We present results of the investigation of spectrally resolved photolu
minescence decay in porous silicon on the time interval which spans se
ven orders of magnitude. The luminescence decay can be interpreted in
terms of a fast bimolecular recombination of free carriers in the core
of silicon nanocrystallites and of a slow recombination of localized
carriers in the surface states. The etching time of the samples has an
effect on the relative weight of both components and on the dynamics
of the slow recombination. We discuss the dependence of relevant param
eters on the etching time of the samples.