Comparative spectroscopy study of TeO2–B2O3 glass system for photonic application: barium and bismuth as modifier

In this paper, the spectroscopic characteristics of two series of TeO2–B2O3 glass systems which were successfully synthesized using the conventional melt quenching method were investigated. The compositions of these two glass series are: [(TeO2)70 (B2O3)30]100-x (Bi2O3)x, and [(TeO2)70 (B2O3)30]100-x (BaO)x,. The effects of adding Bi2O3 and BaO on the structural and optical properties of the glass system were studied. The results demonstrate that the boron–boron separation decreases as the Bi2O3 and BaO content increases, as the glass modifier has a higher molecular weight than the glass network TeO2–B2O3. The shifts in the absorption peak shown in the FTIR spectra are dependent on the glass composition. The analysis shows that the structural units, TeO3, TeO4, TeO6, BO3 and BO4, are found in the glass sample. The optical band gap energy, Eg, calculated from Tauc’s plots, decreases as more Bi2O3 and BaO are added. In contrast, the Urbach energy value rises, implying that more defects exist in the glass structure. Both the absorption edge shift into higher wavelength and the decrease in the Eg values were attributed to the restructuring of the glass network and modifier. The shift was also enhanced by the progressive increase in the concentration of non-bridging oxygen atoms. Due to the high polarization and density of the host material and glass modifiers, the refractive indices were also observed to increase with higher content of Bi2O3 and BaO. Despite the fact that the results of the two glasses showed relatively similar trends, the study concluded that Bi2O3 glass is preferable for photonic applications.