In situ photoluminescence (PL) and transmission IR spectral measurements have been carried out for porous Si (PS) after exposure to thermoelectrons and subsequent exposure to D atoms or D2O. Upon exposure to thermoelectrons the PL band (765 nm) of the PS almost diminished accompanied by the intensity reduction of the IR bands due to Si-Hx (x= 1-3) species. A subsequent D atom exposure resulted in a recovery of the PL band with the formation of Si-Dx bonds. In contrast, D2O exposure gave rise to a new PL band at 650 nm in addition to a 745 nm band accompanied by the emergence of IR bands due to Si-OD and Si-D bonds: the integrated PL intensity after the D2O exposure is 1.2 times larger than the PL intensity of the as-anodized PS. These results suggest that the PL of the PS contains an important contribution from the surface Si-O bonds.