Change in luminescence properties of porous Si by F₂ and D₂O exposure: In situ photoluminescence, Raman, and Fourier-transform infrared spectral study

In situ photoluminescence (PL), Raman, and infrared (IR) spectra of porous Si (PS) during F₂/D₂O exposures were investigated. F₂ exposure 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 subsequent D₂O exposure, 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.