Electroluminescence spectra and structure of anodic aluminum oxide during its formation in chemically pure water and alcohols

It is found that the thickness of aluminum oxide (Al$_{2}$O$_{3}$) film forming in distilled water linearly increases during 2000 s high-voltage anodization and that its electroluminescence (EL) is reliably detected at the Al$_{2}$O$_{3}$ film thickness of 120 nm. It is shown that Al$_{2}$O$_{3}$ electrolytically formed in distilled water and its deuterium-containing analogue–deuterium water can have an ordered cellular-nanoporous structure identical to the structure formed in aqueous solutions of electrolytes. At the same time, it is found that the existence of this oxide structure is not a necessary condition for its EL. The EL spectra of Al$_{2}$O$_{3}$ in distilled and deuterium water, as well as in water-like electrolytes (ethylene glycol, N,N-dimethylethanolamine, and isopentanol) are recorded for the first time. Considerable discrepancies in the luminescence of aluminum oxide in water and aforementioned alcohols are observed in the range of 400–700 nm. The short-wavelength EL component (at a wavelength near 440 nm) dominates in the EL spectra in the first two liquids, and the long-wavelength component peaking at 625 nm is dominant in the other three cases. Both the luminescence spectral composition and intensity in individual spectral ranges were observed to vary during aluminum anodization.