Luminescence of nanoporous anodic oxide obtained from rare earth doped aluminum

Abstract

Anodizing of aluminum foil with cerium (0.01 at. %) and europium (0.01, 0.05, 0.8 at. %) additives carried out in a multi-component electrolyte (a mixture of oxalic, citric, boric acids and isopropyl alcohol) resulted in formation of nanoporous anodic aluminum oxide (AAO). Their microstructure and photoluminescent properties of AAO were investigated. Doping of aluminum with 0.01 at. % Ce and Eu resulted in increasing intensity of the main luminescence band (380–700 nm) of the obtained oxides compare with that of undoped alumina. This was due to increase in the number of bonds of rare-earths-O-Al, and, accordingly, structural defects (F-centers) in aluminum oxide. The shift of the peaks of the main band, observed at different excitation wavelengths (330, 366, 394 nm), is explained by the different lengths of these bonds causing different energy gaps of the indicated defects. The effect of europium as activator on the luminescent properties of AAO is most pronounced in comparison with cerium. A comparison of the spectra of oxides obtained from Al alloys with different amounts of Eu (0.01, 0.05, 0.8 at. %) showed a decrease in the intensity of their luminescence. A detailed analysis of the emission spectra showed that luminescence of the AAO matrix and the intracenter f–f transitions of rare-earths ions overlap each other. This phenomenon was especially strongly observed on the AAO of the alloy with 0.8 % Eu at excitation wavelength of 250 nm.