Direct and Indirect Evolution of Photoluminescent Semiconductor CdS Magic‐Size Clusters through Their Precursor Compounds.

Colloidal semiconductor II–VI metal chalcogenide (ME) magic‐size clusters (MSCs) exhibit either an optical absorption singlet or doublet. In the latter case, a sharp photoluminescence (PL) signal is observed. Whether the PL‐inactive MSCs transform to the PL‐active ones is unknown. We show that PL‐inactive CdS MSC‐322 transforms to PL‐active CdS MSC‐328 and MSC‐373 in the presence of acetic acid (HOAc). MSC‐322 displays a sharp absorption at ≈322 nm, whereas MSC‐328 and MSC‐373 both have broad absorptions respectively around 328 and 373 nm. In a reaction of cadmium myristate and S powder in 1‐octadecene, MSC‐322 develops; with HOAc, MSC‐328 and MSC‐373 are present. We propose that the MSCs evolve from their relatively transparent precursor compounds (PCs). The PC‐322 to PC‐328 quasi‐isomerization involves monomer substitution, while monomer addition occurs for the PC‐328 to PC‐373 transformation. Our findings suggest that S dominates the precursor self‐assembly quantitatively, and ligand‐bonded Cd mainly controls MSC optical properties. [ABSTRACT FROM AUTHOR]