Coupling effects and ultrafast third-order nonlinear optical behavior in ion-implanted silicon quantum dots and platinum nanoclusters

Third-order nonlinear optical properties exhibited by ion-implanted hybrid systems integrated by Silicon quantum dots and Platinum nanoclusters embedded in a Silica host matrix are reported. Femto-, pico- and nano-second pulses were employed as optical sources with excitation wavelengths at 830 nm, 355 nm and 532 nm, respectively. Transmission electron microscopy studies revealed sizes between 3 and 7 nm for Si quantum dots and 0.5–4 nm for Pt nanoclusters. Quantum confinement effects in this nanoscale seem to dominate the physical properties of the nanostructures and they must be taken into account to describe the interaction of intense laser beams with the hybrid nanocomposites. Femtosecond Z-scan studies showed a strong nonlinearity provided by the Si quantum dots influence, with no important contribution from the Pt nanoparticles to the nonlinear absorption and positive refractive index exhibited by the sample at 830 nm wavelength. Picosecond two-wave mixing experiments with self-diffraction indicate an enhancement close to one order of magnitude at 355 nm compared to the 532 nm wavelength of excitation. The picosecond results can be explained from the active participation of Pt nanoclusters together with Si quantum dots which can be efficiently excited at shorter wavelengths to reach higher electronic states above their energy band gaps. This selectable behavior by changing wavelength and pulse duration of excitation can be useful for tuning multifunctional operations performed by all-optical nanodevices.