Aliovalent Fe-Substitution-Induced Lattice Reconstruction in CsCu2I3 for Single Crystals High-Performance Color X-ray Imaging

Abstract Metal halide CsCu2I3 (CCI) scintillators are promising candidates for X-ray detection due to their lead-free nature and large Stokes shift, which provides substantial spectral separation between excitation and emission and is favorable for reducing reabsorption. However, their practical applications are constrained by relatively low photoluminescence quantum yield (PLQY) and subsequently insufficient X-ray-to-light conversion efficiency. Herein, we present an aliovalent Fe-substitution strategy to reconstruct the local lattice environment of CCI by partially replacing Cu sites with Fe ions. Density functional theory (DFT) calculations reveal that hybridization of Fe 3d orbitals with the I 5p orbitals in the host lattice alters the electronic states at the valence band edge. The synergistic effects of orbital hybridization, ionic radius mismatch and charge compensation induce a beneficial structural distortion of [CuI4] units, which enhances the carrier capture capabilities of the host. Furthermore, local symmetry breaking optimizes the electron–phonon coupling strength and promotes electron localization, thereby effectively suppressing nonradiative recombination and yielding a remarkable PLQY of 55% and a high light yield of 34,800 photons MeV–1 in CCI-Fe. Finally, the as-grown crystals were triturated and processed into CCI-Fe/PDMS composite scintillation films, which realize a superior X-ray imaging performance with a spatial resolution of 16 lp mm–1. This work provides new insights into designing high-performance lead-free scintillators for X-ray imaging.