Lower-Temperature Nucleation and Growth of Colloidal CdTe Quantum Dots Enabled by Prenucleation Clusters with Cd–Te Bond Conservation

The reason why heating is required remains elusive for the traditional synthesis of colloidal semiconductor quantum dots (QDs) of II-VI metal chalcogenide (ME). Using CdTe as a model system, we show that the formation of Cd-Te covalent bonds with individual Cd- and Te-containing compounds can be decoupled from the nucleation and growth of CdTe QDs. Prepared at an elevated temperature, a prenucleation-stage sample contains clusters that are the precursor compound (PC) of magic-size clusters (MSCs); the Cd-Te bond formation occurs at temperatures higher than 120 °C in the reaction. Afterward, the PC-to-QD transformation appears via monomers at lower temperatures in dispersion. Our findings suggest that the number of Cd-Te bonds broken in the PC reactant is similar to that of Cd-Te bonds formed in the QD product. For the traditional synthesis of ME QDs, heating is responsible for the M-E bond formation rather than for nucleation.