Photoluminescence and optical absorption caused by the F+ centres in anodic alumina membranes

Anodic alumina membranes (AAMs) with highly ordered nanochannel arrays were prepared by anodizing aluminum in acid solutions. X-ray diffraction reveal s the amorphous nature of AAMs. The photoluminescence (PL) excitation spect ra of AAMs consist of a broad band centred at 235 nm and a narrow band peak ing around 360 nm under a monitoring wavelength of 470 nm. There are five p rominent absorption bands (or edges) at 370, 294, 254, 220 and 204 nm in th e absorption spectra of AAMs prepared in oxalic solution. With the increase of the annealing temperature, the intensities of PL and absorption bands i ncrease first, then decrease, and a blue-shift is found. The photoluminesce nce and optical absorption in the wavelength range of 200 nm to 500 nm are caused by the F+ centres in AAMs. The energy levels of F+ centres in AAMs a re split and a new energy level of 3.35 eV appears due to the amorphous nat ure of AAMs.