Effect of Silica Shell on Electronic Excitations Dynamics in Au/SiO 2 Core/Shell Nanoparticles

The electron excitations dynamics in spherical Au/SiO 2 core-shell nanoparticles excited by 150 fs laser pulses at wavelength of 400 nm was studied by femtosecond transient absorption spectroscopy. It is shown that the electron-phonon and phonon-phonon relaxation times in a nanoparticle increase in the presence of SiO (2) dielectric shell. The obtained transient extinction kinetics of NPs was used to fit the theoretical profile with the relaxation temperature of the excitation dynamics of electron and lattice nanoparticles, as well as their environment under the laser pulses action. The electron-phonon coupling and phonon-phonon relaxation constants for Au/SiO (2) NPs and Au NPs have been established. For Au/SiO (2) corehell nanoparticles, the electron-phonon coupling constant was gamma (core/shell) = 5 center dot 1016 W center dot m(-3) center dot K-1, and the heat loss constant was h (core/ shell) = 4 center dot 108 W center dot m(- 2) center dot K- 1. In the case of gold nanospheres, these constants are gamma NPs = 7 center dot 1016 W center dot m(- 3) center dot K- 1 and h (NPs) = 8 center dot 108 W center dot m(-2) center dot K-1, respectively. It is concluded that the SiO 2 dielectric shell prevents the defragmentation of the gold core when it reaches the melting point.