Anomalous Optical Properties of xSrO-10PbO-(90-x)B2O3 Glass System

Raman and UV-Vis spectral analysis of xSrO-10PbO-(90 - x)B2O3 glasses were carried out to elucidate the structural and optical behaviour due to borate anomaly. Raman analysis revealed that the glasses consisted of mainly trigonal groups (metaborate) and tetrahedral groups (ditri/dipentaborate and diborate) at lower SrO content. Concentration of diborate groups reached a maximum value at x = 30 mol% and were replaced by pyroborate, metaborate and orthoborate groups as SrO content in the glass increased. Maximum value of optical band gap (E (opt) ) and minimum values of electronic polarizability (alpha(O2-)), optical basicity (I >) and refractive index (n) were obtained when x = 25 mol%, which was lower compared to maximum of diborate group (x = 30 mol%) as observed from Raman spectroscopic analysis. Observed mismatch in diborate groups and E (opt) maxima was attributed to the formation of weak coordinated covalent bonds during structural transformation and addition of cation with high polarizability to the xSrO-10PbO-(90 - x)B2O3 glass.