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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...
Autores principales: | , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
MDPI
2020
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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. |
format | Online Article Text |
id | pubmed-7465713 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2020 |
publisher | MDPI |
record_format | MEDLINE/PubMed |
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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