Physical, structural and optical characterization of silicate modified bismuth-borate-tellurite glasses

• SiO2 is present in SiO4 tetrahedral structural units with two NBOs per silicon.
• Bi2O3 is present in both BiO6 octahedral and BiO3 pyramidal structural units.
• HEM shows good agreement with the experimental observed absorption spectra.

The quaternary glass system xSiO2-(80-x) Bi2O315B2O35TeO2 has been prepared by melt-quench technique. The amorphous nature of glass samples has been ascertained by X-ray diffraction patterns. The variations in density, molar volume and crystalline volume with glass compositions have been discussed. A non-linear change has been observed in glass transition temperature and optical band gap energy. Raman and FTIR spectral studies suggest that glass network is mainly built up of BO3, BO4, SiO4, and TeO3 structural units, whereas BiO3 exists as both network modifying [BiO6] octahedral as well as network forming [BiO3] pyramidal structural units. The values of optical band gap energy have been estimated from fitting of both Mott and Davis's model and Hydrogenic excitonic model (HEM) with experimental data of absorption spectra. The HEM model shows good agreement with experimentally observed absorption spectra, which indicates the exciton formation in studied glass system. The non-linear compositional change in optical band gap energy is related with the structural changes occurring in present glass samples. The Urbach energy has also been estimated. The range of metallization criterion suggests that prepared glasses may be considered as new nonlinear optical materials.