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Ultraviolet (UV) light emission with almost the same peak wavelengths from thermally oxidized porous silicon (OPS) (340, 355, and 370 nm) and SiO2 powder (340, 350, and 370 nm) has been observed. Photoluminescence excitation spectra of OPS without Si nanoscale particles (SNP) and those of SiO2 powder are very similar, however, very different from those of the OPS with SNP. Three types of luminescence centers with luminescence wavelengths around 350 nm are responsible for UV light emission, and photoexcitation in OPS with SNP occurs in SNP-as well as in Si oxide layers covering SNP. (C) 1996 American Institute of Physics.