Dexter Energy Transfer in Zero-Dimensional Inorganic Metal Halides for Obtaining Near-Unity PLQY via Sb3+/Mn2+ Codoping

Multi-ion codoping strategies have been intensively studied for metal halide perovskite optical engineering. Although tunable dual broadband emissions can be achieved by pairing Sb3+/Mn2+ doping centers in metal halide hosts, there have been few reports of highly efficient light emission with a near-unity photoluminescence quantum yield (PLQY). In this study, Mn2+ dopants are incorporated into a Sb3+-doped Rb4CdCl6 system. Tunable dual emissions and a substantial increase in the PLQY from ∼60% to near-unity (98%) are achieved. Energy transfer is strong and localized and occurs only between the Sb3+ donor and the adjacent Mn2+ acceptor. The green self-trapped exciton emission (524 nm) is converted into a red d–d emission (607 nm) without changing the excitation profile. The Sb3+ optical centers without adjacent Mn2+ species maintained their original green emission. Spectroscopic and probabilistic investigations showed that the luminescent and thermally quenched Sb3+ optical centers play identical roles in the energy-transfer process, and nonradiative recombination was successfully inhibited. These findings clarify how Sb3+ and Mn2+ dopants couple in the metal halide host and facilitate the design of high-performance materials that give tunable broadband fluorescence via an energy-transfer process.