Mechanism of Bi3+ role selection in multi-ion-doped persistent phosphors

Long persistent luminescence (PersL) materials serve as core functional materials in diverse cutting-edge fields including spectroscopy, photochemistry, photonics, materials science, and energy storage/conversion, underpinning the development of key technologies in these domains. However, the fundamental mechanisms governing the interactions between trap states and luminescent centers remain poorly understood, hindering the rational synthesis of high-performance PersL materials and relegating it largely to inefficient trial-and-error. Herein, we developed a series of NaGdGeO 4 :Bi 3+ ,Ln 3+ (Ln = Eu, Sm, Pr) phosphors that exhibit multi-color PersL. Notably, by monitoring PersL emissions from distinct luminescent centers such as Bi 3+ and Ln 3+ within a single phosphor, we observe that thermoluminescence profiles depend on the specific luminescent centers involved. Guided by the bistability of luminescent centers and their energy-level matching with trap states in the host matrix, we propose a phenomenological theory defining luminescent centers as effective PersL centers. Our study deepens the understanding of mechanisms and provides a theoretical framework for designing next-generation PersL materials.