Optical and structural characterization of quadruplet and quintuplet molybdenum-containing phosphate glasses

In this work, vitreous samples were prepared in two series by normal melt-quenching technique and under controlled conditions. The amorphous nature of specimens was confirmed using XRD spectra. To perform FT-IR and UV-vis studies, the thin blown films were also prepared. Different ratios of transition metals are assumed to cause depolymerization of the phosphate glass network. Infrared spectra showed absorption bands related to characteristic bonds of phosphate. The P=O bond at about 1200 cm(-1) was observed, as a direct consequence of meta-phosphate bond group. The almost unchanged peak position and intensity of P=O bond (in the presence of two transition metal ions) indicated the glass modifying nature of transition metal oxides (TMOs). The spectra of two series are almost identical, except for 890-1100 cm(-1) range, which can be attributed to presence of second TMO in the first glass series. UV-vis spectra also showed that the absorption edge, optical band gap and Urbach energy of the prepared samples are highly dependent on the kind and percentage of their reagents. The most striking result of UV-vis measurements was increasing and decreasing of optical band gap in the first and the second series with MoO3 content, respectively. The shape of the absorption edge (a plot of (ahv)(1/2) versus hv) demonstrated the indirect nature of the band gap in the prepared specimens.