Core-shell gold/silver nanoparticles: Synthesis and optical properties

► Stable dispersions of Au-Ag core-shell nanoparticles were prepared in aqueous medium. ► The thickness of the uniform Ag shell was varied from 1.0 to 8.5 nm. ► Below a shell thickness of ∼3 nm the Au cores preserve their optical properties. ► Above 4.0 nm, the resulting sol displays optical properties typical for pure Ag. ► The Cl− ions concentration in solution affects the stability of the bimetallic sol.