Research of Efficient and Fast Scintillator Garnet Crystals: The Role of Ce⁴⁺ in Ce³⁺, Mg²⁺-Co-Doped Gd₃Al₂Ga₃O₁₂ from Spectroscopic and XANES Characterizations

Abstract

In this lecture, two main goals have been shown: first, the state-of-art of the inorganic scintillator materials used for many important applications and, secondly, the illustration of the dynamics of this field by giving spectroscopic and scintillation properties of the most advanced oxide scintillator Ce³⁺, Mg²⁺-co-doped Gd₃Al₂Ga₃O₁₂ (GAGG) garnet host, grown by using both the micro-pulling-down (μ-PD) and the Czochralski methods at the Tohoku University, Sendai. The adopted strategy for optimization of garnet scintillator composition in both, the defect engineering and band gap engineering of this research program gives us the opportunity to discuss on the role of Ce⁴⁺ ion which has always been a challenge for Ce³⁺-doped luminescent crystals. By analogy with the approach used for commercial Ce³⁺, Mg²⁺-co-doped-doped orthosilicates as Lu₂SiO₅ (LSO) and (Lu_1−xY_x)₂SiO₅ (LYSO), we confirm the creation of stable Ce⁴⁺ oxidation state and we evaluate the Ce³⁺/Ce⁴⁺ ratio of concentrations in Ce³⁺, Mg²⁺-co-doped Gd₃Al₂Ga₃O₁₂ (GAGG) garnet by XANES spectroscopy analysed at the Ce L_III threshold of the European Synchrotron Radiation Facility (ESRF) in Grenoble.