Influence of Pr₆O₁₁ Concentration on the Thermal, Structural, Physical, and Optical Behavior of SNW Glass Systems

Praseodymium-doped antimony-phosphate glasses with the composition 47.5Sb₂O₃-47.5NaPO₃-5WO₃-xPr₆O₁₁ (x = 0.05, 0.1, 0.25, 0.3 mol%) were synthesized by melt-quenching and characterized by DSC, FTIR, density, hardness, ultrasonic, and UV-Vis techniques. T_g (314.26°C-320.61°C) and ΔT (40.12°C-59.07°C) showed limited variation, with highest stability for the undoped glass. FTIR confirmed phosphate groups (P-O-P, PO₃ ^2-, PO₂ ^-) and increasing NBO, indicating Pr-induced depolymerization. Density decreased (4.2735-4.2223 g/cm³), while hardness increased (254-289 kg/mm²). Molar volume (48.47-49.76 cm³/mol), oxygen molar volume (16.16-16.40 cm³/mol), and molar refraction increased, reflecting a more open, polarizable structure. Elastic moduli increased up to 0.25-mol% Pr then slightly decreased. The optical band gap decreased (3.079-3.022 eV), Urbach energy increased (0.350-0.374 eV), and refractive index increased with Pr content. The results indicate that Pr₆O₁₁ functions as an effective network modifier, promoting controlled depolymerization and enhanced optical tunability while preserving thermal stability and mechanical integrity. Among the studied compositions, 0.25-mol% Pr₆O₁₁ provides the optimal balance between structural rigidity, optical properties, and mechanical strength, making these glasses promising candidates for composition-tunable active photonic media, particularly in broadband optical amplifiers, visible-near infrared solid-state laser hosts, and high-refractive-index waveguide components, where the combined enhancement of refractive index, mechanical strength, and electronic polarizability enables efficient light confinement and emission control.