Trap depth distribution determines afterglow kinetics: a local model applied to ZnGa2O4:Cr3+

Persistent luminescence (PersL) materials have applications in diverse fields such as smart signaling, anticounterfeiting, and in vivo imaging. However, the lack of a thorough understanding of the precise mechanisms that govern PersL makes it difficult to develop ways to optimize it. Here we present an accurate model to describe the various processes that determine PersL in ZnGa2O4:Cr3+ (ZGO:Cr), a workhorse material in the field. A set of rate equations has been solved, and a global fit to both charge/discharge and thermoluminescence measurements has been performed. Our results establish a direct link between trap depth distribution and afterglow kinetics and shed light on the main challenges associated with PersL in ZGO:Cr nanoparticles, identifying low trapping probability and optical detrapping as the main factors limiting the performance of ZGO:Cr, with a large margin for improvement. Our results highlight the importance of accurate modeling for the design of future afterglow materials and devices.