Preparation of luminescent and optical limiting silicon nanostructures by nanosecond-pulsed laser ablation in liquids

Pulsed laser ablations of a silicon rod target in water, hydrogen peroxide water solution and ethanol were performed, varying the laser parameters. The structural and compositional characteristics of the nanoparticles were studied by photoluminescence, micro-Raman, TEM and X-ray photoelectron spectroscopy. A significant change of the nanoparticle structure and of its interface was observed, depending on the solvents used. Mainly very small nanoparticles are formed in all cases. A wide range of crystalline fractions and chemical compositions has been produced by properly modulating the ablation parameters. Even if a weak photoluminescence behaviour has been obtained in almost all the examined cases, a significant nonlinear optical response has been probed by Z-scan technique. The calculated third order refractive index and absorption coefficient are found to be weakly affected by the specific ablation process, and hence almost independent from the structural and compositional characteristics of the nanoparticles. The only marked difference is observed in the comparison between silicon/silicon oxide nanoparticle and pure silicon nanoparticles, the latter being produced in ethanol. More specifically, a one order of magnitude higher refractive index is observed with nanoparticles dispersed in ethanol.