Prolonged Red Persistent Luminescence in Bi³⁺ Single-Doped LiGa₅O₈: Regulating Traps by Site Selective Occupation

Persistent luminescence (PersL) materials with impressive superiorities in optical performance have shown tremendous potential for information encryption application. Herein, a Bi³⁺-doped LiGa₅O₈ PersL material is facilely synthesized by a simple solid-state reaction. Site selective and preferential occupation of Bi³⁺ ions at distinct Ga³⁺ and Li⁺ polyhedra sites in LiGa₅O₈ endows it with a bimodal emission at 511 and 718 nm upon UV excitation at 254 nm. After removing the light source, an intense red afterglow was observed due to the generation of more and deeper traps classified as the oxygen vacancy defect (V_O^••) and the impurity defect (Bi_Li^••). It is rarely reported in inorganic phosphors to achieve the Bi³⁺ single doping-activated red PersL. The LiGa₅O₈:x% Bi³⁺ (with x = 0.5-5.0) samples also exhibit tunable PL and time-dependent PersL properties. Combined with the Morse Code, a multiple information encryption model based on the abnormal optical properties of LiGa₅O₈:x% Bi³⁺ (x = 0, 0.5, and 5.0) samples was designed for high-level dynamic anticounterfeiting. These achievements further validate the use of the Bi³⁺ single doping strategy to explore excellent PersL materials and expand their multifunctional optical applications.