Luminescent Silicon nanocrystals produced by ns pulsed laser ablation

The reduction of Si down to nanoscale introduces a peculiar visible luminescence, surprisingly for a not highly emissive material. This feature is relevant in connection with several application fields (optoelectronics, medicine) and has lead the research towards the development of production methods successful to control the physical and chemical properties of the nanosized Si so as to enhance and tune the luminescence. To this purpose, the laser ablation in liquids is particularly promising since it provides effective controlling parameters (laser photon energy, fluence, repetition rate, liquid reactivity) for the morphology and the structure of Si-related products. Here we report a study of the emission properties of Si-nanocrystals produced by laser ablation in water using the harmonics of a ns pulsed Nd:YAG. The luminescence is investigated by time-resolved technique under a visible-UV tunable laser excitation. The reported results evidence a band centered around 1.9 eV (red band) with a lifetime in the microseconds time scale, with an excitation profile extending all over the visible and UV range. These findings are discussed on the basis of the literature models: quantum confinement of free excitons or localized states at Si/SiOx interface.