Controlling Ce3+ 5d states dynamics in zinc-based metal halide scintillator via hot exciton manipulation

The Ce ³⁺ -doped metal halides are recognized as ultrafast scintillators due to their allowed 5d→4f radiative transitions, which enable fast decay and high light yield. However, in certain hosts such as Cs ₂ ZnCl ₄ , Ce ³⁺ emission is limited by inefficient energy transfer and competitive self-trapped exciton (STE) recombination. Here, we grow a series of centimeter-scale, high-quality Ce ³⁺ -doped and Ce ³⁺ –Cu ⁺ co-doped Cs ₂ ZnCl ₄ single crystals with tunable dopant concentrations, and elucidate their carrier relaxation pathways using transient absorption spectroscopy across fs–µs timescales. This Ce ³⁺ –Cu ⁺ co-doping strategy modulates the Ce ³⁺ 5d energy landscape and facilitates the participation of STEs in radiative recombination. Specifically, co-doping deepens the lowest 5d potential well and promotes Ce ³⁺ →STE energy transfer. It also redistributes exciton populations between localized and delocalized 5d states and facilitates faster carrier relaxation. As a result, the X-ray excited luminescence intensity is enhanced by nearly an order of magnitude, while the fast γ-ray scintillation decay component is shortened from 4.3 to 2.4 ns. These findings establish a direct link between Ce ³⁺ 5d dynamics, hot-exciton redistribution, and dopant–host coupling, providing a rational strategy for designing high-efficiency ultrafast scintillators.