Synchronous lifetime elongation and electron–phonon coupling reveal cascade sensitization in Sb-doped Cs4PbCl6 perovskite nanocrystals

Zero-dimensional metal halide perovskites with strong self-trapped exciton (STE) emission are promising for efficient lighting and sensing, but STE → dopant energy transfer is not well quantified. Here we use Sb 3+ -doped Cs 4 PbCl 6 nanocrystals as a model and combine temperature-dependent steady-state and time-resolved photoluminescence, rate-equation analysis and first-principles calculations to clarify the STE → Sb 3+ cascade sensitization. Emission and excitation spectra confirm successful Sb incorporation. The 360 nm ultraviolet band is assigned to STE recombination, whereas the green band originates from STE → Sb 3+ transfer and the Sb 3+ 3 P 1 → 1 S 0 transition. The transfer efficiency (∼64 %) shows that STE feeding dominates the excitation of Sb centers. Low-temperature PL analysis reveals distinct electron–phonon coupling: STE emission couples mainly to low-frequency phonons, while Sb 3+ emission couples more strongly to high-frequency modes. The extracted activation energies and the cooperative increase of τ STE and τ Sb with decreasing temperature support a thermodynamically downhill STE → Sb 3+ migration. Within a rate-equation framework, the rise time of Sb 3+ emission satisfies t rise ≈ τ STE and yields a characteristic cascade-like transient profile. Density-functional calculations indicate Sb-5p acceptor levels inside the bandgap, providing an energetic basis for localized STE → Sb 3+ coupling and design guidelines for efficient 0D perovskite emitters.