Development of aqueous-phase CdSeS magic-size clusters at room temperature and quantum dots at elevated temperatures

Little is known about the synthesis of colloidal ternary semiconductor magic-size clusters (MSCs) and quantum dots (QDs) in an aqueous environment. We report here the first synthesis of aqueous-phase CdSeS MSC-380 (displaying sharp optical absorption peaking at ~ 380 nm) at room temperature and QDs at elevated temperatures. The reaction contains CdCl₂·2.5H₂O, 3-mercaptopropionic acid (MPA, HS−(CH₂)₂−COOH), selenourea (SeU, NH₂−C(Se)−NH₂), and thioacetamide (TAA, CH₃−C(S)−NH₂). Prior to the nucleation and growth (N/G) of QDs, there are clusters formed at 25 °C. The prenucleation-stage clusters are the precursor compound of CdSeS MSC-380 (PC-380). The PC is relatively transparent in optical absorption; in the presence of a primary amine butylamine (BTA, CH₃−(CH₂)₃−NH₂), the PC transforms to absorbing CdSeS MSC-380. At 80 °C, the PC decreases and the N/G of CdSeS QDs appears. The present study paves the way to the aqueous-phase synthesis of ternary CdSeS MSCs and QDs, providing an in-depth understanding of the cluster formation in the prenucleation stage of CdSeS QDs.