Trap Depth Distribution\nDetermines Afterglow Kinetics:\nA Local Model Applied to ZnGa<sub>2</sub>O<sub>4</sub>:Cr<sup>3+</sup>

Persistent luminescence materials have applications in\ndiverse\nfields such as smart signaling, anticounterfeiting, and in vivo imaging.\nHowever, the lack of a thorough understanding of the precise mechanisms\nthat govern persistent luminescence makes it difficult to develop\nways to optimize it. Here we present an accurate model to describe\nthe various processes that determine persistent luminescence in ZnGa<sub>2</sub>O<sub>4</sub>:Cr<sup>3+</sup>, a workhorse material in the\nfield. A set of rate equations has been solved, and a global fit to\nboth charge/discharge and thermoluminescence measurements has been\nperformed. Our results establish a direct link between trap depth\ndistribution and afterglow kinetics and shed light on the main challenges\nassociated with persistent luminescence in ZnGa<sub>2</sub>O<sub>4</sub>:Cr<sup>3+</sup> nanoparticles, identifying low trapping probability\nand optical detrapping as the main factors limiting the performance\nof ZnGa<sub>2</sub>O<sub>4</sub>:Cr<sup>3+</sup>, with a large margin\nfor improvement. Our results highlight the importance of accurate\nmodeling for the design of future afterglow materials and devices.