Prediction of glass‐forming regions in AlF3‐M(PO3)2‐R2SO4‐based poly‐anionic fluoro‐sulfo‐phosphate glasses

Phosphate glasses have garnered significant attention as host materials for various laser applications due to their high rare‐earth ion solubility, large stimulated emission cross‐section, and low nonlinear refractive index. Modification of phosphate glass composition is feasible through poly‐anion substitution, leading to poly‐anionic glasses with unique properties. This study explores the glass‐forming regions (GFRs) of AlF3‐R2SO4‐M(PO3)2‐based poly‐anionic fluoro‐sulfo‐phosphate (R/M‐FSP) glasses, a promising class of ionic glasses. Theoretical GFRs are predicted using a thermodynamic approach and then validated through a few experiments. The experimental GFRs range from K/Ba‐FSP > Na/Ba‐FSP > Li/Ba‐FSP > K/Sr‐FSP > Na/Sr‐FSP > Li/Sr‐FSP, with wider areas observed under lower cation field strength. Notably, the K/Ba‐FSP glass system exhibits high anti‐crystallization stability (approximately 140°C) and a low nonlinear refractive index (1.43 × 10–13–1.83 × 10–13 esu), advantageous for high‐power laser operations. Furthermore, a comparative study among K/Ba‐FSP glasses elucidates the general principles of manipulating glass structure and physical properties through compositional variation.