Synthesis and characterization of SiO2-coated mercaptoacetic acid-stabilized CdSe nanocrystals in aqueous solution

Mercaptoacetic acid-stabilized CdSe nanocrystals (NCs) coated with SiO2 shell have been prepared in aqueous solution at room temperature. The results showed that the characteristic UV–Vis absorption peak disappeared, the band-edge photoluminescent (PL) emission greatly increased and the surface state emission decreased after the CdSe core overcoating with SiO2 shell. The absorption spectra of the CdSe/SiO2 composites did not obviously change but the PL spectra continually varied with reaction time during, about, a month. The quantum yield of the CdSe/SiO2 composites was enhanced compared to the CdSe cores. Transmission electron microscopy (TEM) images revealed that multiple nanocores were incorporated in the spheres ranging in diameter mainly from 50 to 100 nm. Very aggregated spheres might be caused by the further hydrolysis of tetraethyl orthosilicate (TEOS). The X-ray diffraction (XRD) patterns also implied that the CdSe NCs had been incorporated in the SiO2 matrix.