Optical properties of anodic aluminum oxide produced in a complex electrolyte

Abstract

Features of the absorption, transmission, photoluminescence, and infrared (IR) spectra of anodic aluminum oxide (AAO) formed in a complex electrolyte and annealed at 800, 900, 1000, and 1300°C are investigated. The variations in the phase composition changes of the anodic aluminum oxide are reflected in the respective features of its optical properties. A decrease in the transmission coefficient in the visible range of the spectrum is shown for the phase series: amorphous AOA → γ-Al2O3, γ-, θ-, δ-Al2O3 mixture → α-Al2O3. It is established that the highest absorption coefficient is characteristic of α-Al2O3, and the amorphous samples are the most transparent in the visible range. An intensive luminescence band in the red region of the spectrum with maxima at 678 and 694 nm is found for α-Al2O3. The emergence of this band is explained by the presence of octahedrally coordinated Mn+4 and Cr+3 impurity ions in the structure. A luminescence band at 700–800 nm is observed for the mixture of low-temperature phases. Intense luminescence in the region 350–500 nm is found for amorphous AAO and γ-Al2O3.