High performance X-ray imaging enabled by a localized lattice modulated Cs₃Cu₂Br₅ scintillator

Zero-dimensional lead-free all-inorganic halides Cs₃Cu₂X₅ (X = Cl, Br and I) effectively confine excitons within their isolated [Cu₂X₅]³⁻ polyhedral units, thereby generating strong quantum confinement effects that lead to superior performance in X-ray detection applications. However, due to the strong electron–phonon coupling strength, large bandgap, and numerous defects, Cs₃Cu₂Br₅ nanocrystals suffer from severe nonradiative recombination and low photoluminescence quantum yield (PLQY). Herein, we propose a localized lattice modulation strategy, thereby effectively improving the optical performance while maintaining an ultrafast luminescence decay (∼2 ns). The precise concentration control of Na⁺ dopants with a smaller ionic radius enables substitution induced lattice contraction rather than interstitial site doping induced lattice expansion, thus forming denser Cu–Br polyhedra. The alteration of the localized lattice structure significantly reduces the electron–phonon coupling strength and non-radiative losses, resulting in a 2.3-fold increase in emission intensity. When integrating the optimized nanocrystals into a flexible PMMA composite film for X-ray imaging, a high light yield of 22 530 photons per MeV with a pretty low X-ray detection limit (2.19 µGy_air s⁻¹) and a high spatial resolution of 24.3 lp mm⁻¹ can be achieved. Moreover, the radiation hardness of the scintillator is significantly improved, which can be attributed to the lattice contraction caused by Na⁺ doping. This work highlights the critical role of localized crystal structure modulation in enhancing self-trapped exciton (STE) emission performance and demonstrates great potential for high-resolution X-ray imaging applications.