Improvement of Near-Infrared Persistent Luminescence in Lithium Substituted MgGa2O4:Cr3+ Nanocrystals

Abstract

Near infrared (NIR) persistent phosphors can exhibit NIR emission for a long period of time after the remove of irradiation, and they have attracted much attention since the demonstration that NIR persistent luminescent nano-sized particles can be used for in vivo imaging. Here, a new NIR persistent luminescence material of lithium substituted MgGa2O4:Cr3+ (termed as MGO:Cr3+, Li+) has been successfully synthesized by sol–gel processing. The MGO:Cr3+, Li+ mainly consists of ∼40–100 nm nanocrystals, which are of single crystalline with excellent crystallinity. Li+ ions occupying the tetrahedral sites (Mg site) does not significantly affect the crystal structure, but it induces a broader band gap. In the processing of substitution for the Mg2+ site by Li+, oxygen vacancies appear that can efficiently store the excited electrons by UV light irradiation and contribute to the improved persistent luminescence. Mg vacancy arising from a higher calcination temperature tends to store visible light, which also contributes to the enhanced afterglow intensity.