Structural and optical properties of Nd3+-doped Al-Ca-Na-borosilicate glasses: Judd–Ofelt analysis and spectroscopic investigation

Nd 3+ -doped Al-Ca -Na borosilicate glasses with the composition 58 B 2 O 3 –10 SiO 2 – (14−x) Na 2 O –10 CaO–8 Al 2 O 3 –x NdCl 3 (x = 0–0.8 mol%) were synthesized via the conventional melt–quenching technique. The effects of Nd 3+ incorporation on the structural, physical, and optical properties of the glasses were systematically investigated. Density measurements revealed a gradual increase with Nd 3+ concentration, while the molar volume decreased, indicating network compaction. FTIR spectra confirmed modifications in the borate–silicate glass network, suggesting enhanced BO 4 related features with Nd incorporation. UV–Vis–NIR absorption spectra exhibited eleven characteristic 4f–4f transitions of Nd 3+ ions with a prominent hypersensitive band at 582 nm. The optical band gap (direct and indirect) decreased with higher Nd 3+ content, whereas Urbach energy increased, reflecting enhanced structural disorder and localized defect states. Judd–Ofelt analysis was employed to determine the intensity parameters Ω 2 , Ω 4 , and Ω 6 , which provided insights into the local symmetry and bonding nature around Nd³⁺ ions. Emission spectra revealed strong photoluminescence bands at 900, 1060, and 1330 nm originating from the 4 F 3/2 excited state, with maximum emission intensity observed at 0.6 mol% Nd 3+ before concentration quenching effects became significant. The radiative transition probabilities, branching ratios, stimulated emission cross-section and lifetimes are evaluated.