Structural, optical, and Judd-Ofelt spectroscopic analysis of Dy^3 + doped borate-based oxyfluoride glasses exhibiting enhanced UV excitable-yellow luminescence for advanced photonic applications

Dy³⁺ doped borate-oxyfluoride glasses with the composition 50B₂O₃-20SrO-20Li₂O-(10-x)BaF₂-xDy₂O₃ (x = 0–2 mol%) were synthesized using the conventional melt-quenching method and comprehensively characterized to understand their structural and luminescent behaviour. X-ray diffraction confirmed the amorphous nature of all samples, while Pair Distribution Function (PDF) analysis revealed distinct short-range correlations, with B-O and O-O distances at ∼1.25 Å and ∼2.52 Å, respectively, establishing well preserved short-range order. Density and molar volume measurements showed a composition-dependent pattern in which initial structural expansion resulted from the incorporation of heavier Dy³⁺ ions, followed by structural compaction at higher concentrations due to enhanced Dy-O-B cross-linking and network tightening. Diffuse reflectance studies displayed systematic variations in optical band gap (2.70–3.02 eV) and Urbach energy (0.449–0.658 eV), reflecting restricted disorder and increased network rigidity. Refractive indices rising from 2.41 to 2.48 further confirmed enhanced electronic polarizability with Dy³⁺ content. FTIR spectra identified both BO₃ and BO₄ units, and the tetrahedral boron fraction (N₄) decreased from 0.762 (undoped) to 0.514 at 1 mol% Dy₂O₃ due to network depolymerization and increased non-bridging oxygens, then increased to 0.575 at 2 mol% because of Dy-O-B reinforcement. Judd-Ofelt analysis produced intensity parameters Ω₂= 0.361–13.243 × 10⁻²⁰ cm², Ω₄= 4.842–8.828 × 10⁻²⁰ cm², and Ω₆= 2.479–4.777 × 10⁻²⁰ cm², with an optimum spectroscopic quality factor (Ω₄/Ω₆=3.56) at 1.5 mol% Dy₂O₃. Photoluminescence under 351 nm excitation exhibited strong emissions at 482 nm (blue), 577 nm (yellow), and 663 nm (red), with the highest yellow intensity and optimal Y/B ratio at 1 mol% Dy₂O₃ due to enhanced site asymmetry and stronger Dy-O-B coordination. The novelty of this work lies in integrating PDF analysis, FTIR structural chemistry, and Judd-Ofelt radiative modelling to establish a direct structure-property correlation for Dy³⁺ activated borate-oxyfluoride glasses, enabling precise optimization of yellow emission for UV-excitable photonic applications.