Manipulating Reaction Intermediates to Aqueous-Phase ZnSe Magic-Size Clusters and Quantum Dots at Room Temperature

It is not resolved which model describes better the aqueous-phase nucleation and growth of semiconductor quantum dots (QDs), the classical one-step one or the nonclassical multi-step one. Here, we design a room-temperature reaction to trap reaction intermediates in the prenucleation stage of ZnSe QDs (as a model system). We show that the trapped intermediate can transform to magic-size clusters (MSCs) via intra-molecular reorganization and can fragment to enable the growth of QDs. The MSCs exhibit a sharp optical absorption peaking at 299 nm, labelled MSC-299. The intermediate, the precursor compound (PC-299) of MSC-299, is optically transparent at 299 nm and to longer wavelengths. This intermediate forms in various Zn and Se reaction systems. The present study provides unambiguous evidence that the nonclassical and classical pathways are both necessary to explain the nucleation and growth of aqueous-phase QDs, with the former pathway favored more by high reaction concentrations.