Origin of the blue and red photoluminescence from aged porous silicon

Two-peak photoluminescence (PL), blue and red, is obtained in the long-time aged porous silicon samples that were initially anodized under ${\mathrm{Ar}}^{+}$ 488 nm laser illumination. Static and dynamic photoluminescence, photoluminescence excitation, and Fourier transformation infrared absorption and reflection spectra are studied. It is found that the weight of blue PL increases with increasing the power intensity of the laser used during sample preparation. A good monoexponential microsecond decay over three decades with lifetime of about 5.3 μs is reported. Infrared spectra are quantitatively studied to reveal the influence of the illuminating laser during anodization on the samples and the relationship between the oxidation states of the porous silicon and the blue and/or red photoluminescence. It is suggested that the blue PL in these aged samples comes from the nanometer $c-\mathrm{S}\mathrm{i}$ core, while the red PL originates from the oxide surface.