We report a detailed study of red photoluminescence decay in porous si
licon at temperatures 10-300 K. We concentrate on the slow component (
similar to 10(-4) s) which originates in the recombination of carriers
trapped in the surface localized states. Analysis of the experimental
data shows that photoluminescence dynamics is dominated by a thermall
y activated nonradiative process and brings new information on its mic
roscopic origin.