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

Abstract

A series of P<inf>2</inf>O<inf>5</inf>–B<inf>2</inf>O<inf>3</inf>–BaO glass system containing various V<inf>2</inf>O<inf>5</inf> and TiO<inf>2</inf> 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<inf>?</inf><g<inf>?</inf><g<inf>e</inf>) 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 [VO<inf>4</inf>]3- groups and Ti3+ ions significantly enhancing emission properties. The enhanced luminescence was observed for glasses with 0.75 mol% TiO<inf>2</inf> and 0.75 mol% V<inf>2</inf>O<inf>5</inf>. Notably, the 0.75 mol% V<inf>2</inf>O<inf>5</inf>-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. © 2025 Elsevier B.V.