Zero-dimensional (OD) inorganic perovskites have recently emerged as a new class of material for optoelectronics owing to their outstanding excitonic properties, strong photoluminescence (PL), and high exciton binding energy. These materials have a unique quantum-confined structure, which originates from the presence of fully isolated octahedra exhibiting single-molecule behavior. In this work, we probed the optical behavior of single molecule-like isolated octahedra in OD Cs4PbX6 (X = Cl, Br/Cl) perovskite through isovalent (Mn~(2+)) doping at Pb sites. The incorporation of Mn~(2+) stabilizes the Cs4PbX6 phase by lowering the symmetry of PbX6 via enhanced octahedral distortion (preventing the high-symmetry cubic CsPbX3 impurity) and controlling the compositional variation of Cs-Pb salts. This strategy enabled the synthesis of CsPbX3 free Cs4PbX6 nanocrystals. A high PL quantum yield (QY) of Mn~(2+) emission was obtained in the colloidal (29%) and solid (21%, powder) forms. These performances can be attributed to structure-induced confinement effects, which enhance the energy transfer from localized host exciton states to Mn~(2+) dopant within the isolated octahedra of OD perovskite. The present findings could lead to designing of low-dimensional perovskites as efficient light emitters with photo and chemical stability for high-performance optoelectronic devices.
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