Photoluminescence (PL) of annealed porous silicon (PS) without and with nitrogen passivation has been investigated. The un-nitridated PS emits intense blue and green light, while that with passivation, emits only blue light and its intensity increases obviously. It is found that the PL intensity of the nitrified PS decreases with increasing temperature from 300 degrees C to 700 degrees C, but increases drastically after annealing at 800 degrees C and 900 degrees C, which might be due to the formation of Si-N bonds that passivates the non-radiative centers (Si dangling bonds) on the surface of PS samples. However, the intensity of the un-nitridated PS decreases continuously with increasing temperature from 300 degrees C to 900 degrees C, which might be due to desorption of hydrogen. (c) 2006 Elsevier Ltd. All rights reserved.