Optical Properties of Ag@TiO₂ and CdS@TiO₂ Core–Shell Nanostructures

Titanium hydroxyacylate has been used as a shell forming agent to form core–shell nanostructures of Ag@TiO₂ (10–40 nm core; 15 nm shell) and CdS@TiO₂ (3 nm core; 1 nm shell) using the reverse micellar route. The low rate of hydrolysis of titanium hydroxyacylate appears to be responsible for the formation of TiO₂ shell. A red shift of 25 nm was observed in the surface plasmon band of silver for Ag@TiO₂ core–shell structures (compared with that of silver nanoparticles) while blue shift of the absorption band CdS@TiO₂ core–shell nanostructures (compared to bare CdS nanoparticles) was observed. CdS@TiO₂ shows a strong quantum confinement effect. Our studies clearly show an increase in the PL intensity of Ag@TiO₂ which we rationalize based on the SERS effect of the Ag nanoparticle. No quenching was observed of the emission band of CdS for the CdS@TiO₂ core–shell nanostructures.