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 degrees 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.