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

Abstract

Anodic alumina membranes (AAMs) with highly ordered nanochannel arrays wereprepared by anodizing aluminum in acid solutions. X-ray diffraction revealsthe amorphous nature of AAMs. The photoluminescence (PL) excitation spectraof AAMs consist of a broad band centred at 235 nm and a narrow band peakingaround 360 nm under a monitoring wavelength of 470 nm. There are fiveprominent absorption bands (or edges) at 370, 294, 254, 220 and204 nm in the absorption spectra of AAMs prepared in oxalic solution. Withthe increase of the annealing temperature, the intensities of PL andabsorption bands increase first, then decrease, and a blue-shift is found.The photoluminescence and optical absorption in the wavelength range of200 nm to 500 nm are caused by the F+ centres in AAMs. The energy levelsof F+ centres in AAMs are split and a new energy level of 3.35 eVappears due to the amorphous nature of AAMs.