Efficient Mn²⁺ Doping in Non-Stoichiometric Cesium Lead Bromide Perovskite Quantum Dots

Doping magnetic transition metal ions (e.g., Mn²⁺) into colloidal quantum dots endows novel optical and magnetic properties to the host materials. CsPbBr₃ quantum dots (QDs) are emerging light-emitting materials with high structural and chemical flexibility in the visible spectral regime. However, efficiently doping Mn²⁺ ions in CsPbBr₃ QDs remains challenging, especially when size confinement is needed for strong exciton-dopant exchange interaction. Here, we introduce a new category of CsPbBr₃ QDs that are severely Cs-deficient, enabling facile Mn²⁺ doping in strongly confined CsPbBr₃ QDs with near unity Mn²⁺ photoluminescent efficiency. Due to the non-stoichiometry-induced surface charging, Mn²⁺ cations can be tightly adsorbed on QDs, facilitating their incorporation and suppressing the fast QD self-purification. Our non-stoichiometric synthesis can constantly achieve a Mn²⁺ doping concentration of >15% with >90% Mn²⁺ photoluminescence efficiency, which is robust against purification with non-solvents and long-term storage. We additionally determined the intrinsic exciton-to-Mn energy transfer rate in the CsPbBr₃ QD lattices, which was difficult due to inefficient Mn²⁺ doping and structural uncertainty in CsPbBr₃ nanocrystals. Our novel doping strategy should prove applicable to a variety of dopants in previously “almost undopable” lead bromide perovskite QDs, which will greatly expand the optical and magnetic properties of this modern material for high-efficiency solar concentrators, light-emitting diodes, and new magneto-optical devices.