The investigation of photoluminescence centers in porous alumina membranes

To investigate the origin of blue photoluminescence (PL) in porous alumina membrane, we have prepared an anodic aluminum oxide film with a pore diameter of 40 nm in oxalic acid solution by a two-step anodization process. Our results show that the as-prepared alumina membrane is amorphous and exhibits a broad emission band peaking at around 452 nm with two sub-peaks located at 443 nm and 470 nm. As indicated by the PL excitation spectra, there are two excitation peaks which can account for the sub-peaks observed in the PL emission band. We have proposed that the broad emission band with two sub-peaks can be attributed to two luminescence centers in porous alumina membranes, namely, oxygen defects and oxalic impurities. Furthermore, we have rationalized that the two emission centers show similar influence on the PL band in the blue region based on a simple model.