Controlling a defect structure of the ZnGa2O4:Cr3+ spinel through synthesis parameters for persistent luminescence optimization

ZnGa2O4:Cr3+ (ZGO:Cr) is one of the most promising red persistent phosphors for in-vivo imaging due to its 650–750 nm emission band in the range of the so-called first biological window. In this paper, we report on how to control the high brightness persistent luminescence of the smallest ZGO:Cr nanoparticles by optimization of hydrothermal synthesis parameters. The influence of pH solution, the temperature of synthesis, and calcination on the degree of inversion, lattice parameters, morphology, and crystallite size were systematically investigated. The results have shown that different synthesis conditions modify the trap depths distribution, by mixing the occupancy of Zn2+ and Ga3+ sites in the spinel structure, which affects the duration and intensity of persistent luminescence. The correlation between structural changes and optical properties is established and it is possible to control them by selecting the appropriate hydrothermal synthesis parameters.