The synthesis of CdSe/ZnS core/shell nanocrystals though aqueous phase using the coprecipitation method was reported. The influences of factors such as injection methods and dosages of precursors, reaction duration of water-bathing and the initial CdSe：ZnS molar ratio were discussed. In comparison to the CdSe plain core nanocrystals, the CdSe/ZnS core/shell nanocrystals show much brighter photoluminescence demonstrated by the photoluminescence spectra. The epitaxial growth of the core/shell structures was verified by TEM and XRD.
The comparison of traditional route to the simple synthesis of CdSe semiconductor nanocrystals, with the hydrothermal route, where the reaction temperature can be reached at 220℃, was presented in this paper. The optical properties of the water-soluble CdSe quantum dots from the hydrothermal and traditional were characterized by UV-vis absorption spectra, photoluminescence （PL） spectra and HRTEM techniques. The HRTEM results show that with the increase of the reaction temperature, the naocrystal defects decreased. The UV-vis absorption peak moved to long wave-length with the increase of reaction temperature. The photoluminescence （PL） spectra show that the wavelength of the bright point, the PL quantum yield （QY） increased when the nanocrystal defects decreased. The optical property data confirm that hydrothermal router is a preferable method to traditional route for preparing water-soluble CdSe quantum dots.
