UV-A scintillation and persistent luminescence from Ce- and Ce/Ho-doped YPO₄ nanoparticles

Ce³⁺- and Ce³⁺/Ho³⁺-doped YPO₄ nanoparticles were synthesized via a microwave-assisted hydrothermal method to explore their potential as UV-A (320-400 nm) emitting nanoscintillators and persistent luminescence nanophosphors. The as-prepared Ce-doped YPO₄ nanoparticles exhibited nanoporosity, a median size of ∼55 nm, and detectable Ce³⁺ photoluminescence (PL) without the need for high-temperature annealing. Post-synthesis annealing at 1100 °C markedly enhanced both the PL yield and radioluminescence (RL) response, achieving ∼37% of the RL intensity observed in a bulk reference sample. This enhancement was accompanied by a moderate increase in particle median size to ∼68 nm and a loss of nanoporosity. Under X-ray excitation, the annealed nanoparticles demonstrated fast scintillation with a main decay time of ∼27 ns. Co-doping with Ho³⁺ induced persistent UV-A luminescence, supporting the roles of Ce³⁺ as a deep hole trap and Ho³⁺ as a shallower electron trap. Optimal persistent luminescence was observed at nominal Ce/Ho concentrations of 0.5/0.5 mol%. These findings highlight the dual-mode optical functionality of Ce- and Ce/Ho-doped YPO₄ nanoparticles, offering rapid scintillation response and long-lasting emission, respectively. Combined with the already reported structural stability, biocompatibility, and aqueous dispersibility of the YPO₄ nanoparticles, these materials are promising candidates for biomedical applications requiring sustained UV-A emission in deep tissue environments.