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 core-hell nanoparticles, the electron–phonon coupling constant was γ _core/shell=5· 10^16 W· m^-3· K^-1 , and the heat loss constant was h_core/shell=4· 10^8 W· m^-2· K^-1 . In the case of gold nanospheres, these constants are γ _NPs=7· 10^16 W· m^-3· K^-1 and h_NPs=8· 10^8 W· m^-2· 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.