Fabrication, characterization, and photoluminescence properties of highly ordered TiO₂ nanowire arrays

Highly ordered TiO₂ nanowire arrays were prepared in anodic alumina membranes by a sol-gel method. The nanowires are single-crystalline anatase phase with uniform diameters around 50 nm. At room temperature, photoluminescence (PL) measurements of these TiO₂ nanowire arrays showed a visible broad band with three peaks, which were located at about 425, 460, and 530 nm that are attributed to self-trapped excitons, F, and F⁺ centers, respectively. A model is also presented to explain the PL intensity drop-down of the TiO₂ nanowire arrays embedded in the alumina membrane: the blue PL band of the anodic alumina membranes arises from the F⁺ centers on the pore walls, and the TiO₂ nanowires first form in the center area of the pores and then extend to the pore walls.