Insights into the microscopic mechanism of persistent luminescence in Cr3+-doped ZnGa2O4 phosphors

Persistent luminescence (PersL) phenomenon is the result of dynamic distribution of microscopic charges caused by an external field stimulation. A long-standing unresolved question is that why red afterglow phosphors activated by Cr3+ can mainly be obtained in Ga-based compounds. Here, we systematically investigate the ZnGa2O4:0.5%Cr3+,0.5%M3+ (M = Bi, Tb) and ZnGa2O4:0.5%Cr3+ phosphors by a combination of experimental characterizations and first-principles calculations. An enhanced Cr3+ PersL mechanism is proposed based on the regulation of the band gap structure and the redistribution of electron clouds by doping. These changes localize the defect energy levels near the Fermi level, thereby transforming them into effective traps. Additionally, the Cr3+ doping keeps the original ZnGa2O4 rigidity, while enhances physical parameter anisotropy, which provides channels for carrier migration, while suppressing lattice scattering and non-radiative relaxation.These phosphors are further used for high-level anti-counterfeiting. This study firstly reveals that the large anisotropy of physical quantities induced by Cr3+ substitution for Ga3+ is responsible for the strong afterglow effect in Cr-activated Gabased materials.