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.
The transformation of colloidal semiconductor
magic-size
clusters
(MSCs) from zinc to cadmium chalcogenide (ZnE to CdE) at low temperatures
has received scant attention. Here, we report the first room-temperature
evolution of CdE MSCs from ZnE samples and our interpretation of the
transformation pathway. We show that when prenucleation stage samples
of ZnE are mixed with cadmium oleate (Cd(OA)2), CdE MSCs
evolve; without this mixing, ZnE MSCs develop. When ZnE MSCs and Cd(OA)2 are mixed, CdE MSCs also form. We propose that Cd(OA)2 reacts with the precursor compounds (PCs) of the ZnE MSCs
but not directly with the ZnE MSCs. The cation exchange reaction transforms
the ZnE PCs into CdE PCs, from which CdE MSCs develop. Our findings
suggest that in reactions that lead to the production of binary ME
quantum dots, the E precursor dominates the formation of binary ME
PCs (M = Zn or Cd) to have similar stoichiometry. The present study
provides a much more profound view of the formation and transformation
mechanisms of the ME PCs.
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