Publication: Cause of Color Modification in Tanzanite after Heat Treatment
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Issued Date
2020
Resource Type
File Type
application/pdf
ISSN
14203049
Other identifier(s)
2-s2.0-85089810472
Rights Holder(s)
Scopus
Bibliographic Citation
Molecules. Vol 25, No.16 (2020)
Suggested Citation
Pluthametwisute T., Wanthanachaisaeng B., Saiyasombat C., Sutthirat C. Cause of Color Modification in Tanzanite after Heat Treatment. Molecules. Vol 25, No.16 (2020). doi:10.3390/molecules25163743 Retrieved from: https://hdl.handle.net/20.500.14740/4457
Abstract
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 V3+ to V4+ or Ti3+ to Ti4+ 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. © 2020 by the authors.