Low‐Melting and Configuration‐Tunable Copper Halide Scintillators via Steric Hindrance Optimization for Large‐Area Single‐Crystal X‐Ray Imaging

ABSTRACT Achieving simultaneous control over thermal processability, structural configuration, and crystal growth remains a formidable challenge in scintillator development. Herein, we introduce a “one stone, three birds” design paradigm based on steric hindrance engineering that synergistically regulates melting behavior, cluster architecture, and crystal growth in copper‐based halide scintillators. Mechanistic studies reveal that enhanced steric hindrance first weakens ligand‐cluster electrostatic interactions, leading to a reduced melting temperature, then reduces local Cu/Br concentration which diversifies cluster configurations with tunable emission, and further improves solubility for large‐area crystal growth. Ab initio molecular dynamics simulations confirm the increased atomic motion and liquid‐like dynamic disorder in the high‐steric‐hindrance compound (TBA)CuBr 2 (Tetrabutylammonium = TBA). The resulting materials exhibit excellent melt processability with the lowest melting point of 50°C and the highest PLQY of 99%, representing a 6‐fold enhancement over (TBA) 2 Cu 4 Br 6 , with an excellent X‐ray light output of 382%LYSO. Benefiting from improved solubility, we successfully grew large‐area (∽2 cm × 4 cm) single‐crystalline films that deliver a spatial resolution of 28 lp mm −1 , 3.4 times higher than that of polycrystalline films. Remarkably, this strategy is broadly applicable to Mn − and Sb − based hybrid halides. Overall, this work establishes a general steric‐control design principle toward low‐melting, structurally tunable, and solution‐processable high‐performance scintillators.