We report our investigation on the transformation pathway from precursor compounds (PCs) to magic-size clusters (MSCs) for semiconductor ZnS. We show, for the first time, a synthetic approach to ZnS MSCs in a single-ensemble form exhibiting optical absorption peaking at 269 nm. We thus symbolize the MSCs as MSC-269. The synthesis was performed with zinc oleate (Zn(OA) 2 ) and elemental sulfur (S) as the respective Zn and S sources and 1-octadecene (ODE) as the reaction medium. Prior to the addition of S, oleylamine (OLA) is mixed with Zn(OA) 2 . ZnS MSC-269 evolved at a relatively high temperature from a reaction mixture or at room temperature during a dispersion incubation of a reaction product in a solvent. Both optical absorption and NMR studies support that the evolution of colloidal semiconductor MSCs contains three different stages. The present study narrows our knowledge gap on PC-to-MSC transformations that involve a loss of ligands from the PC.
All-inorganic cesium lead halide perovskites have received much attention, but the study of the formation pathway is relatively little. We report here a new one-step approach for the synthesis of Cs 4 PbBr 6 nanocrystals (NCs), as well as the exploration of its formation process. Mixing three independent precursors of Cs, Pb, and Br in a cuvette, we monitor the evolution of Cs 4 PbBr 6 NCs by in situ absorption spectroscopy, the formation of which features a sharp absorption peak at 313 nm. Based on this model, we further divide the synthesis process into two stages, in which the two precursors react for a certain period before adding the third precursor to the reaction. We find that the absorption peak exhibits a dramatic change from 358 to 313 nm with the addition of Cs precursor to the reaction mixture of Pb and Br precursors. Accordingly, we propose that there might be a two-step formation pathway for Cs 4 PbBr 6 NCs. The formation of the Pb−Br bond is the first step, and then, a new reaction takes place after the Cs precursor is involved, which eventually results in the formation of Cs 4 PbBr 6 NCs. The present study provides a new approach to synthesize the Cs 4 PbBr 6 NCs and understand their formation pathway.
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