Experimental results presented in this paper on photoluminescence (PL) and thermal desorption spectroscopy of n-type porous silicon (PS) are consistent with the extinction of the PL emission being due to the creation of free bonds at the surface of the porous layer crystallites. Desorption of hydrogen and SiH$_4$ have been thoroughly investigated. Extinction of PL has been studied after heating the samples in high vacuum and in an Ar atmosphere