Investigation of the Mechanism of Heterovalent Codoping on the Scintillation Properties of GAGG:Ce Crystals

Gd3(Al,Ga)5O12:Ce (GAGG:Ce) crystal is considered as one of the most efficient scintillators for nuclear medicine imaging devices and γ detection applications due to its high light yield (58,000 ph./MeV), excellent energy resolution (4.9%@662 keV), and high density (6.63 g/cm3). With the introduction of time-of-flight techniques, scintillators are required to have a faster scintillation decay time and higher light yield. An efficient strategy for accelerating the scintillation decay process of GAGG:Ce is mainly through the codoping of low valence ions such as Ca2+. However, the mechanism of codoping has not yet been elucidated, and there is no reasonable explanation for the phenomenon of insignificant improvement in scintillation performance after codoping with some low-valence ions (e.g., Na+). To further investigate the effect of valence on the scintillation properties, three ions with different valence states (Mg2+, Yb3+, and Hf4+) are selected. The scintillation properties deteriorate after Hf4+ codoping, whereas the scintillation decay process is significantly accelerated after Mg2+ and Yb3+ codoping. In addition, the Mg2+ codoped crystal exhibits a low afterglow level. These excellent performances make it very promising for detector applications. Furthermore, the theoretical study of the luminescence mechanism provides a significant reference for the design of high-performance codoped GAGG:Ce crystals.