Conclusions
DTA analysis confirms that incorporation of calcium fluoride (CaF2) into barium phosphate glasses resulting in improvement in both thermal stability against crystallization and glass forming ability. These glasses with improved thermal stability with thermal stability parameter above 100 °C are suitable for fiber fabrication. Optical band gap energy (Eopt) and Urbach energy (Etail) were found to be composition dependent. Calculated theoretical optical basicity (λth) and metallization criterion (M) further confirm the experimental result of increase in optical band gap energy with the increase in CaF2 content. Correlation between average anion polarizability (αO/F) and average optical basicity (λ) was found to be system dependent and linear relation connecting them that can be used for glass system containing both oxides and fluorides (oxyfluoro phosphate glasses) is found to be suitable for the present system of glasses.