From the green color of eskolaite to the red color of ruby: an X-ray absorption spectroscopy study |
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| Authors: | Émilie Gaudry Philippe Sainctavit Farid Juillot Federica Bondioli Philippe Ohresser Isabelle Letard |
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| Institution: | (1) Laboratoire de Minénalogie-Cristallographie, Université Pierre et Marie Curie, UMR 7590, 4 place Jussieu, 75252 Paris Cedex 05, France;(2) LURE, Bât 209D Centre Universitaire, B.P. 34, 91898 Orsay Cedex, France;(3) Dipartimento di Ingegneria dei Materiali e dell’Ambiente, Universitá di Modena e Reggio Emilia, Via Vignolese 905, 41100 Modena, Italy |
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| Abstract: | The best known cause for colors in insulating minerals is due to transition metal ions as impurities. As an example, Cr3+ is responsible for the red color of ruby (α-Al2O3:Cr3+) and the green color of eskolaite (α-Cr2O3). Using X-ray absorption measurements, we connect the colors of the Cr
x
Al2−x
O3 series with the structural and electronic local environment around Cr. UV–VIS electronic parameters, such as the crystal field and the Racah parameter B, are related to those deduced from the analysis of the isotropic and XMCD spectra at the Cr L2,3-edges in Cr0.07Al1.93O3 and eskolaite. The Cr–O bond lengths are extracted by EXAFS at the Cr K-edge in the whole Cr
x
Al2−x
O3 (0.07≤x< 2) solid solution series. The variation of the mean Cr–O distance between Cr0.07Al1.93O3 and α-Cr2O3 is evaluated to be 0.015 Å (≈1%). The variation of the crystal field in the Cr
x
Al2−x
O3 series is discussed in relation with the variation of the averaged Cr–O distances. |
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| Keywords: | XAFS Ruby Color of minerals |
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