Bi3+/Mn2+ Codoping Regulates Chloride Vacancies and Self-Trapped Excitons in Cs2ZrCl6 Scintillators

Lead-free zirconium-based halide scintillators are promising for X-ray detection and imaging owing to their structural stability, defect tolerance, and solution processability. Aliovalent doping can regulate the excited states of vacancy-ordered halide scintillators, but may also generate charge-compensating defects that promote nonradiative recombination. Here, Bi3+/Mn2+ codoping is used to control the defect and excitonic states of vacancy-ordered Cs2ZrCl6. Bi3+ substitution induces local lattice distortion and introduces Bi3+-associated excitation and radiative-decay pathways, while simultaneously increasing the tendency for chloride-vacancy formation. Temperature-dependent photoluminescence, Raman spectroscopy, and thermoluminescence measurements show that Mn2+ redistributes the trap population, suppresses deep-trap-mediated losses, and stabilizes lattice-coupled self-trapped excitons. Density functional theory calculations support an interstitial Mn2+-based charge-compensation configuration that reduces the thermodynamic tendency for chloride-vacancy formation in the Bi3+-doped lattice. Consequently, the photoluminescence quantum yield increases from 34.8% to 84.12%, and the optimized scintillator exhibits a light yield of 56,840 photons MeV-1, a detection limit of 2.84 μGy s-1, and stable radioluminescence under continuous irradiation. A multilayer flexible screen further achieves a spatial resolution of 30 lp mm-1 and enables curved-surface and underwater X-ray imaging. These results demonstrate how coupled aliovalent substitution and charge compensation regulate defect formation and self-trapped-exciton recombination in Cs2ZrCl6 scintillators.