Sang Hyun Nam

Radiation detectors operating in extreme environments such as nuclear accident sites, radioactive waste facilities, space missions, and post‐detonation scenarios must maintain reliable radionuclide identification under prolonged high‐dose irradiation. However, radiation‐induced defect accumulation progressively degrades spectroscopic performance, and the mechanisms governing reversible detector operation under extreme irradiation remain not fully understood. Here, we report a zero‐dimensional perovskite‐inspired Cs ₃ Cu ₂ I ₅ single‐crystal scintillator that exhibits fully reversible spectroscopic degradation under ultra‐high‐dose γ‐ray irradiation of ∼200 kGy. The radiation response was systematically investigated by correlating structural, optical, and spectroscopic analyses before and after mild thermal recovery. Structural and spectroscopic analyses reveal that irradiation induces predominantly interstitial‐type lattice disorder while preserving long‐range crystallinity and the intrinsic self‐trapped exciton emission framework. Despite reduced light output, the degraded spectroscopic performance is completely restored through mild thermal activation at 100°C without device refabrication. Under simultaneous six‐radionuclide γ‐ray fields, the scintillator maintains distinguishable spectral features and high post‐irradiation energy linearity (R ² = 0.9973), outperforming conventional NaI(Tl) under comparable conditions. These findings highlight defect‐mediated reversibility as a promising design strategy for radiation‐resilient scintillators operating in extreme environments.

Chiral Pb-free metal-halide semiconductors (MHSs) have attracted considerable attention in the field of spintronics due to various interesting spin-related properties and chiral-induced spin selectivity (CISS) effect. Despite their excellent chemical and structural tunability, the material scope and crystal structure of Pb-free chiral MHSs exhibiting the CISS effect are still limited; chiral MHSs that have metal-halide structures of octahedra and tetrahedra are only reported. Here, we report a new class of chiral MHSs, of which palladium (Pd)-halides are formed in 1D square-pyramidal structures or 0D square-planar structures, with a general formula of ((R/S-MBA)₂PdBr₄)_1-x((R/S-MBA)₂PdCl₄)_x (MBA = methylbenzylammonium; x = 0, 0.25, 0.5, 0.75, and 1) for the first time. The crystals adopt the 1D helical chain of Pd-halide square-pyramid (for x = 0, 0.25, 0.5, and 0.75) and 0D structure of Pd-halide square-plane (for x = 1). All the Pd-halides are distorted by the interaction between the halide and the chiral organic ammonium and arranged in a noncentrosymmetric position. Circular dichroism (CD) for ((R/S-MBA)₂PdBr₄)_1-x((R/S-MBA)₂PdCl₄)_x indicates that chirality was transferred from chiral organic ammonium to Pd-halide inorganics. ((R-MBA)₂PdBr₄)_1-x((R-MBA)₂PdCl₄)_x (x = 0, 0.25, 0.5, and 0.75) shows a distortion index of 0.127-0.128, which is the highest value among the previously reported chiral MHSs to the best of our knowledge. We also find that (R/S-MBA)₂Pd(Br_1-xCl_x)₄ crystals grow along the out-of-plane direction during spin coating and have high c-axis orientation and crystallinity, and (R/S-MBA)₂Pd(Br_1-xCl_x)₄ (x = 0 and 0.5) crystals exhibit a CISS effect in polycrystalline bulk films. These results demonstrate the possibility of a new metal-halide series with square-planar structures or square-pyramidal structures for future spintronic applications.