Spectroscopic evidence of a core–shell structure in the earlier formation stages of Au–Ag nanoparticles by pulsed laser ablation in water

Mixed Au–Ag nanoparticles were obtained by pulsed laser ablation of metallic targets, subsequently mixing and re-irradiating different volumes of each nano-colloid. The study of these colloids after different irradiation times, performed by spectral analysis in the plasmonic resonance (PR) region, allows us to ascertain that solid solutions of Ag into Au nano-crystals are obtained after an initial formation of Aucore–Agshell nanoparticles. These findings are corroborated by fitting the PR spectra with a simulation model based on the Mie-Gans theory. X-ray photoelectron spectroscopy and transmission electron microscopy data support these results and their interpretation.