Oleic Acid‐Assisted Nucleation Growth of Highly Luminescent CsCu₂I₃ Single Crystals and Their Films for Flexible and Dynamic High‐Resolution X‐Ray Imaging

Abstract Metal‐halide perovskites have emerged as one of the most promising contenders for the next‐generation X‐ray scintillators on account of their large absorption coefficients, high light yields, and low‐cost fabrication. However, the existing X‐ray scintillators are plagued either by poor stability or high toxicity. Here, highly stable and flexible CsCu₂I₃@polymethyl methacrylate (PMMA) composite films are fabricated simply by a facile one‐step drop‐coating technique. Benefiting from the reasonable light yields (24 100 photons MeV⁻¹), short photoluminescence decay time (207 ns), and flat surface, a low detection limit of 39 nGy_air s⁻¹ and a record‐high resolution of up to 25 lp mm⁻¹ are demonstrated in these CsCu₂I₃@PMMA composite films. The X‐ray imaging tests show that the CsCu₂I₃@PMMA composite films display excellent properties in the dynamic and irregular objects imaging. In addition, the CsCu₂I₃@PMMA composite films exhibit a desirable endurance to the high‐energy X‐ray's irradiation and the water erosion (photoluminescence quantum yield remains up of 90% of its initial value even after submersion in water for 300 h). This work provides a potential to develop eco‐friendly and highly stable halide perovskite materials for high‐resolution X‐ray imaging.