Tunable trap depth in Zn(Ga1−xAlx)2O4:Cr,Bi red persistent phosphors: considerations of high-temperature persistent luminescence and photostimulated persistent luminescence†
Thermoluminescence peaks for Cr3+ emissions shift to higher temperature due to the partial substitution of Al for Ga sites in ZnGa2O4:Cr,Bi phosphors, which indicates that the electron traps responsible for the red persistent luminescence are tuned to deeper levels by Al-doping. Al-containing phosphors with deeper traps showed a lower persistent luminescence intensity than Al-free samples at 20 °C because the ambient thermal energy is too low to release trapped electrons in deeper levels; however, the Al-containing persistent phosphors perform better at 80 °C with greater thermal energy. At 20 °C, the trapped electrons in the Al-containing phosphors can be efficiently released with the assistance of additional NIR photostimulation. NIR photostimulated red persistent luminescence (NIR-to-red mode) as presented in the Al-containing ZnGa2O4:Cr,Bi phosphors could be a promising technique for new in vivo imaging systems.