Defect‐Mediated Scintillation in Fully Inorganic Perovskites via Water‐Induced 0D/3D Phase Modulation

Scintillation detectors are essential tools in high‐energy physics, medical imaging, and security, due their efficiency in converting ionizing radiation into visible light. Lead‐based inorganic perovskites, particularly 3D CsPbBr 3 , have emerged as promising next‐generation scintillators due to their high photon attenuation and fast emission properties. In contrast, the 0D phase, Cs 4 PbBr 6 , exhibits unique emission characteristics and defect‐mediated behavior, offering additional opportunities to tune scintillation performance in hybrid systems. However, the role of the 0D Cs 4 PbBr 6 phase in scintillation has remained largely unexplored, and the mechanism of the emission is not well understood. Herein, a simple and reproducible synthesis of polycrystalline perovskite powders is developed with the specific scope of modulating the 3D/0D CsPbBr 3 /Cs 4 PbBr 6 phases in the samples, aiming to clarify the role of the 0D phase in the emission properties of the materials. The method relies on a solvent‐antisolvent approach, in which incremental water additions selectively promote the formation of the 3D phase over the 0D one. The scintillation properties of the resulting powders are evaluated, revealing an increased scintillation yield for low water volumes used in the synthesis and an ultrafast decay time under X‐ray radiation. Cathodoluminescence and temperature‐dependent radioluminescence highlight defect‐driven scintillation mechanisms, providing insights for future material optimization.