Spectral and dynamical study of nonlinear luminescence from silicon nanocrystals excited by ultrashort pulses

We report on the spectral and dynamical properties of photoluminescence (PL) under ultrashort (femtosecond and picosecond) laser pulse excitation in Si nanocrystals prepared by Si+-ion implantation into a silica matrix. We concentrate on the luminescence properties that make it possible to distinguish several luminescence bands within a broad luminescence spectrum. In time-integrated luminescence, saturation-related changes suggest a presence of two different recombination channels connected to the nanocrystal volume states and the nanocrystal–SiO2 interface. The saturation of the luminescence can be explained in terms of Auger recombination. We investigated in detail fast sub-nanosecond luminescence, where significant differences were observed under UV excitation (linear pump-intensity dependence, PL maximum at 450 nm) and for the excitation wavelengths in the visible part of the spectrum (superlinear pump-intensity dependence, broad luminescence band including wavelengths as short as 300 nm). We propose a rate-equations model based on the Auger and radiative/nonradiative recombination to interpret the experimental data.