Efficient Rare‐Earth‐Based Hybrid Metal Halide Single‐Crystal Scintillators Enabled by Antimony‐Assisted Triplet Exciton‐Harvesting

. By optimizing Sb concentration, we achieved a 2.06-fold increase in RL intensity for Tb-based systems and a 1.33-fold enhancement for Eu-based systems. The resulting scintillators exhibit a high light yield of 19022 photons/MeV, ultralow detection limits of 124 nGy/s, and robust radiation resistance. Centimeter-scale single crystals grown for x-ray imaging demonstrated a high spatial resolution of 15.7 lp/mm. Moreover, color-tunable radioluminescence realized by adjusting the Tb/Eu ratio highlights their potential for color-visualized radiation detection.