Photoluminescence (PL) measurements were carried out on the porous Si layers kept in the HF solution. The PL peak around 700 nm, usually observed in the PL spectrum of the porous Si layer in the air, was no longer detected. This evidence suggests that the origin of the visible light luminescence from the porous Si layer in the air is different from that in the HF solution and may be associated with the presence of oxygen at the surface. Furthermore, it is interesting to find the cyclic shifts in the PL spectra between green and orange by turning the light on and off to illuminate the porous Si layer in the HF solution. This unique behavior is attributed to photochemical etching under illumination and chemical etching of the porous Si layer in the dark. ©1995 American Institute of Physics.