Photoluminescence of Anodic Oxide Films on Aluminium

Abstract

A wide variety of anodic oxide films were investigated from the photoluminescent point of view. It was found that the phenomenon of photoluminescence appears only on the films anodically formed in organic acids instead of inorganic acids. In particular, thick oxalic acid films formed in low electrolyte concentration, with high current densities on high purity aluminium, gave intense photoluminescence. The luminescent centres were presumed to be the carboxylate ions which had been incorporated in the films during anodisation.

Luminescence properties of oxide coatings on aluminum alloys

“…It was assumed [2, 3] that the photoluminescence is associated with the adsorption of H 2 O by active centers (defects) on the oxide film surface. Later studies of anodic alumina films produced in various electrolytes and under different anodizing conditions showed [4,5] that the emission intensity is considerably higher when solutions of organic acids are used. It was widely concluded that the luminescence centers are carboxyl groups that are embedded in the oxide films during the anodizing process [6].…”

“…The thickness of the protective coatings (oxide films) produced in the course of all the processing stages was 35-50 μm. Within the different groups the samples were denoted as follows: (1) only anodized, (2) anodized and treated by electrophoresis, (3 and 4) completed the first two stages and processed by suspensions based on nanocarbon (3) or metal oxides (4). The samples with preliminary processing of the rolled metal surface differing from the standard treatment are denoted by 1 * and 2 * .…”

“…Photoluminescence excitation spectra of anodic alumina samples(1)(2)(3)(4) produced by anodizing in different electrolytes based on oxalic (a, d), sulfuric (b, e), and tartaric-sulfonic (c, f) acids with λ det = 410 (a-c), 470 (d, f), and 510 nm (e); 1 and 1 * are samples after anodizing, 2 and 2 * after anodizing and electrophoresis, 3 and 4 after the first two stages and treatment with suspensions based on carbon (3) and metal oxides (4).…”

Photoluminescence of f-centers in films of anodic alumina

“…It is known that anodic alumina films have fairly strong photoluminescence, the characteristics of which depend substantially on the composition of the electrolyte used to prepare them [5]. Over the last three decades, various models have been proposed to explain the photoluminescence of anodic alumina films.…”

“…Over the last three decades, various models have been proposed to explain the photoluminescence of anodic alumina films. Thus, luminescence mechanisms have been proposed for samples of anodic alumina formed in oxalic acid electrolytes which involve both residues of oxalic impurities [5][6][7] and the presence of F + -and F-centers [8,9]. It has been shown [10][11][12] that the photoluminescence of anodic alumina is caused by the joint action of F + centers and impurities in the form of residues of the oxalic acid electrolyte.…”