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Cause of Color Modification in Tanzanite after Heat Treatment

Natural tanzanites usually show strongly trichroic coloration from violet to blue, and brown colors in different directions. However, this characteristic is easily changed to violet-blue dichroism after heat treatment. Moreover, the cause of color modification after heating is still controversial. A...

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Autores principales: Pluthametwisute, Teerarat, Wanthanachaisaeng, Bhuwadol, Saiyasombat, Chatree, Sutthirat, Chakkaphan
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2020
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7465713/
https://www.ncbi.nlm.nih.gov/pubmed/32824379
http://dx.doi.org/10.3390/molecules25163743
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author Pluthametwisute, Teerarat
Wanthanachaisaeng, Bhuwadol
Saiyasombat, Chatree
Sutthirat, Chakkaphan
author_facet Pluthametwisute, Teerarat
Wanthanachaisaeng, Bhuwadol
Saiyasombat, Chatree
Sutthirat, Chakkaphan
author_sort Pluthametwisute, Teerarat
collection PubMed
description Natural tanzanites usually show strongly trichroic coloration from violet to blue, and brown colors in different directions. However, this characteristic is easily changed to violet-blue dichroism after heat treatment. Moreover, the cause of color modification after heating is still controversial. A few researchers have previously suggested that trace amounts of either vanadium or titanium substituted in aluminum site should be the main determinant of color after the heat treatment. Alteration of either V(3+) to V(4+) or Ti(3+) to Ti(4+) may relate to light absorption around 450–460 nm, which is the main cause. UV/vis/NIR absorption spectroscopy and X-ray absorption spectroscopy (XAS), a utility of synchrotron radiation, were applied for this experiment. As a result, the violet-blue absorption band (centered around 450–460 nm) as well as green absorption band (centered around 520 nm) were obviously decreased along the c-axis after heating, and XAS analysis indicated the increasing of the oxidation state of vanadium. This result was well supported by the chemical composition of samples. Consequently, vanadium was strongly suggested as the significant coloring agent in tanzanite after heat treatment.
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spelling pubmed-74657132020-09-04 Cause of Color Modification in Tanzanite after Heat Treatment Pluthametwisute, Teerarat Wanthanachaisaeng, Bhuwadol Saiyasombat, Chatree Sutthirat, Chakkaphan Molecules Article Natural tanzanites usually show strongly trichroic coloration from violet to blue, and brown colors in different directions. However, this characteristic is easily changed to violet-blue dichroism after heat treatment. Moreover, the cause of color modification after heating is still controversial. A few researchers have previously suggested that trace amounts of either vanadium or titanium substituted in aluminum site should be the main determinant of color after the heat treatment. Alteration of either V(3+) to V(4+) or Ti(3+) to Ti(4+) may relate to light absorption around 450–460 nm, which is the main cause. UV/vis/NIR absorption spectroscopy and X-ray absorption spectroscopy (XAS), a utility of synchrotron radiation, were applied for this experiment. As a result, the violet-blue absorption band (centered around 450–460 nm) as well as green absorption band (centered around 520 nm) were obviously decreased along the c-axis after heating, and XAS analysis indicated the increasing of the oxidation state of vanadium. This result was well supported by the chemical composition of samples. Consequently, vanadium was strongly suggested as the significant coloring agent in tanzanite after heat treatment. MDPI 2020-08-16 /pmc/articles/PMC7465713/ /pubmed/32824379 http://dx.doi.org/10.3390/molecules25163743 Text en © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Pluthametwisute, Teerarat
Wanthanachaisaeng, Bhuwadol
Saiyasombat, Chatree
Sutthirat, Chakkaphan
Cause of Color Modification in Tanzanite after Heat Treatment
title Cause of Color Modification in Tanzanite after Heat Treatment
title_full Cause of Color Modification in Tanzanite after Heat Treatment
title_fullStr Cause of Color Modification in Tanzanite after Heat Treatment
title_full_unstemmed Cause of Color Modification in Tanzanite after Heat Treatment
title_short Cause of Color Modification in Tanzanite after Heat Treatment
title_sort cause of color modification in tanzanite after heat treatment
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7465713/
https://www.ncbi.nlm.nih.gov/pubmed/32824379
http://dx.doi.org/10.3390/molecules25163743
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