Crystallization effect on non-linear optical response of silicate glass and glass-ceramics containing gold nanoparticles

Silicate glasses and glass-ceramics containing gold nanoparticles have been prepared by a conventional melt-quenching method and the subsequent two-step heat treatment processes. The relaxation time of non-linear optical response of the gold nanoparticles has been evaluated from femtosecond pump–probe measurements. The gold nanoparticles are precipitated through a heat treatment. A second heat treatment leads to the precipitation of Li2SiO3 nanocrystals on the gold nanoparticles. The relaxation of non-linear optical response consists of two components; one is a fast relaxation within a few picoseconds, which originates from an electron–phonon coupling process, and the other is a slow relaxation due to a thermal diffusion of excess heat from nanoparticles to the glass matrix. Crystallization does not affect the relaxation of the fast component, while the relaxation time of the slow component decreases with an increase in the degree of crystallinity. We propose that the increased thermal conductivity in precipitated crystals, i.e., Li2SiO3 nanocrystals, leads to the increase in the speed of the relaxation process which works by thermal diffusion from metal particles to the matrix.