Intense UV long persistent luminescence benefiting from the coexistence of Pr3+/Pr4+ in a praseodymium-doped BaLu2Al2Ga2SiO12 phosphor

Abstract

Phosphors emitting visible and near-infrared persistent luminescence have been extensively studied and commercialized owing to their wide applications in emergency lighting, information storage and in vivo bioimaging. However, ultraviolet (200–400 nm) persistent phosphors are rarely reported. Here, we developed a new Pr³⁺ activated BaLu₂Al₂Ga₂SiO₁₂ persistent luminescence phosphor, which could be effectively excited by a standard 254 nm mercury lamp and exhibits excellent ultraviolet (280–400 nm) persistent luminescence lasting for more than 3 h. This exciting result encouraged us to comprehensively investigate its structural information, photoluminescence and thermoluminescence properties to reveal a feasible persistent luminescence mechanism. The results show that Pr³⁺ ions act as both photoluminescence and persistent luminescence emitters, and the ultraviolet light emission originates from its parity allowed 4f¹5d¹ → 4f² inter-configurational transitions. The suitable energy location of the lowest energy 4f² → 4f¹5d¹ excitation transition and small Stokes shift of less than 3000 cm⁻¹ (0.37 eV) related to the composition and crystal structure of the host lattice BaLu₂Al₂Ga₂SiO₁₂ ensure the occurrence of Pr³⁺ 4f¹5d¹ → 4f² transitions. Moreover, the suitable trapping levels related to Pr⁴⁺ in BaLu₂Al₂Ga₂SiO₁₂:Pr³⁺ were also investigated utilizing thermoluminescence spectra, which could be effectively filled by carriers under 254 nm light irradiation to achieve ultraviolet persistent luminescence. This study opens up new avenues for future research on ultraviolet persistent luminescence and brings new application prospects in the fields of photocatalysis and photodynamic therapy.