Photoluminescence properties of porous anodic aluminium oxide membranes formed in mixture of sulfuric and oxalic acid

Porous anodic aluminium oxide (AAO) membranes with ordered nanopore arrays were fabricated electrochemically in the mixture electrolytes with various volume ratios of 0.3 M H₂SO₄ and 0.3 M C₂H ₂O₄. Photoluminescence (PL) properties of as-prepared AAO membranes were investigated. It was found that a 290 nm emission was observed in the AAO samples formed in the H₂SO₄ electrolyte and a 325 nm emission in the samples formed in the C₂H₂O ₄ electrolyte, respectively. For the AAO membranes anodized in the mixture electrolytes, both 290 and 325 nm emissions appeared together; moreover, the 290 nm peak was weakened, and the 325 nm peak was enhanced dramatically. It is suggested that the 290 and 325 nm emissions could be attributed to the luminescent centres transformed from sulfuric and oxalic impurities, respectively, and that nonradiative energy transfer occurs between these two kinds of PL centres.