The optical transmittance spectra are plotted in Fig. , while average transmittance values are listed in Table . As observed, the films are highly transparent in the visible range (above 50%). The refractive indices of all fabric samples were approximately 1.51. As the film thickness increased, the average transmittance decreased due to the thickness effects. In general, the excited Zn6O6 cluster (as seen in the bond lengths reaching differences of up to 5% when compared with ground-state geometries) is more distorted than the Zn6S6 clusters. These results, therefore, suggest a greater increase in the ionic bond character of excited Zn6O6 cluster. To confirm these findings, QTAIM calculations were performed for both Zn6O6 and Zn6S6 clusters. It is important to observe that for the ionic bond: ∇ 2 ρ(r) > 0; -G/V > 1; G+V > 0 and for the covalent bond: ∇ 2 ρ(r)< 0; -G/V < 1; G+V < 0 . The purpose here was to examine the chemical Zn-O and Zn-S bonds to investigate the covalent/ionic character.