Three main thermal parameters such as glass transition temperature, Tg, onset crystallization temperature, Tx and melting temperature, Tm were obtained using an EXSTAR 6200 thermo-gravimetric analyzer/differential thermal analyzer (TG/DTA). Measurement was carried out under nitrogen atmosphere with a flow rate of 300 mL/min in the temperature range from ambient to 1000 °C at a heating rate of 10 °C/min. The crystalline phase of samples heat treated at 600 °C was identified using JEOL JDX-8P-X-ray diffractometer with Cu–Kα radiation. X-ray tube was operated at 40 kV and 30 mA. X-ray diffraction (XRD) patterns of powdered samples were obtained in the diffraction angle (2θ) range of 10°–80° at a scanning rate of 2°/min. Refractive indices of fine polished samples were measured at room temperature using an Abbe (MAR-33) refractometer with an accuracy of ± 0.001. Mono-bromo naphthalene was used as the contact layer between the glass and refractometer prism. Measurements were carried out for two specimens of each composition and the average value of refractive index was obtained. Optical absorption spectra of glass specimen of thickness 1.00–1.20 mm were recorded in the 200–850 nm wavelength range using fiber optic spectrometer USB4000 (Ocean Optics Inc., USA). Thickness of glass specimen was measured using a micrometer with an accuracy of 0.01 mm.