The dynamics of excited carriers in porous silicon were investigated using the near-field heterodyne transient grating method, and the fundamental processes related to light emission were determined. The processes include trapping to surface states and two-body recombination of excited carriers, with trapping being the dominant source of light emission. Since nonlinear processes, namely two-body recombination, are included, it is necessary to measure the pump intensity dependence of the transient responses and to analyze them with a nonlinear differential equation in order to obtain accurate decay times. (c) 2006 Elsevier B.V. All rights reserved.