A simple chemical etching of silicon substrates in NaNO2-HF solutions allows us to obtain homogeneously luminescent surfaces when these substrates are mechanically abraded by sand blasting. A comparative study of porous silicon prepared from non-abraded and sand-blasted wafers by IR spectrometry and thermal desorption spectrometry experiments is performed vs. etching time. The hydrogen concentration is eight times higher in sand-blasted wafers and the configurations of the Si-H bonds are different.