Preparation and characterization of water-soluble jingle-bell-shaped silica-coated cadmium sulfide nanoparticles

Treatment of surface silanol groups with hydrophilic compounds enabled silica-coated cadmium sulfide (SiO2/CdS) nanoparticles of core−shell morphologies to be dissolved in a water/methanol mixture. Size-selective photoetching of the particles was performed by irradiation with monochromatic light at 458 nm, resulting in a blue shift of its absorption onset because of the decreasing size of the CdS. TEM analyses revealed that the SiO2 shell structure was not shrunken by photoetching and that a void space (ca. 2.3 nm) was formed between the CdS core and the SiO2 shell to give a jingle-bell structure. The emission spectra of photoetched particles showed the development of band-gap emission when cadmium ion (Cd2+) was added and the pH was adjusted to 10, whereas the same treatment of original particles gave no peaks assigned to band-gap emission, indicating that the SiO2 shell was sufficiently porous for small ionic species such as Cd2+ to penetrate through the shell and that the photoetched CdS core incorpora...