Programming a Trap‐State Landscape via Compositional Gradients for Superior X‐ray Storage Perovskite Imagers

ABSTRACT Halide perovskite X‐ray detectors have reached impressive sensitivities, but their charge‐trapping behavior remains a serendipitous property rather than a designed one. We introduce compositional gradient engineering as a paradigm to actively program the trap‐state landscape. In Sb 3+ ‐doped Cs 2 NaSc 1‐x Lu x Cl 6 perovskites, we leverage Sc/Lu gradients to induce tailored lattice disorder, enabling predictive control over both trap density and depth. This is visualized by a fully tunable thermoluminescence spectrum from 100 to 550 K, a signature of programmable trap energies distinct from systems like Cs 2 Sn 1‐x Zr x Cl 6 tuned solely for bandgap shifting. The Sb 3+ activator, with its unique ns 2 configuration, is integral to this design, functioning as a co‐engineered, dual‐functional trap modulator that provides both deep electron and deep hole traps. The optimized phosphor's charge storage capacity surpasses the commercial benchmark BaFBr(I):Eu 2+ by 4.5 times, enabling an ultra‐low detection limit of ∼99 nGy air /s and excellent stability (87% signal retention after one hour). This work establishes a rational design principle for functional trap‐state programming, moving beyond serendipitous discovery to the intentional engineering of storage properties in halide perovskites for advanced, temperature‐resilient radiography.