NaPO 3 ‐Modified Sb 2 O 3─ WO 3 Glasses: Structural and Optical Insights for Photonic Applications

ABSTRACT The relationship between structural units and optical properties in Sb 2 O 3─ WO 3─ NaPO 3 glasses was systematically investigated using Raman and Fourier‐transform infrared (FTIR) spectroscopy. FTIR analysis revealed that structural evolution is primarily associated with a reduction in non‐bridging oxygens (NBOs) linked to hydrogen‐bonded hydroxyl groups and a corresponding increase in bridging oxygens (BOs), reflecting enhanced network polymerization. Complementary Raman spectroscopic data confirmed progressive increases in average cross‐link density and network bonds per unit volume, attributed to the formation of P─O─M (M = Sb, W, or P) structural linkages within the glass matrix. With increasing NaPO 3 concentration, the optical absorption edge exhibited a pronounced blue shift, resulting in an enlarged optical band gap (2.47–3.07 eV) and reduced Urbach energy (0.144–0.121 eV), indicative of decreased structural disorder. The derived optical parameters demonstrated systematic compositional dependence: refractive index ( n = 2.45–2.56), molar refractivity ( R m = 23.43–32.90 cm 3 ·mol − 1 ), and third‐order nonlinear susceptibility ( χ ( 3 ) = 5.09–13.09 × 10 − 1 2 esu). Hydroxyl content analysis revealed OH concentrations ranging from 38.28–144.08 ppm, exhibiting an inverse correlation with network connectivity; compositions with higher cross‐link density demonstrated reduced hydroxyl incorporation. Glass transition temperatures ( T g = 290–374°C) increased progressively with phosphate content, reflecting enhanced network rigidity. These favorable structural and optical characteristics establish antimony–tungsten–phosphate glasses as promising candidates for nonlinear optical and photonic applications.