A Hybrid Manganese Halide Scintillator with a High X-ray Absorption Coefficient for X-ray Imaging

Manganese-based hybrid metal halides are attractive for scintillator applications due to their high emission efficiency and good stability. However, most high-performance manganese scintillators rely on bulky and complex organic cations as A-site components, which reduce the lattice density and compromise X-ray absorption. To address this issue, we employed a small piperidinium cation (C₅H₁₂N⁺) to synthesize a zero-dimensional manganese halide, (C₅H₁₂N)₂MnBr₄, via solvent evaporation. This material shows green Mn²⁺ emission but suffers from concentration quenching, giving a low PLQY of 23.86%. Through Cd²⁺ alloying, the optimized (C₅H₁₂N)₂MnBr₄: 20%Cd achieves a markedly enhanced PLQY of 78.54%. As a scintillator, it exhibits excellent X-ray absorption─among the highest reported for hybrid manganese scintillators─and a high light yield of 21086 photons/MeV. This improvement results from the synergy between the small A-site cation (providing a compact lattice for strong absorption) and Cd²⁺ alloying (suppressing concentration quenching). A 10 × 10 cm flexible film fabricated by incorporating the alloyed powder into a TPU matrix shows outstanding radiation stability and a high X-ray imaging resolution of 14 lp mm^-1. The combination of strong X-ray absorption, enhanced luminescence, and solution processability opens new opportunities for low-cost, large-area, flexible X-ray detectors and imaging.