Physical, structural and optical characterizations of borate modified bismuth–silicate–tellurite glasses

Abstract Quaternary bismuthate glasses with compositions x B 2 O 3 –(80 −  x ) Bi 2 O 3 –15SiO 2 –5TeO 2 have been prepared by melt-quench technique. X-ray diffraction studies were performed to ascertain the amorphous nature of samples. The density, molar volume and crystalline volume decrease with increase in B 2 O 3 content whereas the glass transition temperature shows the reverse trend. The Raman and FTIR spectra of the studied glasses indicate that B 2 O 3 has been found to exist in the form of BO 3 trigonal and BO 4 tetrahedral structural units and vibrations corresponding to these structural units increase with increase in B 2 O 3 content. SiO 2 is present in the form of SiO 4 tetrahedral structural units and TeO 2 in the form of TeO 3 structural units. Bismuth plays the role of network modifier [BiO 6 octahedra] as well as network former [BiO 3 pyramids] for all the glass compositions. The optical band gap energy has been calculated from the fitting of both Mott and Davis’s model and Hydrogenic excitonic model with the experimentally observed absorption spectra. A good fitting of experimental data with HEM indicates the excitonic formation in the studies glass system. The values of optical band gap energy show nonlinear behavior due to the structural changes that take place in the present glass samples. The Urbach energy calculated using Urbach empirical formula for studied glass samples suggest the possibility of reduction in defect concentrations. The metallization criterion of the presently studied samples suggests that the prepared glasses may be potential candidates for nonlinear optical applications.