By using gold nanoparticles as the surface seed, SiO₂/Ag core-shell composite nanoparticles were synthesized by chemical reduction method. Their morphology, structure and optical properties were characterized and investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-vis absorption spectra. The results showed that the size distribution of the fabricated composite particles was narrow, silver nanoshells were smooth and complete, and the shell thickness could be controlled. And the optical plasmon resonance became gradually blue-shifted with the increase of the thickness of silver nanoshell. While the silver nanoparticles attached on the silica surface grew, their optical plasmon peak became gradually red-shifted until a complete silver shell was formed.

Key words: silica colloid particle, silver nanoparticle, SiO₂/Ag core-shell particle, plasmon resonance absorption