Mechanochromism-Free Cu4I4 Complex-Based Scintillators for Highly-Efficient X-Ray Excited Luminescence and Highly-Resolution X-Ray Tomography Imaging

Copper(I) halide cluster-based complexes (especially Cu₄X₄) are promising scintillators, but their practical application is limited by mechanochromism and nonradiative decay from cluster-centered (3CC) transitions. Herein, novel octahedral or distorted-octahedral Cu₄X₄ (X = Cl, Br, I) clusters are reported, stabilized by a rigid diphenyl-2-pyridylphosphine ligand. These structures differ from classical cubane or stairstep geometries. The rigid ligand and intermolecular π–π interactions (π_Ph–π_Ph or π_Py–π_Ph) effectively suppress ³CC-induced distortions and promote radiative ³(M+X)LCT emission. A small singlet–triplet energy gap (ΔE_ST) enables dual emission pathways via thermally activated delayed fluorescence (TADF) and phosphorescence, leading to shortened lifetimes, high quantum yields (PLQY up to 87.77%), and a steady-state X-ray relative light yield 2.5-fold higher than commercial scintillator Bi₄Ge₃O₁₂. The corresponding flexible scintillator films exhibit excellent spatial resolution (>20 lp mm⁻¹), and enable accurate 3D reconstruction of complex industrial components. These results highlight a robust strategy to enhance luminescence efficiency and stability of Cu₄X₄-based scintillators, offering great potential for high-resolution panoramic X-ray imaging and X-ray tomography in medical diagnosis and industrial non-destructive inspection.