Silver-doped silica colloidal nanoparticles.: Characterization and optical measurements

Silver clusters are obtained on the surface of nanosize silica hydrosols by photoreduction of silver nitrate, induced by visible laser irradiation. The formation of Ag-doped silica colloidal particles is confirmed by the UV–visible absorption spectra, which exhibit a large plasmon resonance band at about 410 nm, similar to that observed in pure silver hydrosols, and by the quenching of the fluorescence intensity. These colloids represent suitable substrates for surface-enhanced Raman scattering (SERS), showing stability and enhancement factors comparable with those obtained in pure silver hydrosols. The simplicity of the procedure and the absence of reducing agents represent significant advantages of this method.