Similar Prenucleation Clusters in Hot-Injection and Heating-Up Approaches to CdS Colloidal Semiconductor Quantum Dots

Colloidal semiconductor quantum dots (QDs) have been synthesized extensively via hot-injection approaches. Using cadmium sulfide (CdS) as a model system, we present compelling evidence for the first time that similar prenucleation clusters (PNCs) appear in both hot-injection and heating-up approaches to CdS QDs. Two reactions were studied. One reaction was in ODE (1-octadecene), with Cd(OA)2 (cadmium oleate) and SODE (sulfur powder dissolved in ODE). The other reaction was in TDO (1-tetradecanol), with Cd(OA)2 and STDO (sulfur powder dissolved in TDO). Furthermore, we reveal that the preformed PNC disappeared faster at a higher temperature and QDs emerged. When PNC-containing samples from the two reactions were dispersed at room temperature, magic-size clusters (MSC-311 displaying optical absorption peaking at ∼311 nm) developed. Accordingly, we conclude that the two-step model proposed by Yu provides more precise explanations to the N/G of QDs and the appearance of MSCs than the LaMer model does.