On the greenish-yellow color of natural Brazilian titanite

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Marco E. Ciriotti
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On the greenish-yellow color of natural Brazilian titanite

Messaggio da Marco E. Ciriotti » lun 08 apr, 2019 14:03

▪ Tolentino, E.L., Dias, C.H., Chaves, M.L.S.C., Krambrock, K., Pinheiro, M.V.B. (2019): On the greenish-yellow color of natural Brazilian titanite. Physics and Chemistry of Minerals, 46, 202-213.

Natural greenish-yellow titanites from two localities in Brazil (Bananal/Capelinha, MG and Xambioá, TO) were characterized by electron paramagnetic resonance (EPR) and optical absorption. Along with vanadyl ions (VO2+) substituting Ti4+, two other paramagnetic centers were identified: the Fe3+ and the Mn2+. For the VO2+, the principal values and orientations of the g and A tensors were derived from a careful analysis of the angular dependence of the EPR spectra. The obtained results, although different to previously reported data, still support the model for the VO2+ bonds to the nearest oxygen (O1) in the TiO6-distorted octahedra. In addition, the titanite optical absorption spectra were analyzed, and the yellow color was ascribed to Fe3+ ↔ O2− ligand–metal charge transfer transitions (LMCT) in the near-ultraviolet, extending to the violet and blue spectral ranges. The VO2+ center seen by EPR was in low concentration and had no visible effect on the color. Finally, γ-irradiation up to 200 kGy and thermal treatments in oxidizing/reducing atmospheres up to 600–700 °C also had no big influence on the dominant yellow color.
Marco E. Ciriotti

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