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The absorption spectra of cobalt-doped anatase TiO2 nanopowders in the infrared and visible ranges have been studied after various oxidative and reductive treatments. The annealing leads to the appearance of the Drude-like contribution in the infrared region and significant change in the absorption in an visible range due to the formation of defects of the oxygen-vacancy-type and Ti3+ ions. The observed additional contribution in the absorption spectra of TiO2:Co nanopowders as compared to the spectra of undoped powders is ascribed to the d–d transitions in ions Co2+. The change in the absorption related to cobalt after annealing is explained by a change in the local environment of Co ions from the octahedral to the tetrahedral environment.
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Mostovshchikova et al. (2019) studied this question.
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