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Optical spectra of Co^(2+) in three synthetic silicate minerals

Taran, Michael N. and Rossman, George R. (2001) Optical spectra of Co^(2+) in three synthetic silicate minerals. American Mineralogist, 86 (7-8). pp. 889-895. ISSN 0003-004X.

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Polarized optical absorption spectra of three synthetic Co-bearing silicates, orthopyroxene, olivine and beryl, were studied at room and liquid nitrogen temperatures. In all three matrices, Co enters octahedral structural sites as the Co^(2+) ion. In accordance with the d^7 electronic energy level diagram, the spectra show three distinct band systems which are assumed to originate from three spin-allowed dd transitions of Co^(2+), ^4T_(1g)(^4F) → ^4T_(2g)(^4F), ^4T_(1g)(^4F) → ^4A_(2g)(^4F), and ^4T_(1g)(^4F) → ^4T_(1g)(^4P). The number of bands is different in different matrices and is regulated by the splitting of electronic states, symmetry selection rules for electronic transitions between them, and Co^(2+) ion distribution between non-equivalent structural sites. Due to a strong preference of Co^(2+) for the M2 site and the greater intensities (oscillator strengths) of electronic dd transitions for Co^(2+) in the M2 site, M2 Co^(2+) bands prevail in the (Mg,Co)SiO_3 orthopyroxene spectra. In olivines, the number of bands is larger than in orthopyroxene due to the combined contribution of both M1 Co^(2+) and M2 Co^(2+) ions. By comparison of the (Mg,Co)_2SiO_4 and Co_2SiO_4 olivine spectra, the bands caused by M1 Co^(2+) and M2 Co^(2+) were distinguished. The spectra of Co-bearing beryls, Be_3Al_2[Si_6O_(18)], prepared by both flux and hydrothermal growth, indicate that Co enters the structure mostly as Co^(2+) in the octahedral Al-site.

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Rossman, George R.0000-0002-4571-6884
Additional Information:© 2001 American Mineralogist. Manuscript received October 13, 2000. Manuscript accepted March 28, 2001. Manuscript handled bye Celia Merzbacher. We thank Jeff Hare for orientating and initially measuring the olivine samples, Jun Ito (deceased), Alexander Lebedev (deceased) and Ed Ustan (San Bernardino, CA) for the donation of samples used in this study and I. AbsWurmbach (Berlin) for discussion of the group theory aspects. The authors are also thankful to two anonymous reviewers, whose remarks and suggestions improved the text. This project was funded in part by the National Science Foundation (U.S.A.), grant NSF EAR-9804871
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Issue or Number:7-8
Record Number:CaltechAUTHORS:20130417-095823406
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Official Citation:Michael N. Taran and George R. Rossman Optical spectra of Co2+ in three synthetic silicate minerals American Mineralogist, July-August, v. 86, p. 889-895
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37982
Deposited By: Ruth Sustaita
Deposited On:17 Apr 2013 19:12
Last Modified:03 Oct 2019 04:53

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