Investigation on structure and photoluminescence properties of Ho3+ doped Ca3(VO4)2 phosphors for luminescent devices

Abstract

This study focuses on the synthesis and characterization of Ho³⁺ doped Ca₃(VO₄)₂ phosphor for potential application in solid-state lighting technology. A citrate-based sol–gel process is optimized to achieve sheet-like morphologies in the phosphor material. The investigation reveals UV absorption at 371 nm, indicating a band gap of 3.28 eV. Emission transitions at (506, 541, and 651) nm are observed when excited at 451 nm, with an optimal Ho³⁺ concentration of 0.05 mol resulting in robust green emission at 541 nm. The concentration quenching in Ca₃(VO₄)₂:xHo³⁺ phosphors is discussed in detail with Blesse's and Dexter's models. The concentration quenching effect found in the studied samples is due to the dipole–dipole interactions. Judd–Ofelt intensity parameters were calculated from the excitation bands, and for Ω₂, Ω₄, and Ω₆ are (0.16, 0.17, and 0.36) × 10⁻²⁰ cm², respectively. The emission properties for the (⁵S₂ + ⁵F₄) → ⁵I₈ and ⁵F₅ → ⁵I₈ transitions are also estimated with J–O parameters. The higher magnitude of branching ratios (83%) and emission cross-sections (1.6 × 10⁻²¹ cm²) suggest that the Ca₃(VO₄)₂:0.05Ho³⁺ phosphor materials may be suitable for efficient green-emitting device applications. The CIE coordinates confirm the potential of Ho³⁺-doped phosphors for green emissions, making them suitable for solid-state lighting and display technology.