Synthesis Spectrum Properties of High-Quality CdS Quantum Dots

High-quality CdS quantum dots with zinc-blende structure were prepared in noncoordinating solvent 1-octadence (ODE), using N-oleoyl-morpholine as an alternative solvent for sulfur powder, oleic acid (OA) as capping ligand. Sulfur powder could be dissolved in N-oleoyl-morpholine at room temperature. The kinetics of nucleation/growth was monitored via the temporal evolution of optical properties of the as-prepared CdS quantum dots. Various synthetic parameters were systematically investigated, such as growth temperature of 190 degrees C-260 degrees C, OA concentrations of 1.5 mL-2 mL, and the feed molar ratios of (0.5-3) Cd/1S. With increasing feed molar ratio of Cd/S, little trap emission could be observed. The feed molar ratio of 3Cd/1S was suggested to be the optimal synthetic window, together with the amount of OA 1.5 mL and the growth temperature of 210 degrees C. The quantum dots with growth periods ranging from 0 to 900 s at 210 degrees C exhibited their first excitonic absorption peak changing from 359 nm to 429 nm and the corresponding average size moved from 2.26 nm to 4.41 nm. The narrowest PL FWHM we obtained was 16 nm. Typical HRTEM images revealed that the as-prepared CdS quantum dots had narrow size distribution and high crystallinity.