In this paper, the most advanced oxide scintillator Ce 3+ , Mg 2+-co-doped Gd 3 Al 2 Ga 3 O 12 (GAGG) garnet host, grown by using the Czochralski method at the Tohoku University, Sendai, is reported. The charge transfer absorption band in UV, like in other Ce 3+ , Mg 2+-codoped oxides, reveals the creation of stable Ce 4+ oxidation state, in addition of the usual Ce 3+ one, admitted as responsible of the scintillation mechanism improvement displayed by this garnet. Strangely, the confirmation of quantitative values of Ce 4+ concentration has never been done and the goal is mainly focused on the presence of Ce 4+ and the evaluation of the Ce 3+ /Ce 4+ ratio measured by XANES spectroscopy at the Ce L III threshold of the European