Yttrium Oxide-Deficient Melts Control Secondary-Phase Distribution in Cerium-Doped Terbium–Yttrium Aluminum Garnet Crystals for White-Light Conversion and X-ray Imaging

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Controlled melt nonstoichiometry was investigated as a processing parameter governing secondary-phase formation and functional properties of Ce3+-doped (Tb,Y)3Al5O12 single crystals grown by micropulling-down. Crystals were grown from melts with 0, 3, 6, 9, and 11 mol % Y2O3 deficiency. X-ray diffraction, electron probe microanalysis, and Raman spectroscopy revealed phase-pure garnet up to 3 mol % deficiency, rim-localized α-Al2O3 inclusions at 6 and 9 mol %, and core-localized perovskite-type inclusions at 11 mol %. Secondary-phase formation modified Tb/Y partitioning in the garnet matrix, affecting Ce3+ emission kinetics, Tb3+↔Ce3+ energy transfer, trap depth, and scintillation properties. The 11 mol % deficient crystal showed the highest thermal stability, with the Ce3+ thermal-quenching onset shifting from 375 to 425 K. The 9 mol % deficient crystal reached a luminous efficacy of 158 lm/W and a scintillation light yield of 33,600 photons/MeV. X-ray radiography using the 9 mol % Y2O3-deficient crystal showed clear images of an SD card. These results indicate that melt nonstoichiometry can tune the balance between photoconversion and scintillation performance in rare-earth garnets.