Structural, physical, and luminescence properties of sodium–aluminum–zinc borophosphate glass embedded with Nd³⁺ ions for optical applications

Sodium–aluminum–zinc borophosphate (SAZBP) glass systems doped with varying concentrations of Nd 3+ ions (0–6 wt%) were synthesized via the conventional melt-quenching technique to systematically investigate their physical, structural, and optical properties. The influence of Nd 3+ doping on the glass matrix was comprehensively evaluated through density measurements, molar volume, and ion concentration, revealing a linear correlation between dopant concentration and compactness of the glass network. X-ray diffraction patterns confirmed the amorphous nature of all compositions, while Fourier-transform infrared spectroscopy elucidated structural modifications, including the evolution of BO 3 , BO 4 , and PO 4 units, as well as the formation of non-bridging oxygens with increasing Nd 3+ content. Optical studies revealed a tunable refractive index (1.522–1.529) and Urbach energy, with absorption spectra exhibiting characteristic Nd 3+ transitions ( 4 I 9 / 2 → 2 P 1 / 2 , 4 G 5 / 2 , etc. ). The optical band gap ( E g ) decreasing with higher Nd 3+ concentrations, attributed to the polaronic effect and structural rearrangements. Photoluminescence spectra displayed intense emission at 1,062 nm ( 4 F 3 / 2 → 4 I 11 / 2 ), with Judd-Ofelt analysis yielding intensity parameters ( Ω 2 , Ω 4 , Ω 6 ) that reflect the local asymmetry and covalency around Nd 3+ ions. High radiative transition probabilities ( A rad ), branching ratios ( β > 50%), and stimulated emission cross-sections ( σ emi ) suggest the potential of Nd 3+ -doped SAZBP glasses for near-infrared lasers, optical amplifiers, and photonic devices. The results underscore the role of Nd 3+ in tailoring the functional properties of borophosphate glasses for advanced optoelectronic applications.