Structural and optical properties of bismuth borosilicate glasses: Effect of CeO2 doping

A series of CeO2 doped (0, 0.2, 0.4, 0.6, 0.8 and 1.0 mol E_opt ) were evaluated using Tauc plots and were compared with the one obtained from extinction coefficient versus energy plots. Differential method based on Davis and Mott model was further employed to determine the type of electronic transition mechanism. It is observed that the optical band gap in present glasses arises due to direct forbidden transitions, i.e., γ = 3/2; which is found to be in close agreement with the band gap values extracted from experimental data of absorption coefficient. Analysis of FTIR spectra revealed the existence of mixed borate-silicate linkages (B-O-Si bonds) in addition to trigonal BO3 and tetrahedral BO4 groups. Further, the inclusion of CeO2 is observed to facilitate the transformation of BO4 to BO3 units accompanied by an increase in the concentration of non-bridging oxygens (NBOs) in the glassy matrix. The structural changes observed in the present glasses are discussed in terms of reported decrease in the optical band gap values by making a correlation between FTIR and UV–visible studies.