Raman spectra and optical properties of selected Bi2O3–PbO–B2O3–GeO2 glasses

Glasses of the system (Bi2O3)0.2(PbO)x(B2O3)0.8−2x(GeO2)x, where x = 0.05, 0.1, 0.2, and 0.3, were prepared and investigated. With increasing x, both the density (ρ) and molar volume increased from 5.85 g/cm3 to 7.02 g/cm3 and from 27.06 cm3/mol to 29.25 cm3/mol, respectively, while the dilatometric glass-transition temperature (Tg) decreased from 448 °C to 385 °C. Raman spectra showed that with increasing x, the number of groups based on trigonal boron raised and also increased the amount of various three body linkages which enhanced a structural disorder. From the measurements of the optical transmission on very thin glassy samples, the optical energy gap values (Eg, 300 K) were determined in the range 3.60 (x = 0.05)–3.46 eV (x = 0.3). The temperature dependence of the optical energy gap (Eg(T)) in the region 300–600 K was examined and approximated by the linear relation in the form of Eg(T) = Eg(0) − γT, where γ × 10−4 (eV/K) varied from 4.43 to 5.6. Non-linear refractive index (n2) was estimated at around 8.15 × 10−12 (esu) from the optical energy gap values.