaga, A Tengattini, L Pavesi, J P Colonna, J M Fedeli, B Garrido, Nanotechnology. 23125203Ramirez JM, Lupi FF, Jambois O, Berencen Y, Navarro-Urrios D, Anopchenko A, Marconi A, Prtljaga N, Tengattini A, Pavesi L, Colonna JP, Fedeli JM, Garrido B: Erbium emission in MOS light emitting devices: from energy transfer to direct impact excitation. Nanotechnology 2012, 23:125203.

Energy transfer in rare-earth-doped III-V semiconductors. K Takahei, A Taguchi, Mater Sci Forum. Takahei K, Taguchi A: Energy transfer in rare-earth-doped III-V semiconductors. Mater Sci Forum 1992, 83-87:641-652.

Role of the energy transfer in the optical properties of undoped and Er-doped interacting Si nanocrystals. F Priolo, G Franzò, D Pacifici, V Vinciguerra, F Iacona, A Irrera, J Appl Phys. 89264Priolo F, Franzò G, Pacifici D, Vinciguerra V, Iacona F, Irrera A: Role of the energy transfer in the optical properties of undoped and Er-doped interacting Si nanocrystals. J Appl Phys 2001, 89:264.

Sensitizing properties of amorphous Si clusters on the 1.54-μm luminescence of Er in Si-rich SiO2. G Franzo, S Boninelli, D Pacifici, F Priolo, F Iacona, C Bongiorno, Appl Phys Lett. 823871Franzo G, Boninelli S, Pacifici D, Priolo F, Iacona F, Bongiorno C: Sensitizing properties of amorphous Si clusters on the 1.54-μm luminescence of Er in Si-rich SiO2. Appl Phys Lett 2003, 82:3871.

Optimized conditions for an enhanced coupling rate between Er ions and Si nanoclusters for an improved 1.54-μm emission. F Gourbilleau, M Levalois, C Dufour, J Vicens, R Rizk, J Appl Phys. 953717Gourbilleau F, Levalois M, Dufour C, Vicens J, Rizk R: Optimized conditions for an enhanced coupling rate between Er ions and Si nanoclusters for an improved 1.54-μm emission. J Appl Phys 2004, 95:3717.

Sensitization of Er luminescence by Si nanoclusters. M Wojdak, M Klik, M Forcales, O B Gusev, T Gregorkiewicz, D Pacifici, G Franzò, F Priolo, F Iacona, Phys Rev B. 69233315Wojdak M, Klik M, Forcales M, Gusev OB, Gregorkiewicz T, Pacifici D, Franzò G, Priolo F, Iacona F: Sensitization of Er luminescence by Si nanoclusters. Phys Rev B 2004, 69:233315.

Excitable Er fraction and quenching phenomena in Er-doped SiO 2 layers containing Si nanoclusters. B Garrido, C Garcia, S Y Seo, P Pellegrino, D Navarro-Urrios, N Daldosso, L Pavesi, F Gourbilleau, R Rizk, Phys Rev B. 76245308Garrido B, Garcia C, Seo SY, Pellegrino P, Navarro-Urrios D, Daldosso N, Pavesi L, Gourbilleau F, Rizk R: Excitable Er fraction and quenching phenomena in Er-doped SiO 2 layers containing Si nanoclusters. Phys Rev B 2007, 76:245308.

Exciton-erbium interactions in Si nanocrystal-doped SiO 2. P G Kik, A Polman, J Appl Phys. 88Kik PG, Polman A: Exciton-erbium interactions in Si nanocrystal-doped SiO 2 . J Appl Phys 1992, 2000:88.

Gain limiting processes in Er-doped Si nanocrystal waveguides in SiO 2. P G Kik, A Polman, J Appl Phys. 91534Kik PG, Polman A: Gain limiting processes in Er-doped Si nanocrystal waveguides in SiO 2 . J Appl Phys 2002, 91:534.

Energy transfer between amorphous Si nanoclusters and Er 3+ ions in SiO 2 matrix. D Navarro-Urrios, A Pitanti, N Daldosso, F Gourbilleau, R Rizk, B Garrido, L Pavesi, Phys Rev B. 79Navarro-Urrios D, Pitanti A, Daldosso N, Gourbilleau F, Rizk R, Garrido B, Pavesi L: Energy transfer between amorphous Si nanoclusters and Er 3+ ions in SiO 2 matrix. Phys Rev B 2009, 79:193312.

Maximum fraction of Er 3+ ions optically pumped through Si nanoclusters. C Garcia, P Pellegrino, Y Lebour, B Garrido, F Gourbilleau, R Rizk, J Lumin. 121Garcia C, Pellegrino P, Lebour Y, Garrido B, Gourbilleau F, Rizk R: Maximum fraction of Er 3+ ions optically pumped through Si nanoclusters. J Lumin 2006, 121:204-208.

Coexistence of two different energy transfer processes in SiO 2 films containing Si nanocrystals and Er. F Fujii, K Imakita, K Watanabe, S Hayashi, J Appl Phys. 95272Fujii F, Imakita K, Watanabe K, Hayashi S: Coexistence of two different energy transfer processes in SiO 2 films containing Si nanocrystals and Er. J Appl Phys 2004, 95:272.

Observation of temperatureindependent internal Er 3+ relaxation efficiency in Si-rich SiO 2 films. O Savchyn, R M Todi, K R Coffey, P G Kik, Appl Phys Lett. 4241115Savchyn O, Todi RM, Coffey KR, Kik PG: Observation of temperature- independent internal Er 3+ relaxation efficiency in Si-rich SiO 2 films. Appl Phys Lett 2009, 4:241115.

Nanosecond dynamics of the near-infrared photoluminescence of Er-Doped SiO 2 sensitized with Si nanocrystals. I Izeddin, A S Moskalenko, I N Yassievich, M Fujii, T Gregorkiewicz, Phys Rev Lett. 97207401Izeddin I, Moskalenko AS, Yassievich IN, Fujii M, Gregorkiewicz T: Nanosecond dynamics of the near-infrared photoluminescence of Er- Doped SiO 2 sensitized with Si nanocrystals. Phys Rev Lett 2006, 97:207401.

Influence of SiO 2 matrix on electronic and optical properties of Si nanocrystals. K Seino, F Bechstedt, P Kroll, Nanotechnology. 20135702Seino K, Bechstedt F, Kroll P: Influence of SiO 2 matrix on electronic and optical properties of Si nanocrystals. Nanotechnology 2009, 20:135702.

Silicon nanocrystallites in a SiO 2 matrix: role of disorder and size. R Guerra, I Marri, R Magri, L Martin-Samos, O Pulci, E Degoli, S Ossicini, Phys Rev B. 79155320Guerra R, Marri I, Magri R, Martin-Samos L, Pulci O, Degoli E, Ossicini S: Silicon nanocrystallites in a SiO 2 matrix: role of disorder and size. Phys Rev B 2009, 79:155320.

Geometrical effects in the energy transfer mechanism for silicon nanocrystals and Er 3+. K Choy, F Lenz, X X Liang, F Marsiglio, A Meldrum, Appl Phys Lett. 93261109Choy K, Lenz F, Liang XX, Marsiglio F, Meldrum A: Geometrical effects in the energy transfer mechanism for silicon nanocrystals and Er 3+ . Appl Phys Lett 2008, 93:261109.

Effects of Si nanocluster size and carrier-Er interaction distance on the efficiency of energy transfer. F Gourbilleau, C Dufour, R Madelon, R Rizk, J Lumin. 126Gourbilleau F, Dufour C, Madelon R, Rizk R: Effects of Si nanocluster size and carrier-Er interaction distance on the efficiency of energy transfer. J Lumin 2007, 126:581-589.

Site of Er ions in silica layers codoped with Si nanoclusters and Er. P Pellegrino, B Garrido, J Arbiol, C Garcia, Y Lebour, J R Morante, Appl Phys Lett. 88121915Pellegrino P, Garrido B, Arbiol J, Garcia C, Lebour Y, Morante JR: Site of Er ions in silica layers codoped with Si nanoclusters and Er. Appl Phys Lett 2006, 88:121915.

Mechanisms of visible-light emission from electro-oxidized porous silicon. J C Vial, A Bsiesy, F Gaspard, R Herino, M Ligeon, F Muller, R Romestain, Phys Rev B. 4514171Vial JC, Bsiesy A, Gaspard F, Herino R, Ligeon M, Muller F, Romestain R: Mechanisms of visible-light emission from electro-oxidized porous silicon. Phys Rev B 1992, 45:14171.

Interpretation of the temperature dependence of the luminescence intensity, lifetime, and decay profiles in porous Si. T Suemoto, K Tanaka, A Nakajima, Phys Rev B. 4911005Suemoto T, Tanaka K, Nakajima A: Interpretation of the temperature dependence of the luminescence intensity, lifetime, and decay profiles in porous Si. Phys Rev B 1994, 49:11005.

Valley-orbit splitting of free excitons? The absorption edge of Si. K L Shaklee, R E Nahory, Phys Rev Lett. 24942Shaklee KL, Nahory RE: Valley-orbit splitting of free excitons? The absorption edge of Si. Phys Rev Lett 1970, 24:942.

Size-dependent electron-hole exchange interaction in Si nanocrystals. M L Brongersma, P G Kik, A Polman, K S Min, H A Atwater, Appl Phys Lett. 76351Brongersma ML, Kik PG, Polman A, Min KS, Atwater HA: Size-dependent electron-hole exchange interaction in Si nanocrystals. Appl Phys Lett 2000, 76:351.

Excitation and nonradiative deexcitation processes of Er 3+ in crystalline Si. F Priolo, G Franzo, S Coffa, A Carnera, Phys Rev B. 574443Priolo F, Franzo G, Coffa S, Carnera A: Excitation and nonradiative deexcitation processes of Er 3+ in crystalline Si. Phys Rev B 1998, 57:4443.

Optical band gap of Si nanoclusters. C Delerue, G Allan, M Lannoo, J Lum. 8065Delerue C, Allan G, Lannoo M: Optical band gap of Si nanoclusters. J Lum 1999, 80:65.

Interaction between Er ions and shallow impurities in Si nanocrystals within SiO 2. K Imakita, M Fujii, Y Yamaguchi, S Hayashi, Phys Rev B. 71115440Imakita K, Fujii M, Yamaguchi Y, Hayashi S: Interaction between Er ions and shallow impurities in Si nanocrystals within SiO 2 . Phys Rev B 2005, 71:115440.

X-ray-diffraction study of crystalline Si nanocluster formation in annealed silicon-rich silicon oxides. D Comedi, Ohy Zalloum, E A Irving, J Wojcik, T Roschuk, M J Flynn, P Mascher, J Appl Phys. 9923518Comedi D, Zalloum OHY, Irving EA, Wojcik J, Roschuk T, Flynn MJ, Mascher P: X-ray-diffraction study of crystalline Si nanocluster formation in annealed silicon-rich silicon oxides. J Appl Phys 2006, 99:023518.

On the effects of double-step anneal treatments on light emission from Er-doped Si-rich silicon oxide. C L Heng, Ohy Zalloum, J Wojcik, T Roschuk, P Mascher, J Appl Phys. 10324309Heng CL, Zalloum OHY, Wojcik J, Roschuk T, Mascher P: On the effects of double-step anneal treatments on light emission from Er-doped Si-rich silicon oxide. J Appl Phys 2008, 103:024309.

Influence of the annealing temperature and silicon concentration on the absorption and emission properties of Si nanocrystals. A Podhorodecki, G Zatryb, J Misiewicz, J Wojcik, P Mascher, J Appl Phys. 10243104Podhorodecki A, Zatryb G, Misiewicz J, Wojcik J, Mascher P: Influence of the annealing temperature and silicon concentration on the absorption and emission properties of Si nanocrystals. J Appl Phys 2007, 102:043104.

Absorption mechanisms of silicon nanocrystals obtained at different hydrogen partial pressure in co-sputtered (SRSO) film. Electrochemical Solid State Lett. A Podhorodecki, J Misiewicz, F Gourbilleau, R Rizk, 11Podhorodecki A, Misiewicz J, Gourbilleau F, Rizk R: Absorption mechanisms of silicon nanocrystals obtained at different hydrogen partial pressure in co-sputtered (SRSO) film. Electrochemical Solid State Lett. 2008, 11:K31-K33.

Effects of non-stoichiometry of O/Si ratio on the structural and optical properties of silicon quantum dots in a silicon dioxide matrix. X J Hao, A Podhorodecki, Y S Shen, G Zatryb, J Misiewicz, M A Green, Nanotechnology. 20485703Hao XJ, Podhorodecki A, Shen YS, Zatryb G, Misiewicz J, Green MA: Effects of non-stoichiometry of O/Si ratio on the structural and optical properties of silicon quantum dots in a silicon dioxide matrix. Nanotechnology 2009, 20:485703.

Defects in SiO 2 and Related Dielectrics: Science and Technology. G Pacchioni, L Skuja, D L Griscom, Springer73New YorkPacchioni G, Skuja L, Griscom DL: Defects in SiO 2 and Related Dielectrics: Science and Technology. New York: Springer; 2000:73.

Analysis of OSEE spectra of irradiated dielectrics. A F Zatsepin, D Y Biryukov, V S Kortov, Latv J Phys Tech Sci. 683Zatsepin AF, Biryukov DY, Kortov VS: Analysis of OSEE spectra of irradiated dielectrics. Latv J Phys Tech Sci 2000, 6:83.

Quantitative analysis of the concentration of interstitial O 2 molecules in SiO 2 glass using luminescence and Raman spectroscopy. L Skuja, B Güttler, D Schiel, A R Silin, J Appl Phys. 836106Skuja L, Güttler B, Schiel D, Silin AR: Quantitative analysis of the concentration of interstitial O 2 molecules in SiO 2 glass using luminescence and Raman spectroscopy. J Appl Phys 1998, 83:6106.

Investigation of emitting centers in SiO2 codoped with silicon nanoclusters and Er3+ ions by cathodoluminescence technique. S Cueff, C Labbé, B Dierre, F Fabbri, T Sekiguchi, X Portier, R Rizk, J Appl Phys. 108113504Cueff S, Labbé C, Dierre B, Fabbri F, Sekiguchi T, Portier X, Rizk R: Investigation of emitting centers in SiO2 codoped with silicon nanoclusters and Er3+ ions by cathodoluminescence technique. J Appl Phys 2010, 108:113504.

Kathodolumineszenz amorpher und kristalliner Modifikationen von SiO 2 und GeO 2 . PhD dissertation: Rostock University. T Barfels, Barfels T: Kathodolumineszenz amorpher und kristalliner Modifikationen von SiO 2 und GeO 2 . PhD dissertation: Rostock University; 2001.

Temperature dependence of the energy gap in semiconductors. V P Varshni, Physica. 34149Varshni VP: Temperature dependence of the energy gap in semiconductors. Physica 1967, 34:149.

S-shaped temperature-dependent emission shift and carrier dynamics in InGaN/GaN multiple quantum wells. Y Cho, G H Gainer, H J Fischer, J J Song, S Keller, U K Mishra, S P Denbaars, Appl Phys Lett. 731370Cho Y, Gainer GH, Fischer HJ, Song JJ, Keller S, Mishra UK, DenBaars SP: S-shaped temperature-dependent emission shift and carrier dynamics in InGaN/GaN multiple quantum wells. Appl Phys Lett 1998, 73:1370.

R A Street, Hydrogenated Amorphous Silicon. CambridgeCambridge University PressStreet RA: Hydrogenated Amorphous Silicon. Cambridge: Cambridge University Press; 2005. Chap. 7.

Correlation between stress and carriers nonradiative recombination for silicon nanocrystals in an oxide matrix. G Zatryb, A Podhorodecki, X J Hao, J Misiewicz, Y S Shen, M A Green, Nanotechnology. 22335703Zatryb G, Podhorodecki A, Hao XJ, Misiewicz J, Shen YS, Green MA: Correlation between stress and carriers nonradiative recombination for silicon nanocrystals in an oxide matrix. Nanotechnology 2011, 22:335703.

Erbium implanted thin film photonic materials. A Polman, J Appl Phys. 821Polman A: Erbium implanted thin film photonic materials. J Appl Phys 1997, 82:1.

Optically active erbium centers in silicon. H Przybyliska, W Jantsch, Y Suprun-Belevitch, M Stephikova, L Palmetshofer, G Hendorfer, A Kozanecki, R J Wilson, B J Sealy, Phys Rev B. 542532Przybyliska H, Jantsch W, Suprun-Belevitch Y, Stephikova M, Palmetshofer L, Hendorfer G, Kozanecki A, Wilson RJ, Sealy BJ: Optically active erbium centers in silicon. Phys Rev B 1996, 54:2532.

Fabrication and photoluminescence properties of erbium doped size-controlled silicon nanocrystals. J Heitmann, M Schmidt, M Zacharias, V Y Timoshenko, M G Lisachenko, P K Kashkarov, Materials Science and Engineering B. 105Heitmann J, Schmidt M, Zacharias M, Timoshenko VY, Lisachenko MG, Kashkarov PK: Fabrication and photoluminescence properties of erbium doped size-controlled silicon nanocrystals. Materials Science and Engineering B 2003, 105:214-220.

Time dependence and excitation spectra of the photoluminescence emission at 1.54lm in Si-nanocluster and Er codoped silica. M Falconieri, E Borsella, F Enrichi, G Franzo, F Priolo, F Iacona, F Gourbilleau, R Rizk, Opt Mater. 27Falconieri M, Borsella E, Enrichi F, Franzo G, Priolo F, Iacona F, Gourbilleau F, Rizk R: Time dependence and excitation spectra of the photoluminescence emission at 1.54lm in Si-nanocluster and Er co- doped silica. Opt Mater 2005, 27:884-889.

Probe of the Si nanoclusters to Er 3+ energy transfer dynamics by double-pulse excitation. M Falconieri, E Borsella, De Dominicis, L Enrichi, F Franzò, G Priolo, F Iacona, F Gourbilleau, F Rizk, R , Appl Phys Lett. 8761109Falconieri M, Borsella E, De Dominicis L, Enrichi F, Franzò G, Priolo F, Iacona F, Gourbilleau F, Rizk R: Probe of the Si nanoclusters to Er 3+ energy transfer dynamics by double-pulse excitation. Appl Phys Lett 2005, 87:061109.

Resonant excitation of Er 3+ by the energy transfer from Si nanocrystals. K Watanabe, M Fuji, S Hayashi, J Appl Phys. 904761Watanabe K, Fuji M, Hayashi S: Resonant excitation of Er 3+ by the energy transfer from Si nanocrystals. J Appl Phys 2001, 90:4761.

Defect-mediated and resonant optical excitation of Er 3+ ions in silicon-rich silicon oxide. D Kuritsyn, A Kozanecki, H Przybylinska, W Jantsch, Appl Phys Lett. 834160Kuritsyn D, Kozanecki A, Przybylinska H, Jantsch W: Defect-mediated and resonant optical excitation of Er 3+ ions in silicon-rich silicon oxide. Appl Phys Lett 2003, 83:4160.

Handbook of the Physics and Chemistry of Rare Earths. K A Gschneidner, Elsevier25PhiladelphiaGschneidner KA: Handbook of the Physics and Chemistry of Rare Earths. Philadelphia: Elsevier; 1998:25.

Temperature dependent emission quenching in silicon-rich oxide films. A Podhorodecki, G Zatryb, J Misiewicz, F Gourbilleau, C Dufour, J Nanoscience and Nanotechnology. 101Podhorodecki A, Zatryb G, Misiewicz J, Gourbilleau F, Dufour C: Temperature dependent emission quenching in silicon-rich oxide films. J Nanoscience and Nanotechnology 2010, 10:1.

Dynamics and microscopic origin of fast 1.5 μm emission in Er-doped SiO2 sensitized with Si nanocrystals. S Saeed, D Timmerman, T Gregorkiewicz, 10.1186/1556-276X-8-98Phys Rev B. 83155323Saeed S, Timmerman D, Gregorkiewicz T: Dynamics and microscopic origin of fast 1.5 μm emission in Er-doped SiO2 sensitized with Si nanocrystals. Phys Rev B 2011, 83:155323. doi:10.1186/1556-276X-8-98

On the origin of emission and thermal quenching of SRSO:Er 3+ films grown by ECR-PECVD. Podhorodecki, Nanoscale Research Letters. 898Cite this article asCite this article as: Podhorodecki et al.: On the origin of emission and thermal quenching of SRSO:Er 3+ films grown by ECR-PECVD. Nanoscale Research Letters 2013 8:98.


A model for mentoring newly-appointed nurse educators in nursing education institutions in South Africa
24 Apr. 2014

Eunice Seekoe email@example.com
School of Health Sciences
University of Fort Hare
South Africa

7th Floor Gasson Centre
PO Box 10545200East London Campus, East LondonSouth Africa

A model for mentoring newly-appointed nurse educators in nursing education institutions in South Africa
24 Apr. 2014303BEF8AC675F3219D77863205F64C5110.4102/curationis.v37i1.132Received: 10 Sep. 2012 Accepted: 23 Nov. 2013
Background: South Africa transformed higher education through the enactment of the Higher Education Act (No. 101 of 1997).The researcher identified the need to develop a model for the mentoring of newly-appointed nurse educators in nursing education institutions in South Africa.Objectives: To develop and describe the model for mentoring newly-appointed nurse educators in nursing education institutions in South Africa.Method:A qualitative and theory-generating design was used (following empirical findings regarding needs analysis) in order to develop the model.The conceptualisation of the framework focused on the context, content, process and the theoretical domains that influenced the model.Ideas from different theories were borrowed from and integrated with the literature and deductive and inductive strategies were applied.Results:The structure of the model is multidimensional and complex in nature (macro, meso and micro) based on the philosophy of reflective practice, competency-based practice and critical learning theories.The assumptions are in relation to stakeholders, context, mentoring, outcome, process and dynamic.The stakeholders are the mentor and mentee within an interactive participatory relationship.The mentoring takes place within the process with a sequence of activities such as relationship building, development, engagement, reflective process and assessment.Capacity building and empowerment are outcomes of mentoring driven by motivation.Conclusion:The implication for nurse managers is that the model can be used to develop mentoring programmes for newly-appointed nurse educators.

Introduction

The purpose of the article was to describe the model for mentoring of newly-appointed nurse educators in nursing education institutions in South Africa.In South Africa, nursing education is regulated by the South African Nursing Council (SANC), in accordance with the Nursing Act (No. 33 of 2005) (South Africa 2005) relating to nursing education institutions.The SANC acts as an accreditation and education and training quality assurance body (ETQA) for nursing education (South African Nursing Council 2005:5).Nursing education institutions are approved or accredited by the SANC as nursing colleges (public or private) or as departments or schools of nursing within higher education institutions.Higher education institutions broadened and changed their vision, mission and mandates as a result of changes in economic climate, needs of communities and the knowledge explosion in accordance with the government transformation framework (Büchner & Hay 1998:20;Council on Higher Education 2004:1;South Africa 2000:2).

Change in nursing education has, in the same way, been brought about by redress of the past inequalities of the education system in South Africa.This change has led to an increase in student numbers with the consequences of multiculturalism, multilingualism and multiracialism, which were not prevalent in the previous higher education system in South Africa (South Africa 2000:2).This growth is not only seen in the student body but also in the academic staff's workload and the need for institutional development, creativity and innovation in teaching and learning (South Africa 2000:2).The increase in student numbers has impacted on the number of newly-qualified nurse educators.Nursing education institutions were challenged to recruit more academic staff members and there was consequently a greater need for the mentoring of newly-appointed nurse educators (NANEs) (South Africa 2000:2).Historically-disadvantaged nurse educators do not have easy access to higher education institutions because of a lack of required competencies.Those who have required qualifications such as Masters degrees find it difficult to climb the ladder of success because of a lack of support and mentoring by more experienced nurse educators.This leads to a shortage of qualified staff of this calibre in higher education (Greyling 2003:8).

In South Africa, nursing colleges are classified as higher education institutions and are expected to comply with the quality requirements of the Higher Education Act No. 101 of 1997 (South Africa Page 1 of 8 Scan this QR code with your smart phone or mobile device to read online.

Read online:

1997) and the Nursing Act No. 33 of 2005(South Africa 2005).However, although the management of nursing colleges falls under the control of the Department of Health in nine different provinces, the academic quality control is regarded as being the responsibility of the universities.The nurse educators are appointed by the Department of Health and their conditions of service are controlled by the human resources department of their respective provinces.Nurse educators at universities are appointed by their respective universities and their conditions of service are controlled by the human resources departments of their universities.Nurse educators in both environments are oriented in and accustomed to the institutions through induction programmes offered by their institutions.Neither environment has sufficient mentoring programmes (Greyling 2003:8).Nurse educators appointed at universities have an added responsibility of being moderators for the theoretical and clinical teaching programmes offered by the nursing colleges in order to ensure quality teaching.The educators at universities are also expected to have more expertise than those at nursing colleges (Booyens 1998:381;Muller 2002:261).Nursing colleges are still affected by the same problems that characterise higher education in South Africa, such as the need to ensure quality and the increase in student numbers, which leads to an increase in the workload of nurse educators.It is, therefore, important for all efforts directed at improving the conditions and quality of education in higher education to apply to all colleges of nursing as well.Nurse educators at colleges and universities need to be mentored by their senior nurse educators in order to ensure adaptation to the institutional culture as well as academic and career success (South Africa 2000).

There is a lack of support for the NANEs in higher education institutions, which exacerbates the high staff turnover.Thirty percent of these lecturers leave the institution within the first five years, which is tremendously costly, in terms of both human and economic resources (O'Brien 2003:10).To be successful in their vision and/or mission of teaching students the nurse educators must focus on improving the quality of their schools and/or departments, which can be accomplished through senior nurse educators mentoring their newly-appointed and junior colleagues (English, Bonaguro & Madison 2005:296).This can help reduce the rate of attrition and improve the nurse educators' skills and confidence in their work.It is important that nurse educators be effectively capacitated and supported (Waters et al. 2003:516).Lack of mentoring leads to various workplace problems for NANEs.

Problem statement

In order to achieve the goal of transformation, as is expected of higher education institutions, nurse educators must be supported (South Africa 2000: 2).Institutions of higher education in nursing do not have mentoring programmes suitable for nurse educators (Greyling 2003:8).Nurse educators receive induction, which is conducted for all newlyappointed staff, but this does not put emphasis on nursing educators' needs (Booyens 1998:381;Muller 2002:261).On their first day of work, nurse educators mainly receive orientation about the physical layout of the school and/or department and its policies.In institutions where mentoring is practised effectively, mentors who are assigned to NANEs convey their wisdom to their mentees.Mentors are experienced leaders who act as friends and their goal is to create a safe context for academic growth and support for the mentees (O'Brien 2003:10).Mentoring is needed in order to build the capacity of nursing education institutions.

There seems to be no sufficient provision for capacity building in relation to actual teaching, research and community development (Büchner & Hay 1998:2).Research output is rated highly at South African higher education institutions and, consequently, academic writing and publications in accredited journals are important criteria for appointment and promotion.The research function of universities has escalated in size and strength (Büchner & Hay 1998:2).Funding formulae of higher education institutions are based on research output and throughput rates.Therefore, teaching and learning to increase the number of postgraduates in order to increase throughput rates is an additional challenge for academic staff members (Büchner & Hay 1998:20;South Africa 2000:2).Higher education is characterised and challenged by the complexity of content and quality regulation policies, unmet mentoring needs of NANEs and the need to recruit and retain quality nurse educators who can cope with the challenges of higher education (Büchner & Hay 1998:20;South Africa 2000:2).Reyes (2003) supports this idea by indicating that mentoring is a much-needed career development opportunity that socialises NANEs within their higher education institutions whilst simultaneously developing the skills and behaviour of dynamic leaders.

The nature of the problem was revealed by a survey conducted by the researcher which indicated the lack of mentoring programmes at schools and/or departments of nursing at higher education institutions in South Africa.Fifteen (83%) of the 18 (100%) universities responded negatively to the inquiry about the availability of mentoring programmes in their institution; the line managers indicated that such mentoring programmes did not exist.The head of one school of nursing responded telephonically and indicated that she was in the process of developing a programme for the entire Faculty of Health Sciences.Eleven (28%) of the 31 (100%) nursing colleges responded in writing to the question about the availability of mentoring programmes at their institutions.All 11 nursing colleges indicated that they did not have a programme of that nature.Some of the heads of schools and/or departments stated in writing that staff members were exposed to the induction programmes of their universities conducted by their Human Resources Departments together with all other newly-appointed staff.There are no mentoring programmes at these institutions especially for nurse educators.

From the problem statement and the results of the survey it can be deduced that certain needs are apparent amongst NANEs in nursing education institutions in South Africa.

The development of a model to mentor NANEs in nursing education institutions in South Africa, as a possible solution to the highlighted problems, was needed.Thus, the following question can be asked: 'What model can be developed to mentor newly-appointed nurse educators in nursing education institutions in South Africa?'

Aim of the study

The aim of this study was to describe the model for mentoring NANEs in nursing education institutions in South Africa.

Research objectives

The objectives of this study were to develop a model for mentoring NANEs in nursing education institutions in South Africa and to describe the model for mentoring NANEs in these institutions.

Definition of key concepts

Mentoring is when a senior member of an organisation takes on a more junior colleague or may occur between peers, providing a variety of developmental functions.In this study, mentoring is an interactive, reflective, participatory process of relationship building, engagement and development between mentor and mentee during which the former develops and evaluates the achievement of specific development needs in order to achieve the outcome of empowerment and capacity building with regard to specific competencies (Seekoe & Arries 2011:26).

Nursing education is the process whereby learners are guided, assisted and provided with the means which enable them to learn the art and science of nursing so that they can apply this to the nursing care of people who need such care.The ultimate aim of nursing education is the development of highly-skilled professional practitioners as registered nurses (Mellish, Brink & Paton 2009:20).For the purpose of this study, a nursing education institution is a public nursing college or is a department or a school of nursing within universities in South Africa (Seekoe & Arries 2011:26).

A newly-appointed nurse educator (mentee) is a professional nurse who holds a nursing education qualification and is registered with the SANC with that qualification, or is a professional nurse who is registered with the SANC as a general nurse and is in her or his first five years of appointment at a nursing education institution (Mellish et al. 2009:20).For the purpose of this model, a nurse educator is referred to as a mentee who participates in an interactional relationship with a mentor in order to have their mentoring needs met (Seekoe 2009:195).

A model: according to Walker and Avant (2010:126), a model is described as a symbolic representation of empirical experience.In this study, a mentoring model is practice based on the philosophy of reflective practice, competency-based practice and critical social learning theories (Seekoe 2009:186).

Research method and design

A qualitative and theory construction design (Walker & Avant 2010:131) was suitable for the development of the model and was thus used.The process of model development was based on literature review and the findings of analysed needs of NANEs.The analysis of essential concepts was done further through an exploratory factor analysis.The conceptual framework for the mentoring model was developed wherein reasoning strategies of analysis, synthesis, derivation, deduction and induction were applied (Chinn & Kramer 1995:152;Walker & Avant 2010:20), including the experiential knowledge of the researcher (Seekoe 2013:142 ).

Ethical considerations

Ethical considerations, as set out by the Democratic Nursing Organisation of South Africa (DENOSA 1998) in its ethical standards for nurse researchers, were ensured through requesting that participants sign consent and by keeping the participant's information confidential.To ensure privacy and anonymity, the participants and names of institutions were not required in the questionnaires.Self-determination was ensured by allowing participants to withdraw from the study at any time without fear of being punished.Justice was ensured through selecting and treating participants fairly and equally during the study.

The process of model development

The conceptualisation framework for the model focused on the context, content and process (Dickoff, James & Wiedenbach 1968:430) and the theoretical domains that influenced the model.Ideas from different theories were borrowed and integrated with literature.The 'context' represented the nursing education practice environment.The 'intervening factors' are the legal, professional, ethical and practice working environment, healthcare and education of nurses.'Content' refers to the theory of the research domain acquired through literature study on mentoring, the findings of the mentoring needs analysis and essential mentoring needs (conceptual framework); and the 'process' refers to the mentoring needs in nursing education institutions.

Definition and classification of concepts

Identification of concepts was done during literature study and analysis of the descriptive data.Identification of essential needs and concept analysis was done through the performance of exploratory factor analysis where different inferential statistical tests were done and essential mentoring needs were identified.Conceptual meaning was created by considering all sources of literature and experiences related to the concepts under study (Chinn & Kramer 1995:75).Classification of concepts was achieved by using the survey list described by Dickoff et al. (1968:434).Identified concepts were structured within the parameters of integrating theories and models such as stage/identity and transformation theory, contextual dialectical theory, motivation theory and interactional learning theory.Models that were integrated included the critical reflective model (Stuart 2000:700), the three-part dimension model (Schrodt, Cawyer & Sanders 2003:1) and the competency-based model (Wood 2005:39).The survey list of agent, recipient, terminus, framework and procedures was used to clarify concepts.The researcher thereafter classified concepts and determined relational statements.

At this level of theory development, concepts were seen in relation to each other and represented a higher level of complexity.Relationship statements were formulated in order to provide links between and amongst concepts.Tentative relationships were identified.The nature and characteristics of the relationships were discussed.According to Chinn and Kramer (1995:14), the relationship within a theory that creates meaning and impacts understanding often links multiple concepts in a loose structure.These structures emerge from relationships in the theory.The relationship between major or central concepts was clear and individual concepts were structured so as to create greater clarity (Chinn & Kramer 1995:117).

In this study, the context will represent the (framework), the role players (agents and recipients), the purpose (terminus), the process (procedures) and the dynamics (cognitive dissonance around mentoring).The central concepts in the context of nursing education requiring competency development (stakeholders), dependent concepts (the purpose and process of mentoring) and their related constructs will be discussed under each main concept in the model.This will indicate evidence of logical reasoning and consistency throughout the study.

Assumptions of the model

The theoretical framework of this model is based on the philosophy of reflective practice, competency-based practice and critical social learning theories (Stevens 2000:20).The assumptions in relation to stakeholders, context, mentoring, process, outcome and dynamics will be described.

Assumptions related to the context

Mentoring occurs in a context that is multidimensional and highly interactive in nature.In the context of higher education, the mentee is expected to perform according to the quality requirement structures in order to ensure that the political needs of a country -increased numbers of graduates with knowledge and skills to benefit the economy -are met.The legal context includes requirements, where the mentee is expected to ensure quality in teaching, learning and research.The nursing education institution expects the mentee to function according to the performance management policies in order to achieve its vision, mission, values and strategy.At the school and/or departmental level the mentee is expected to teach, research and engage in the community at required specific competencies within the physical and psychosocial dimensions of the mentoring process.

Assumptions related to stakeholders (mentor and mentee)

The mentor and mentee are believed to be holistic beings that function in a psychosocial and cultural environment.They both interact through a participative and interactional relationship to which they commit and where the mentee states their mentoring needs.The mentor displays characteristics that should ensure the success of the relationship, such as acting as a peer and colleague, being available and being a motivator, role-model and capacity builder, which means that the mentee should then feel comfortable interacting with their mentor in a dialogical manner (Wood 2005:39).

Assumptions related to the process of mentoring

Mentoring is believed to be a purposeful directed process of competency development, empowerment and capacity building within an interactive participatory relationshipbuilding process of inquiry, interpretation and dialogue.Throughout the mentoring relationship, a mentor facilitates the ability to inquire and seek new knowledge in order to improve the mentee's performance.A mentor also assists a mentee in developing the skills required to both identify and interpret the requirements and expectations of higher education using reflective practice and by applying constructivism through active exploration.Acquisition of skills of self-inquiry is done under the control of a mentor -a process called scaffolding.The mentor serves as a role model to the mentee.The mentee is allowed to reflect on their practice and to develop learning abilities by constructing a portfolio of evidence.

Assumptions related to the outcome of mentoring

The purpose of mentoring is capacity building, empowerment and development of competencies in order for the mentee to function effectively in their own environment.It is achieved through participatory interaction between a mentor and mentee.

Assumptions related to the dynamic of mentoring

The energy source of this model (see Figure 1) is that motivation and commitment are important for the success of mentoring.Empowerment and capacity building are important for adaptation to a new environment.

Description of the model

A model for mentoring NANEs in nursing education institutions in South Africa will be described according to its structure, showing the context, stakeholders, interactive participatory relationship, mentoring process, outcome, dynamics and its evaluation.

Structure of the model The context

The mentoring model is multidimensional and complex in nature.Various dimensions of the context are indicated amongst the macro (higher education), meso (institution) and micro (department of nursing) levels.The three levels of context are linked and have important influences on the practice of the mentee.The macro context has legal, political and professional framework facets characterised by various legislation that puts demands on the institutions and mentoring of staff.All the structures require competent nurse educators who can produce skilled graduates who will ultimately be employed in the healthcare industry in order to improve service delivery.Mentoring serves the purpose of developing the required competencies of the mentee in order to increase performance which can, in turn, lead to retention.Analysis and clarification of the main concepts of empowerment and capacity building in order to develop competencies and increase the performance of the mentee in the multidimensional context of higher education give the outcome, structure and the process of the model.The environment of the practice of nursing education is influenced by complex factors impacting on one another.The context of higher education impacts on the institutional processes and procedures within which the mentor and mentee function in their relationship.

The meso context (higher education institution) depicted in this model refers to the higher education institution such as the university or nursing college where the mentee is employed.It is made up of elements such as vision, mission and values accompanied by strategy and strategic goals that impact on the mentoring process within that specific institution, as well as performance management strategies and mentoring strategies by which the mentoring performance of both the mentor and mentee are measured.The institution has a unique culture to which the mentee has to adapt and develops governance structures which ensure quality in its delivery of services.The department of human resources is tasked with the responsibility of ensuring that staff increase performance in order to achieve strategic goals.Mentoring is utilised to develop the competencies of the mentee, so that they become competent in teaching, research and community development.

The micro context (department of nursing) in this model refers to the time-spatial situation within which the mentor and the mentee find themselves.This could mean, for example, a nursing department and the relationship between the mentor and mentee.The key stakeholders at this level are the mentor and the mentee.The culture of the nursing department is unique and may be strange to the mentee.The environment itself is physical and psychosocial in nature.The relationship between the mentor and the mentee is interactional and participatory and important in that it is central to the success of the mentee in higher education.A mentor has the role of responding to the needs of mentee, which they do through the process of relationship building, engagement, development and reflection.This process leads to the outcomes of mentoring which are capacity building, empowerment and competency development.The mentee has needs which are stated in the empirical phase of the study and he or she is an active participant in the relationship in that these needs are communicated to the mentor.Both mentor and mentee commit to the relationship.

Stakeholders

Stakeholders are individuals who have a participatory role in a project or a process and, in this case, both the mentor and mentee are important.

Mentor

A mentor is one of the important stakeholders in the success of mentoring and has the role of ensuring that the mentee is empowered, capacitated and academically competent in order to succeed in higher education.A mentoring role is carried out within a participatory interactional relationship with the initial stages of getting established, performing and ending with the mentee.A mentor achieves the outcomes of mentoring through relationship building, development, engagement and reflection.When the two role players work together cooperatively the relationship becomes closer and more successful.

Mentee

A mentee is the most important stakeholder, participating in an interactional relationship with a mentor in order for their own mentoring needs to be met.

Needs

The needs of a mentee are determined based on the empirical data and are grouped into structure, stakeholder, process needs and outcome needs within a participatory interactional relationship throughout the stages of relationship building, development, engagement, reflection and evaluation.The mentee's needs are based on the outcome -such as being empowered, having capacity and feeling competent at the end of the mentoring period.The mentee shows responsibility whilst participating in a mentoring relationship through request and being available to participate in dialogue with a mentor.A mentor challenges the mentee through questions so as to stimulate thinking as a reflective practitioner.

Interactive participatory relationship

Interactional participatory relationship implies that the mentor acts as a peer and that both depend on each other.The success of the relationship is indicated by the development of the mentee's competencies and is demonstrated by a free exchange of ideas between the mentor and mentee.The mentee is engaged through strategies of information sharing, support and benefits.

The mentoring process

Mentoring is an interactive participatory reflective process of relationship building and engagement between the mentor and the mentee, during which the former develops and evaluates the achievement of specific development needs in order to achieve the mentoring outcomes through reflective practice.The mentor drives the process of mentoring through a sequence of activities such as building the relationship, development, engagement and reflective practice until mentoring outcomes, such as empowerment and capacity building to develop required competencies, are achieved.

Relationship building

Relationship building is when the two stakeholders meet and agree to work together toward achieving a mentoring outcome.The relationship develops through stages of initiation, getting established, performing and, ultimately, ending.The initial stage of relationship building starts immediately after induction and is followed by concerns, observation, common characteristics, abilities or recognition of shared values.This stage is identified by signs of carefulness, uncertainty, avoidance of conflict and seeking direction from the mentor.Strategies for managing the stage are closeness and reciprocity, reaching agreements and self-awareness.The stage continues with the signing of a mentoring agreement covering the ground rules and expectations, as well as the frequency of meetings throughout the probation period for whatever period is determined by the institution.

Development

Development means growth, advancement and improvement in the knowledge, skills and attitude of the mentee in higher education.This is the second stage of getting established, characterised by testing the ground and learning their strengths and weaknesses.The qualities of this stage are conflict, power struggle, criticism and challenge.Strategies of success at this stage are a mentoring strategic plan, observation participation and development according to areas of a job description and the use of consultation sessions.The mentor reaches out to the mentee through counselling and encouragement, ultimately becoming a source of psychological support.

Engagement

Engagement is the third stage, taking place when the mentor acts as a role model, communicates, acts as a change agent, empowers, leads, guides and focuses on the mentee's performance.This is a stage of working and training, where each stakeholder accepts one another's weak points, demonstrates a willingness to share knowledge, gives input creatively and is fully committed to the process.There is mutual trust and respect for each other's competence, as well as honest sharing.The mentor engages and challenges the mentee with scenarios and asks questions that are related to practice, identifies weaknesses and offers constructive feedback and support.

Reflective process

This is the final stage of higher order construction where there is evidence that a mentor has developed the mentee through being an independent practitioner, communicator, decision maker, problem solver, networker, change agent and a reflective practitioner with regard to their academic functions (research, article writing, conference presentations and teaching, learning and assessment).The strategies for this stage are making sure that the mentee is capacitated and committed to self-inquiry, uses portfolios of evidence, a reflective journal and diary, has been introduced to power structures and networks, manages change and acts as a reflective practitioner.

Assessment

A mentor uses constructivism to assist the mentee to learn through active exploration and to build new knowledge on the present context of social knowledge of interaction between a mentor and mentee.Acquisition of skills is achieved when a mentee develops required skills through interaction and support by the mentor.This development of an individual's appropriate knowledge and skills is developed until the mentee is in control of them -a process called scaffolding.A mentor carries this role throughout the mentoring relationship.

Mentoring outcome

The outcome of a mentoring relationship is the development of the required competencies characterised by the promotability of the mentee, which is achieved through capacity building and empowerment.Strategies for capacity building are exposure, support and training, whilst empowerment is achieved through networks, hierarchies and professional associations.

Dynamics

The driving factor is motivation.In addition, empowerment and capacity building are key to the success of mentoring.

Evaluation of the model

The model was evaluated in accordance with the guideline criteria for model evaluation laid down by Chinn and Kramer (1995:75) which answered questions as to its clarity, simplicity, generality, accessibility and importance.The model was also evaluated through presentations at national and international conferences and doctoral committees.The researcher used a self-reflective questionnaire in order to evaluate the model under the guidance of expert promoters throughout the study.

Limitations

This research had some limitations in that data from the nursing colleges were not adequate enough to represent the population because of a poor response from the authorities in terms of permission for data collection.

Recommendations

For the practice of nursing education: There is a need to test the guidelines for the operationalisation of the model in the practice of nursing education at universities and nursing colleges.There is also a need for the development of mentoring programmes in nursing education institutions in order to test the application of the model.

For research: It is recommended that a mentoring programme be implemented in order to increase research skills and scholarship in nursing education institutions.

Conclusion

The design and assumptions of the model were discussed, followed by a description of structure.Mentoring takes place in a multidimensional context with three levels: macro (legislation, framework and ethical), meso (governance, strategic, quality assurance and performance-based) and micro (process, competency and stakeholders).The macro level is legal and ethical and is a framework, whilst the meso level is institutional and the micro level is more operational at the school and/or departmental level.Mentoring takes place in a process of relationship building, engagement, development, self-inquiry and reflection.The most important role players are the mentor and the mentee.They relate in an interactive and participative relationship.The outcome of mentoring is empowerment and capacity building in order to develop the competencies of the mentee, which will ultimately increase competencies in higher education.

FIGURE 1 :
1

AcknowledgementsMy sincere gratitude goes to the South African research funding organisations such as the National Research Foundation (NRF) and the Medical Research Council (MRC) with regard to their funding for this study.The UNEDSA Project, funded by Atlantic Philanthropy, is acknowledged for funding to publish this article.I acknowledge the reviewers for giving constructive feedback which contributed to the quality of this publication, as well the participating nurse educators at nursing education institutions in South Africa for responding to the questionnaires and providing support during data collection.Competing interestsThe author declares that she has no financial or personal relationship(s) which may have inappropriately influenced her in writing this article.
Dimensions of nursing management. S W Booyens, 1998Juta Academic PublishersKenwyn2nd edn.

Staff induction: Establishing mentorship programmes for academic staff in South African institutions of higher education. J Büchner, D Hay, South African Journal of Higher Education. 1231998

Theory and nursing: a systematic approach. P L Chinn, M K Kramer, 1995Mosby Year BookSt. Louis, MI4th edn.

Criteria for programme accreditation. 2004The Council on Higher EducationPretoria

Position statements: ethical standards for nurse researchers. 1998South AfricaDemocratic Nursing Organisation of South Africa

Theory in a practice discipline. I. Practice oriented theory. J Dickoff, P James, E Wiedenbach, 10.1097/00006199-196809000-00006Nursing Research. 1751968

Existing abilities and the perceived importance of skill development. G English, J Bonaguro, S Madison, 10.1080/19325037.2005.10608199American Journal of Health Education. 3652005

Promoting high quality performance through mentoring: a programme for higher education. L Greyling, 2003. January 2014JohannesburgRand Afrikaans University

Teaching and learning: the practice of nursing. J M Mellish, H Brink, F Paton, 2009Heinemann PublishersJohannesburg5th edn.

Nursing dynamics. M E Muller, 2002Sandown3rd edn., Heinemann Ltd

Mentors: One solution to high attrition rates. L O'brien, Australian Nursing Journal. 1011372003

The relationship of mentoring to job placement in school administration. A Reyes, 10.1177/019263650308763505NASSP Bulletin. 876352003

An examination of academic mentoring behaviours and new faculty members' satisfaction with socialization and tenure and promotion processes. P Schrodt, C S Cawyer, R Sanders, 10.1080/03634520302461Communication Education. 5212003

Development, implementation and evaluation of a problem-based learning programme for first year nursing students. E Seekoe, 1999BloemfonteinFaculty of Health Sciences, School of Nursing, University of the Orange Free Stateunpublished Masters dissertation

A conceptual framework for a mentoring model for nurse educators. E Seekoe, African Journal for Physical. 192013Recreation and Dance

Academic staff mentoring, curriculum change and client perceptions in higher education. E Seekoe, E Arries, L. Makondo2011. 2011University of Fort Hare Research Book Series1A South African perspective of mentoring needs for newly appointed nurse educators

. Higher Education Act. 1011997. 1997South Africa

Aspects of the work of the teacher committee on teacher education system. 2000PretoriaSouth Africa ; National Plan for Higher Education, Government Printers

. Nursing Act. 332005. 2005South Africa

Mentoring on the cutting edge. K R Stevens, Reflections on Nursing Leadership. 2632000

Models of teacher education. J Stuart, 2000Faculty of Education, University of Johannesburgunpublished Masters thesis

Strategy for theory construction in nursing. L O Walker, K C Avant, 2010Prentice Hall International (UK) LtdLondon5th edn.

Evaluation of a pilot mentoring programme for nurse managers. D Waters, M Clarke, A H Ingall, M Dean-Jones, 10.1046/j.1365-2648.2003.02651.xJournal of Advanced Nursing. 4252003

The importance of principals: site administrators' roles in novice teacher induction. A L Wood, 2005American Secondary Education33