Origin of the Blue Luminescence in Porous Anodic Alumina Films Formed in Oxalic Acid Solutions

Photoluminescence spectra of porous anodic alumina (PAA) films formed in oxalic acid solutions show a blue emission band peaked around 470 nm, in which the corresponding excitation bands locate at 248 nm, 304 nm, and 360 nm, respectively. With the help of ascertaining the mechanism of this blue luminescence, the roles of the oxalic ions on the optical properties of the PAA films was discussed by using optical absorption spectra. It is suggested that the oxalic impurities with different existing or distributing forms would play important roles on the optical properties of PAA films. The 470-nm blue luminescence band could be attributed to the incorporated oxalic impurities rather than the F⁺ centers existed in the PAA films formed in oxalic acid solutions.