Potassium-regulated lead-free cesium copper iodide Cs3Cu2I5 perovskites with enhanced scintillation properties and their application in high-resolution X-ray imaging

Abstract

Ternary copper halides, such as Cs₃Cu₂I₅, as an emerging class of nontoxic alternatives to lead halide perovskites, have drawn extensive attention in the X-ray detection field due to their efficient self-trapped exciton emissions. However, the light yield far below the theoretical limit seriously hinders the high-resolution X-ray detection application of copper halide scintillators. Herein, Cs₃Cu₂I₅:K⁺ scintillation films and single crystals with enhanced photoluminescence (PL) and radiation luminescence (RL) were first obtained by adjusting the doping concentration of K⁺ ions in the 0–8 at% range. The substitution of Cs⁺ by doping K⁺ compacted the adjacent [Cu₂I₅]³⁻ dimer groups, resulting in a stronger exciton–photon coupling strength. Therefore, Cs₃Cu₂I₅:K⁺ single crystals exhibited a stronger RL emission under X-ray excitation, and their light output was about 49.6% higher than that of the pure Cs₃Cu₂I₅, with an accelerated scintillation decay time (330 to 241 ns). Benefiting from these advantages, X-ray detectors based on hydrophobic polymethyl methacrylate (PMMA)-coated Cs₃Cu₂I₅:K⁺ flexible films could deliver a higher X-ray imaging resolution of 11.7 lp mm⁻¹@MTF = 0.2 in comparison with the commercial gadolinium oxysulfide (GOS)-based detectors (6.2 lp mm⁻¹@MTF = 0.2). This work provides insights for the design of metal halides for use in low-cost and high-resolution flexible X-ray imaging systems.