Synthesis of high-quality CdS, ZnS, and ZnxCd1-xS nanocrystals using metal salts and elemental sulfur

High-quality CdS, ZnS and alloyed ZnxCd1-xS nanocrystals are synthesized in the commonly available coordinating solvent, high boiling-point long-chain amines, using the corresponding metal salts ( such as metal stearate, acetate, chloride, sulfate etc.) and elemental sulfur as the precursors. The obtained CdS and alloyed ZnxCd1-xS nanocrystals possess quantum-confinement wavelength-tunable optical absorption and band-edge emission with photoluminescence quantum yields of 25 - 45%. The photoluminescence spectra are dominated by the band-edge emission without deep-trap emission. Particular interests in this synthetic approach are that cubic zinc-blende CdS and ZnxCd1-xS nanocrystals are formed at high temperatures, and the rapid nucleation and instant termination of the crystal growth process is observed. This nucleation and growth feature makes the reproducible and controllable synthesis of nanocrystals with specific emission wavelengths feasible. The alloy structure of the ZnxCd1-xS nanocrystals is proved by the optical spectra and XRD diffractograms, in which the absorption onset and emission peak shift to shorter wavelength; the diffraction peaks systematically shift toward larger angles with an increase of the Zn molar ratio in the material.