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 and ensemble uniformity are needed for understanding the underexplored exciton-dopant exchange interaction. Here, we introduce a doping mechanism based on electrostatic surface Mn²⁺ adsorption that enables efficient Mn²⁺ incorporation in strongly confined CsPbBr₃ QDs. The resultant QDs are found to have a Cs-deficient stoichiometry compared to their undoped counterparts. A redox reaction-based purification method was developed to remove Mn²⁺ cations that are tightly adsorbed on the surface to determine the concentration of lattice-incorporated Mn²⁺. Our synthesis enables a Mn²⁺ doping/alloying concentration of up to ∼44% with a Mn²⁺ photoluminescence efficiency exceeding 90%. This allows for the determination of the intrinsic exciton-to-dopant energy transfer rate.