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 approximate to 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.

Automated summary

Colloidal semiconductor II-VI metal chalcogenide (ME) magic-size clusters (MSCs) exhibit either a single or double optical absorption. PL-inactive CdS MSC-322 transforms into PL-active CdS MSC-328 and MSC-373 in the presence of acetic acid (HOAc). The transformation process involves monomer substitution for PC-322 to PC-328 and monomer addition for PC-328 to PC-373.