HF-treated porous silicon (PS) was investigated in situ by photoluminescence (PL) in the red-orange region after treatments in various oxidizing atmospheres. Oxidation in moist air induces a blue shift of the PL spectra with increasing oxidation time. The PL intensity of HF-treated PS decreases after treatment in dry oxygen. The PL intensity of HF-treated PS increases strongly after treatment in water atmosphere for treatment times up to 2 days and decreases for longer times, while the increase is enhanced in the red-orange region of the PL spectra. We found that the PL in the red-orange region of PS is correlated with the initial oxidation process of PS.