Composition- and Shape-Controlled Synthesis and Optical Properties of ZnxCd1-xS Alloyed Nanocrystals

Composition-tunable ZnxCd1–xS alloyed nanocrystals have been synthesized by a new approach consisting of thermolyzing a mixture of cadmium ethylxanthate (Cd(exan)2) and zinc ethylxanthate (Zn(exan)2) precursors in hot, coordinating solvents at relatively low temperatures (180–210 °C). The composition of the alloyed nanocrystals was accurately adjusted by controlling the molar ratio of Cd(exan)2 to Zn(exan)2 in the mixed reactants. The alloyed ZnxCd1–xS nanocrystals prepared in HDA/TOP (HDA: hexadecylamine; TOP: trioctylphosphine) solution exhibit composition-dependent shape and phase structures as well as composition-dependent optical properties. The shape of the ZnxCd1–xS nanocrystals changed from dot to single-armed rod then to multi-armed rod with a decrease of Zn content in the ternary nanoparticles. The alloying nature of the ZnxCd1–xS nanocrystals was consistently confirmed by the results of high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and UV-vis absorption and photoluminescence (PL) spectroscopy. Further, the shape-controlled synthesis of the ternary alloyed nanocrystals was realized by selecting appropriate solvents. Uniform nanodots in the whole composition range were obtained from TOPO/TOP solution, (TOPO: trioctylphosphine oxide) and uniform nanorods in the whole composition range were prepared from HDA/OA solution (OA: octylamine). The effect of the reaction conditions, such as solvent, reaction temperature, and reaction time, on the PL spectra of the alloyed ZnxCd1–xS nanocrystals was also systematically studied, and the reaction conditions were optimized for improving the PL properties of the nanocrystals.