Ultrafast Study of Exciton Transfer in Sb(III)-Doped Two-Dimensional [NH₃(CH₂)₄NH₃]CdBr₄ Perovskite

Antimony-based metal halide hybrids have attracted enormous attention due to the stereoactive 5s² electron pair that drives intense triplet broadband emission. However, energy/charge transfer has been rarely achieved for Sb³⁺-doped materials. Herein, Sb³⁺ ions are homogeneously doped into 2D [NH₃(CH₂)₄NH₃]CdBr₄ perovskite (Cd-PVK) using a wet-chemical method. Compared to the weak singlet exciton emission of Cd-PVK at 380 nm, 0.01% Sb³⁺-doped Cd-PVK exhibits intense triplet emission located at 640 nm with a near-unity quantum yield. Further increasing the doping concentration of Sb³⁺ completely quenches singlet exciton emission of Cd-PVK, concurrently with enhanced Sb³⁺ triplet emission. Delayed luminescence and femtosecond-transient absorption studies suggest that Sb³⁺ emission originates from exciton transfer (ET) from Cd-PVK host to Sb³⁺ dopant, while such ET cannot occur with Pb²⁺-doped Cd-PVK because of the mismatch of energy levels. In addition, density function theory calculations indicate that the introduced Sb³⁺ likely replace the Cd²⁺ ions along with the deprotonation of butanediammonium for charge balance, instead of generating Cd²⁺ vacancies. This work provides a deeper understanding of the ET of Sb³⁺-doped Cd-PVK and suggests an effective strategy to achieve efficient triplet Sb³⁺ emission beyond 0D Cl-based hybrids.