Pathway of Room-Temperature Formation of CdSeS Magic-Size Clusters from Mixtures of CdSe and CdS Samples

The synthetic application of prenucleation-stage samples of colloidal semiconductor quantum dots (QDs) is in its infancy. It is shown that when two prenucleation-stage samples of binary CdSe and CdS are mixed, ternary CdSeS magic-size clusters (MSCs) grow at room temperature in dispersion. As the amount of the CdS sample increases, the optical absorption of the CdSeS MSCs blueshifts from approximate to 380 to approximate to 360 nm. It is proposed that the cluster in the CdSe sample reacts with the CdS monomer from the CdS sample. The monomer substitution reaction of CdSe by CdS can proceed continuously; thus, CdSeS MSCs with tunable compositions are obtained. The present study provides compelling evidence that clusters formed in the prenucleation stage of QDs. The clusters are precursor compounds (PCs) of MSCs, transforming at room temperature with the thermoneutrality principle of isodesmic reactions. The nucleation and growth of QDs follows a multi-step non-classical instead of one-step classical nucleation model. Clusters appear in the prenucleation stage of QDs. They are relatively transparent in optical absorption and are the precursor compounds (PCs) of MSCs. For one CdSe prenucleation-stage sample, CdSe MSC-390 transforms to MSC-415; mixed with one CdS prenucleation-stage sample, CdSeS MSCs are seen. The PC-to-PC transformation is assisted by monomer substitution. With enough CdS monomers, the CdSe PC can transform almost entirely to the CdS PC. image