Ultrasmall CsPbBr₃ Blue Emissive Perovskite Quantum Dots Using K-Alloyed Cs₄PbBr₆ Nanocrystals as Precursors

We report a colloidal synthesis of blue emissive, stable cube-shaped CsPbBr₃ quantum dots (QDs) in the strong quantum confinement regime via dissolution-recrystallization starting from pre-syntesized (K Cs_1- )₄PbBr₆ nanocrystals which are then reacted with PbBr₂. This is markedly different from the known case of Cs₄PbBr₆ nanocrystals that react within seconds with PbBr₂ and get transformed into much larger, green emitting CsPbBr₃ nanocrystals. Here, instead, the conversion of (K Cs_1- )₄PbBr₆ nanocrystals to CsPbBr₃ QDs occurs in a time span of hours, and tuning of the QD size is achieved by adjusting the concentration of the precursors. The QDs exhibit excitonic features in optical absorption that are tunable in the 420-452 nm range, accompanied by blue photoluminescence with quantum yield around 60%. Detailed spectroscopic investigations in both the single and multiexciton regime reveal the exciton fine structure and the effect of Auger recombination of these CsPbBr₃ QDs, confirming theoretical predictions for this system.