Synthesis of Small-Sized Mn2+-Doped CsPb(Cl/Br)3 Nanocrystals: Morphology Modulation and Self-Assembly

Mn 2+ -doped perovskite nanocrystals (NCs) have attracted extensive research interest and have been synthesized with sizes in the strong confinement regime. Nevertheless, the size of the doped NCs is still not as small as that of undoped perovskite NCs. To address this, we develop a ligand-assisted reprecipitation method incorporating ultrasonication to synthesize Mn 2+ -doped CsPb(Cl/Br) 3 NCs. The obtained spherical NCs have an average size of 3.1 nm and exhibit orange photoluminescence originating from the 4 T 1 to 6 A 1 transition of Mn 2+ . The luminescent properties correlate with the volume ratio of MnCl 2 to PbBr 2 precursors. Increasing the ratio enhances the Mn 2+ -related emission, while excessive doping leads to photoluminescence quenching. When the precursor ratio is reduced to 1:1, the NCs exhibit both intrinsic exciton and Mn 2+ -related emission, with some particles adopting cubic or rod-like morphologies. Prolonged ultrasonic treatment does not significantly shift the emission peak of the NCs, but promotes superlattice assembly in small-sized NCs, showing a center-to-center separation of 4.2 nm. Subsequently, altering the precursor addition sequence to introduce MnCl 2 last during ultrasonic preparation yields simultaneous formation of spherical and cubic NCs. Finally, post-synthesis doping of Mn 2+ is achieved. Formation of small spherical NCs confirms hypothesis that MnCl 2 induces morphological transformation of NCs. Graphical Ultrasonication-assisted ligand-assisted reprecipitation delivers 3.1 nm Mn 2+ -doped CsPb(Cl/Br) 3 nanocrystals with orange emission from the Mn 2+ 4 T 1 → 6 A 1 transition.