Effect of dopant concentration on the optical characteristics of Cr3+:ZnGa2O4 transparent ceramics exhibiting persistent luminescence

ZnGa 2 O 4 (ZGO) persistent luminescence (PersL) ceramics doped with different concentrations of Cr 3+ were prepared by the co-precipitation method and hot isostatic pressing (HIP) post-treatment. After HIP post-treatment, the ZGO PersL ceramics was significantly improved from opaque to transparent visual appearance due to the elimination of micro-pores during HIP process. The effects of Cr 3+ concentration on the morphology, transmittance and PersL properties of ZGO PersL ceramics were systematically investigated. The ZGO PersL ceramics with higher Cr 3+ dopant concentrations show less micro-pores and higher transmittance, which indicates that the Cr 3+ can also work as a sintering additive to increase the density and to improve the optical quality of ZGO PersL ceramics. The photoluminescence excitation (PLE) and emission (PL) intensities increase with the increase of Cr 3+ concentration up to 0.25 at.%. At yet higher Cr 3+ concentrations, the ZGO PersL ceramics exhibits weaker PL and PLE intensities which is probably caused by the concentration quenching effect. However, the PersL decay curves show that the PersL performance of ZGO ceramics increases with increasing Cr 3+ concentrations, indicating that the doping by Cr 3+ ions may cause another traps formation leading to stronger and longer PersL. The PersL decay curves of all ZGO PersL ceramics were fitted by the second-order exponential function, indicating that at least two kinds of traps with different electron release rates exist in the ZGO ceramics. The influence of Cr 3+ concentration on the thermoluminescence (TL) of ZGO PersL ceramics was also studied, and the results showed that the TL curves of the pre-sintered ceramics shifted to lower temperatures, indicating that the depth of trap related to Cr 3+ ions is shallower than the depth of trap caused by the intrinsic defects.