A hybrid approach of forming a stabilizing layer of bonded carbon on porous silicon (PSi) surface by photoassisted reaction of acetylene gas at low temperatures is described. The PSi samples were made by anodization in a HF/H2O2 electrolyte at a current density of 80 mA/cm(2). Samples show a strong luminescence with a peak at 644 4 run. The photoluminescence (PL) intensity shows a very strong quenching under the influence of continuous laser illumination (similar to0.25 W/cm(2), 488 nm). The PSi samples were subjected to flowing acetylene under optical illumination from quartz halogen lamp (20 mW/cm(2)). The PL intensity is initially quenched to very low values (less than 5% of initial value) and then recovers on further exposure to acetylene to a final value similar to30% of the initial value. No quenching is observed on further exposure to laser illumination in ambient air instead an improvement of 15-25% in PL intensity is observed. This behaviour is a good indicator of the formation of a practically stable PSi surface. (C) 2002 Elsevier Science B.V. All rights reserved.