Host–Dopant Engineering of Ce 4+ ‐Dominant Y 3 (Al,Ga) 5 O 12 :Ce,Mg Scintillators for High‐Performance X‐Ray Imaging

Fast scintillators are essential for advanced X‐ray imaging and time‐of‐flight techniques. Although stabilizing Ce 4+ ions in garnet hosts is an effective strategy for suppressing the afterglow and accelerating scintillation, it often introduces quenching pathways that reduce the light yield. This study demonstrates that synergistic host‐dopant engineering in Mg 2+ co‐doped Y 3 (Al,Ga) 5 O 12 :Ce enables controlled Ce 4+ ‐ion stabilization and reveals a strong Ga‐dependent efficiency of Ce 3+ to Ce 4+ conversion. The X‐ray absorption near edge structure spectroscopy results indicate Ce 4+ fractions of 64% and 25% in Y 3 Al 3 Ga 2 O 12 :Ce,Mg and Y 3 Al 2 Ga 3 O 12 :Ce,Mg, respectively. Moreover, vacuum–UV spectroscopy demonstrates that Ce 4+ ions strongly suppress trap‐mediated energy transfer to the Ce 3+ fraction, indicating a redistribution of carrier capture away from defect‐related pathways. This valence state control yields an accelerated scintillation response (30–50 ns), representing a 7.1‐ and 3.6‐fold increase in light yield for Y 3 Al 3 Ga 2 O 12 and Y 3 Al 2 Ga 3 O 12 respectively, and > 10 2 reduction in the afterglow. The X‐ray imaging of biological specimens and electronic components demonstrates an improvement in spatial resolution relative to a standard Lu 3 Al 5 O 12 :Ce scintillator. These results establish Ce charge‐state engineering as a composition‐sensitive design principle for achieving superior garnet scintillators with both fast response and high light output.