Formation and Transformation of ZnTe and CdTe Magic-Size Clusters Assisted by Their Precursor Compounds

Colloidal semiconductor magic-size clusters (MSCs) remain poorly understood with regard to their formation and transformation. We show that ZnTe MSC-324 (with an optical absorption peak at 324 nm) and MSC-398 evolve in reactions of Zn and Te precursors, while CdTe MSC-371 and MSC-481 develop in reactions of Cd and Te precursors. We propose that MSCs evolve from their precursor compounds (PCs). Chemical self-assembly results in the formation of ZnTe PC-324 and CdTe PC-371, which, respectively, transform to ZnTe PC-398 and CdTe PC-481 via monomer addition. When the ZnTe MSCs are mixed with Cd(OAc)2/OLA (cadmium acetate in oleylamine), the CdTe MSCs also evolve. We further hypothesize that cation exchange occurs on the ZnTe PCs, resulting in CdTe PCs that transform to their counterpart CdTe MSCs. Moreover, ZnTe PC/MSC-324 and CdTe PC/MSC-371 have similar Zn/Cd-to-Te stoichiometries, as do ZnTe PC/MSC-398 and CdTe PC/MSC-481. Accordingly, the Te precursor quantitatively dictates the coassembly of Zn or Cd and Te precursors as well as the monomer addition. The present findings advance the understanding of the initial PC formation, PC-to-PC transformation, PC-to-MSC isomerization, and PC-to-monomer fragmentation.