Gradient Orbital Coupling in Mn-Doped Asymmetric Units Amplifies Red Emission of NH4CdCl3 for X-Ray Scintillation Imaging

Halide perovskites are promising for applications in light-emitting diodes, multilevel anti-counterfeiting, and radiation detection due to their excellent luminescence properties. Mn 2+ doping can further tailor the optical properties of perovskites, yet its microscopic mechanism remains insufficiently understood. Here, we report a gradient orbital coupling-enhanced red emission with a nearly tenfold increase in photoluminescence quantum yield by doping 0.12% Mn 2 + into 1D NH 4 CdCl 3 perovskite, constructing asymmetric Cd-Cl-Mn functional units. First-principles calculations indicate that orbital hybridization among Cd(5s, 4d), Cl(3p), and Mn(3d) orbitals in these asymmetric Cd-Cl-Mn units creates a stepped carrier-transport pathway via the formation of coupled gradient orbitals. Transition dipole moment analysis and partial charge mapping reveal that electrons transiently occupy the conduction-band-coupled Mn 3d orbitals before relaxing to the conduction band minimum, while most of the holes are localized at Cd sites. This carrier redistribution enhances radiative recombination, thereby optimizing emission efficiency. The as-prepared semitransparent scintillator films incorporating NH 4 CdCl 3 : Mn deliver strong 630 nm emission under x-ray excitation for high-resolution imaging. Our findings demonstrate that gradient orbital coupling serves as an effective strategy for enhancing luminescence, paving the way for high-efficiency perovskite-based optoelectronic materials and devices.