Mutual Interactions between Emission Centers in Colloidal Sb3+/Mn2+-Codoped Cs2CdCl4 Ruddlesden–Popper Phase Nanocrystals

Abstract

Low-dimensional cadmium-based halide perovskites are a promising platform for tunable luminescent materials because of their structural diversity, high dopant tolerance, and strong exciton localization. A simple solution-phase reaction produces a variety of unique bulk phases, including all-inorganic Ruddlesden–Popper layered structures, such as Cs2CdCl4 and Cs3Cd2Cl7, and allows for incorporation of different dopant centers. Here, we demonstrate the synthesis of Sb3+/Mn2+-codoped Cs2CdCl4 colloidal nanocrystals and investigate in detail their optical properties arising from the mutual interactions between dopant ions. In codoped nanocrystals, Sb3+ introduces a broad green luminescence, which is attributed to self-trapped exciton recombination, while Mn2+ produces orange-red delayed emission, corresponding to the intraionic 4T1 → 6A1 transition. Our results indicate the coexistence of highly efficient energy transfer from Sb3+-related self-trapped exciton and much less efficient energy transfer from the host lattice excited states to Mn2+ emission centers. We further demonstrate that both Sb3+ and Mn2+ have multiple roles in generating the emission of codoped Cs2CdCl4 nanocrystals, mediated by strong local lattice relaxation and exciton–phonon coupling. The Sb3+ dopants act as luminescence activators and sensitizers of the Mn2+ emission, while Mn2+ dopants act as secondary emission centers and provide thermal stabilization of Sb3+-related self-trapped exciton. The results of this work offer additional insight into complex photophysical processes in colloidal cadmium halide nanomaterials, which show significant promise in lighting, display, anticounterfeiting, and optical information encryption.