Self-activated LiGa5O8 storage phosphor: The insights into photo/thermo/mechano-stimulated NIR Luminescence

Multi-mode storage phosphors with photo/thermo/mechano-stimulated luminescence (PSL/TSL/ML) hold great potential applications in many fields such as biological imaging, human-machine interface, robotic manipulation, and stress/temperature visualization sensing. However, the physical mechanisms underlying this 'self-sustaining' luminescence are still debated, which in turn hinders the development of materials. Here, we demonstrated that the intrinsic defects such as the VO•• and Oi′′ in the matrix play an important role in the electronic structure and various physical properties of LiGa5O8 storage phosphor by combining first-principles calculations and experimental methods. Specifically, the intrinsic defects lead to the smaller bulk (B) and shear (G) modulus, Young’s moduli (E), Poisson’s ratio (v), B/G, and the bigger elastic anisotropy index (AU) and hardness (H) in three LiGa5O8 defect models, which is extremely advantageous for PSL/TSL/ML. We also demonstrate that the ML process, that is different from PSL/TSL processes, are intimately linked to the activation threshold of charge carriers in traps. This threshold can be lowered under axial stress by bandgap narrowing via weakening the binding force of polyhedral units to bind electrons in the converting process between mechanical energy and light energy under stress load. This study provides not only direct evidence for potential variation in ML process, but also guidance for designing the storage phosphors via defect engineering.