XRD patterns of 0, 5, 10, 20 and 33EuZnO sponges heated for 3 minutes at 600 and 650 o C, respectively, are shown in Figure . The corresponding unit cell-parameters are given in Table . It can be observed that the diffractograms obtained after heating sponges with compositions of up to 33Eu to 600 and 650 o C, respectively, were quite similar in showing h-ZnO:Eu as the only identifiable crystalline phase. Very broad and overlapping peaks at ~28.6 and ~29.7 o 2θ came up stronger while the ZnO:Eu peaks were strongly reduced in intensity with increased Eu-loading. The broad peaks are associated to the non-periodic [EuO1.5]n clusters. The 33Eu sample showed very weak h-ZnO peaks overlapping the broad peaks which prevented unit cell-parameters to be extracted. The unit cell-parameters of the Eu-doped h-ZnO:Eu phase were very similar for the two synthesis temperatures, differing in the a/band c-axis lengths only by < 0.003 Å, which is within the error of the determination for samples made with the same Eu-loading. The pure ZnO sample showed a larger difference in unit cell-parameters between the samples heated at 600 and 650 o C, which might be due to an easier relaxation of the lattice while removing defects when there are no Eu-oxide clusters present. IR spectra obtained in the mid-and far-IR range of 0-33Eu nano-sponges heated at 650 o C are shown in Figure left and right, respectively. The IR spectra of ZnO:0-20Eu nano-sponges heated at 600 o C were very similar to those obtained after heating at 650 o C indicating small differences in contents and structure. The 33Eu sample heated at 600 o C differed in the presence of weak multiplet bands around 1060 and 1240 cm -1 which were absent in the sample heated at 650 o C. All samples showed weak peaks at 1580-1300 cm -1 , assigned as due to symmetric and asymmetric C-O stretching in Eu-oxo-carbonate, along with water bending modes at 1640 cm -1 . The very weak peak at 840-860 cm -1 is also associated to the carbonate group. These water and carbonate peaks were quite weak compared to the main Zn-O vibration peak at ~390 cm -1 . The water and carbonate are likely formed by absorption H2O and CO2 from the atmosphere, although very minor amounts of internal Eu-oxo-carbonate remaining from the lower synthesis temperatures cannot be excluded. This applies especially to the 33Eu sample which showed somewhat more intense and differently shaped carbonate peaks, compared to the 0-20Eu samples. The Zn-O vibration band ranging from 600 to 300 cm -1 with a maximum at ca. 390 cm -1 was significantly reduced in intensity with increased Eu-content. In addition to the peak assigned to various Zn-O vibrations, a broad band was observed at 350-200 cm -1 which increased in relative intensity with Eu content, especially when comparing the 0-10Eu samples with the 20Eu and 33Eu samples. This band is assigned mainly to Eu-O vibrations in a non-crystalline state.