Zn3Ga2Ge2O10:Cr3+ Uniform Microspheres: Template-Free Synthesis, Tunable Bandgap/Trap Depth, and In Vivo Rechargeable Near-Infrared-Persistent Luminescence

Near-infrared (NIR) emitting persistent phosphors of Cr3+-doped zinc gallogermanate have emerged for in vivo bioimaging with the advantage of no need for in situ excitation. However, it is challenging to synthesize well-dispersed and uniform spherical particles with high brightness, high resolution, and distinguished NIR long afterglow. In this work, Zn3Ga2Ge2O10:Cr3+ (ZGGC) monospheres were directly synthesized by a facile hydrothermal method with the assistance of citric anions (Cit3–), which emit an NIR emission at ∼696 nm and exhibit excellent NIR-persistent luminescence with rechargeability. Controlled experiments indicated that the shape evolution of the ZGGC product is significantly affected by Cit3–, solution pH, and the duration and temperature of hydrothermal reaction. Furthermore, compositional influence on the crystal structure, bandgap, trap depth, and luminescence characteristics of ZnyGa2Ge2O10−δ:Cr3+ (y = 2.8, 3.0, 3.2) were investigated in detail, which allows us to construct an energy le...