Dissimilar behavior of YAG:Ce and LuAG:Ce scintillator garnets regarding Li+ co-doping

Using a combination of experimental methods, the substitution tendencies of Li+ and involved charge compensation mechanisms are determined and compared in two important similar scintillators, LuAG:Ce and YAG:Ce. The studies were performed on polycrystalline samples prepared by solid phase reactions as well as in single crystals grown by the vertical Bridgman method. The results show that Li+ in LuAG:Ce, Li is localized mainly at Lu3+ sites with charge compensation brought about by Ce3+ Ce4+ conversion and creation of anion vacancies. Surprisingly, unlike LuAG:Ce, Li, no evidence for Li+ substitution at Y3+ sites and conversion of Ce3+ to Ce4+ has been obtained in YAG:Ce, Li. It suggests that Li+ goes mainly to interstitial positions and does not interact with Ce3+. From an application point of view, Li+ co-doping of YAG:Ce is not efficient to improve the scintillationdecay parameters, however, it is efficient to reduce the amount of anion vacancies in both YAG and YAG:Ce.