Effects of thermal treatment on the third-order optical nonlinearity and ultrafast dynamics of Ag nanoparticles embedded in silicate glasses

Panel (a) indicates that the fast decay process is accelerated and its amplitude ratio increases with thermal treatment, which is quite different from our previous report in which heat treatment caused an increasing relaxation time related to the electron-surface scattering. The fast relaxation time is much lower than the electron-phonon relaxation time of bulk Ag (0.85 ps) and Ag nanoparticles with radius of 2.1 nm (0.6 ps), but close to electron-electron relaxation time of Ag film (350 fs) and Ag nanoparticle with radius of 2.1 nm in a BaO-P2O5 matrix (0.2 ps). Therefore, the fast relaxation process includes both the electron-electron relaxation and the electron-phonon relaxation. We also observed an accelerated relaxation in Ag:Si3N4 nanocermets after annealing, which was mainly attributed to the intensification of the coupling between electrons and phonons due to the diminishing of the detuning of the electronoscillation phonon resonance overlap. In this Letter, the accelerated relaxation was attributed to an increase of the electron-phonon coupling through the process of treelike Ag nanoparticle aggregation due to inter-nanoparticle interactions as shown in Panel (b).