Influence of low concentrations of vanadium and titanium ions on the structural and optical properties of borophosphate glasses

A series of P₂O₅–B₂O₃–BaO glass system containing various V₂O₅ and TiO₂ content (from 0.25 to 0.75 mol%) were synthesized using the melt-quenching method to examine their structural, EPR, and optical characteristics. EPR analysis confirmed VO²⁺ hyperfine splitting and the presence of Ti³⁺ ions in a tetragonally compressed octahedral structure. The local structures of VO²⁺ and Ti³⁺ centers were explored through spin Hamiltonian parameters ($g_{\parallel }<g_{\perp }<g_e$) and optical transition energies. UV–visible spectroscopy revealed multiple oxidation states of vanadium (V³⁺, VO²⁺ and V⁵⁺) and titanium (Ti³⁺, Ti⁴⁺), which significantly influenced the optical characteristics. Photoluminescence (PL) studies indicated the presence of oxygen vacancies and intrinsic defects in the glass matrix, with [VO₄]^3- groups and Ti³⁺ ions significantly enhancing emission properties. The enhanced luminescence was observed for glasses with 0.75 mol% TiO₂ and 0.75 mol% V₂O₅. Notably, the 0.75 mol% V₂O₅-doped glass, exhibited CIE chromaticity coordinates (x = 0.26, y = 0.31), closely aligning with standard white light. The tunability of optical properties through transition metal oxide doping highlights the potential of these glasses for advanced photonic applications, including optical filters and display technologies.