In situphotoluminescence (PL), Raman, and infrared (IR) spectra of porous Si (PS) duringF2/D2Oexposures were investigated.F2exposure at 298 K resulted in a peak shift of PL band from 750 to 670 nm with an intensity reduction. IR spectra revealed that the surface hydrogenated Si of the PS was displaced by fluorinated one. By subsequentD2Oexposure, the PL band further shifted to a shorter wavelength with a significant intensity increase: IR bands due to surface oxides as well as SiD and SiOD bonds were observed after the exposure. On the contrary, the average size of the Si crystallites in the PS evaluated from Raman spectra remained almost unchanged throughout the exposures. These results suggest that surface chemistry plays a crucial role in the PL of the PS. ©1998 American Institute of Physics.