Tailoring trap depth distributions in ZnGa2O4: Cr3+ nanoparticles for optimized persistent luminescence across various functional temperature ranges

Persistent phosphors have attracted significant attention for their potential application in safety signage, road markings, data storage, anti-counterfeiting technologies, and biomedical fields. However, despite the significant advancements in room-temperature persistent phosphors and deep-trap materials for information storage, development of low-temperature persistent phosphors with strong afterglow emission remains a considerable challenge. In this study, we successfully modified the trap depth distribution in ZnGa 2 O 4 : Cr 3+ nanoparticles (ZGO:Cr NPs) by carefully controlling the synthesis conditions in order to develop nanoscale persistent phosphors tailored for various temperature-dependent applications. ZnGa 2 O 4 : Cr 3+ nanoparticles were synthesized via a rapid, facile, and environmentally friendly microwave-assisted hydrothermal method. A subsequent thermal treatment at temperatures of 500 and 700 °C was employed to further modify their structure and, consequently, their optical properties. Notably, the ZGO:Cr NPs without any subsequent calcination (ZGO MW) exhibit strong and long-lasting luminescence at cryogenic temperatures (15 – 200 K) and they show great potential for applications requiring continuous cooling at liquid nitrogen temperatures, such as the cryopreservation of biological agents, viruses, and tissues. In contrast, ZGO:Cr NPs calcined at 700°C (ZGO 700) demonstrate stabilization of deeper traps, with activation energies near room temperature, which shows promise for conventional persistent luminescence applications requiring small particle sizes (<10 nm). Meanwhile, ZGO:Cr NPs calcined at 500°C (ZGO 500) display a broad distribution of traps and a remarkably wide operational range (15–400 K), due to the coexistence of multiple Cr 3+ environments, making it highly suitable for applications requiring stable persistent luminescence behaviour at very wide range of temperatures. • Development of low-temperature persistent phosphors remains a considerable challenge • ZnGa 2 O 4 : Cr 3+ NPs were synthesized via rapid microwave-assisted hydrothermal method • Post-synthesis calcination was used to optimise their structure and modify optical properties • Trap depth tailoring was achieved to develop materials for applications at various temperatures