Evolution of Two Types of CdTe Magic-Size Clusters from a Single Induction Period Sample.

There are two types of colloidal semiconductor nanocrystals (NCs) that exhibit band gap absorption that is relatively sharp compared to conventional quantum dots (QDs). One type displays an absorption doublet, while the other displays an absorption singlet. Here, we report the evolution of the two types of NCs at room temperature from a single CdTe sample extracted during the induction period (IP) prior to nucleation and growth of conventional QDs. The resulting NCs exhibit band gap absorption peaking at ∼371 nm and are magic-size clusters (MSCs), labeled as dMSC-371 and sMSC-371 for the doublet and singlet cases, respectively. We demonstrate that dMSC-371 (with another peak at ∼350 nm) evolves when the sample is incubated. When the sample is dispersed without incubation into a toluene and octylamine mixture, dMSC-371 or sMSC-371 grows depending on the amine amount. We propose that dMSC-371 and sMSC-371 are a pair of polymorphs (with identical CdTe core compositions). The present study brings insight into the formation relationship between dMSCs and sMSCs.