Lai-Jun Zhang,Xing-Can Shen,Hong Liang,Jia-Ting Yao
Four families of magic-sized ZnSe quantum dots (ZnSe MSQDs) with the first exciton absorption peaks at 280 nm (F280), 291 nm (F291), about 319 nm (F319), and 347 nm (F347) were synthesized using fatty amine−H2Se complex as selenium precursor via noninjection one-pot or hot-injection approaches. The formation, growth, and transformation of these families of ZnSe MSQDs were monitored mainly by ultraviolet−visible absorption spectroscopy. Relatively pure F291 and F347 were obtained via the combination of hot-injection technology with purification treatment and were further characterized using mass spectroscopy, infrared spectroscopy, fluorescence spectroscopy, transmission electron microscopy, and X-ray powder diffraction. F291 and F347 are speculated to be [(Zn7Se7)(OLA)2(OA)] (OLA = oleylamine, OA = octylamine) and [(Zn16Se15)(OLA)7], respectively, by analyzing the corresponding mass and the infrared and absorption spectra; both emit narrow exciton fluorescence with relatively small stokes shift of 9 and 2 nm, respectively. Ultrafine ZnSe nanorods with a diameter of about 1.7 nm formed via oriented attachment of F347 were observed using transmission electron microscopy. Fatty amine−H2Se complex has been demonstrated to be a simple, phosphine-free, low-cost, and effective selenium precursor for the synthesis of ZnSe MSQDs or regular quantum dots (RQDs).
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.
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