Optical band gap, glass transition temperature and structural studies of (100 − 2x)TeO2–xAg2O–xWO3 glass system

Optical absorption, differential scanning calorimetry (DSC) and Raman studies have been carried out on (100 − 2x)TeO2–xAg2O–xWO3 (7.5 ≤ x ≤ 30) glass system. The Raman spectra showed that the structure of glass network consists of [TeO4], [TeO3]/[TeO3+1], [WO4] units. The glass transition temperature (Tg) values were measured from DSC thermogram and the variation in Tg has been discussed in terms of physical parameters like number of bonds per unit volume (nb), average cross-link density (nc¯), average stretching force constant (F¯), oxygen molar volume (Vo) and oxygen packing density (OPD) values. The cut-off wavelength (λc), optical band gap (Eopt), Urbach energy (ΔE) and refractive index (n) values were calculated from optical absorption data. The observed decrease in optical band gap (Eopt), Urbach energy (ΔE) and increase in refractive index (n) values have been discussed in terms of structural changes brought about by WO3 and Ag2O incorporation in to TeO2 network.