Synthesis and characterization of colloidal II-VI semiconductor nanorods

Colloidal ternary alloy ZnCdSe quantum dots (5∼8 run size) were synthesized by a "single step" reaction using Cd and Zn oleates precursors in a trioctylphosphine oxide (TOPO) solution. Optical properties and structure of these nanocrystals were characterized using photoluminescence (PL), UV-Vis absorption spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). Significant blue shifts from 648 to 567 nm of the PL emission peaks indicated the formation of ternary alloy nanocrystals during the reaction, and the emission wavelength was dependent on reaction time and reaction temperature. The properties were discussed in terms of nucleation and growth processes controlled by the reactivity and diffusion of precursors.; Colloidal ZnCdSe nanorods were synthesized by diffusion of Zn ions into CdSe nanorods in solution at 270°C. CdSe nanorods were prepared using a mixture of tetradecylphosphonic acid (TDPA)/TOPO surfactants at 250°C. The PL quantum yield (QY) of ZnCdSe nanorods was 5∼10 %, which is higher than that from pristine CdSe nanorods (0.6%). XRD and TEM showed that structure of ZnCdSe nanorods was hexagonal structure with ∼6 nm in diameter and ∼13 nm in length. Alloying and compositional disorder during the reaction were determined by spectral shift and line broadening of Raman spectroscopy, UV-Vis absorption spectroscopy and PL. The PL decay was measured using time-resolved photoluminescence (TRPL) and a stretched{09} exponential function, I (t) = Io exp -t/t b , was used to describe PL decay. Comparing CdSe/ZnSe coreshells to alloy ZnCdSe, we find a significant decrease in the beta value (from ∼0.75 to 0.48 ∼ 0.58) which is attributed to compositional disorder in nanorod crystals such as spatial fluctuations of the local Zn concentration. Emission decay time (tau) increases from 173 ns to 270∼500 ns. We speculate that the binding energies of exciton in alloy nanorods increase due to increased localization of exciton by compositional fluctuation, leading to increase luminescence decay time (tau). For additional insight, femtosecond transient absorption has been utilized to study the evolution of the absorption bleaching in the nanorods, which support other results explained by alloying and compositional disorder of ZnCdSe nanorods system.; Gold nanocrystals ∼2 nm in diameter were grown directly on a S 2- rich surface of CdS nanorods using strong Au-S bonding nature. CdS nanorods grew from Au nanocrystal nucleation sites prepared by the reaction of nonstoichiometric precursors in the presence of ethylene diamine. PL was quenched significantly after Au nanocrystals were deposited on CdS nanorods and this effect was attributed to interfacial charge separation between Au nanocrystals and CdS nanorods. Efficient charge separation in Au/CdS nanorods enhanced photocatalytic degradation of the Procion red mix-5B (PRB) dye in aqueous solution under UV light irradiation.