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Published February 2007 | public
Journal Article

Thermochromic and photochromic behaviour of "chameleon" diamonds

Abstract

Chameleon diamonds typically change color from greyish-green to yellow when they are heated or cooled (thermochromic behaviour) or kept in the dark (photochromic behaviour). Those diamonds are type Ia with A aggregates largely dominating the nitrogen speciation. They contain moderate to high amounts of hydrogen, in addition to some isolated nitrogen and traces of nickel. Their UV Visible spectrum comprises the continuum typical of type Ib material, the 480 nm band and a broad band centred around 800 nm. It is mainly modified in the red part of the visible spectrum when the color change occurs. We here propose an electronic model consistent with all observed color behaviours, based on the premise that yellow is the stable color whereas green is the metastable one. The chameleon effect is possibly linked to a nitrogen–hydrogen complex.

Additional Information

© 2006 Elsevier B.V. Received 9 November 2005; received in revised form 19 July 2006; accepted 21 August 2006. Available online 4 October 2006. The authors wish to thank the many private parties who loaned chameleon diamonds. Much of the early stages of this work were conducted at the Gemological Institute of America at the time in Santa Monica, CA, with the support of Dr. James E. Shigley and Mr. Thomas Moses and several other colleagues. The SanaDiam Company, Antwerp, Belgium, loaned us a chameleon rough. We want to thank also Chris Ewels for useful discussions, and two anonymous reviewers for constructive comments.

Additional details

Created:
August 22, 2023
Modified:
October 23, 2023