Silica Coating of Water-Soluble CdTe/CdS Core-Shell Nanocrystals by Microemulsion Method

摘要

We report a synthesis route to prepare CdTe/CdS core-shell nanoparticles (NPs) in aqueous solution. Using Te powder as tellurium source and Na2S as sulfur source, core-shell CdTe/CdS NPs were synthesized at 50 oC. UV-visible and Photoluminescence (PL) spectra are used to probe the effect of CdS passivation on the CdTe quantum dots. As the thickness of CdS shell increases, there is a red-shift in the optical absorption spectra, as well as the photoluminescence (PL) spectra. The broadening absorption peaks and PL spectra indicate that the size distributions of CdTe/CdS NPs widen increasingly with the increasing of CdS coverage. The PL spectra also show that the fluorescence intensity of CdTe QDs will increase when the particles are covered with CdS shell with ratio of S/Te less than 1.0, otherwise it will decrease if ratio of S/Te larger than 1.0. Furthermore, the (CdTe/CdS) @SiO2 particles are prepared by a water-in-oil microemulsion method at room temperature in which hydrolysis of tetraethyl orthosilicate leads to the formation of monodispersed silica nanospheres. The obtained (CdTe/CdS)@SiO2 particles show bright photoluminescence with their fluorescence intensity being enhanced 18.5% compared with that of CdTe NPs. TEM image shows that the diameter of these composite particles is 50 nm. These nanoparticles are suitable for biomarker applications since they are much smaller than cellular dimensions.