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Advances in Condensed Matter Physics
Volume 2012 (2012), Article ID 873804, 8 pages
http://dx.doi.org/10.1155/2012/873804
Research Article

Color Dependence on Thickness in Topaz Crystal from Brazil

1Faculty of Technology of Sorocaba, Sorocaba, SP, Brazil
2Institute of Physics, University of São Paulo, São Paulo, SP, Brazil

Received 22 March 2012; Revised 18 June 2012; Accepted 9 July 2012

Academic Editor: Mohindar S. Seehra

Copyright © 2012 Waldemar Bonventi Jr et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

It is well known that crystals of topaz from the Eastern Brazilian Pegmatite Province may turn blue by the irradiation with 60Co gamma rays followed by heat treatment. Also, it is known that the sensation of color changes with the thickness of these crystals. The dependence of the color, given by 1931 CIE chromaticity coordinates, with the thickness of the crystal was analyzed. The absorbance used in the calculation of these coordinates was given by the sum of Gaussian lines. The parameters of these lines were determined through the decomposition of the optical absorption spectra in the ultraviolet and visible regions. The decomposition revealed several lines, whose assignment was made considering studies in spodumene and beryl crystals and highly accurate quantum mechanical calculations. The transmittance becomes very narrow with increasing thickness, and the CIE chromaticity coordinates converge to the borderline of the CIE Chromaticity Diagram at the wavelength of maximum transmittance. Furthermore, the purity of color increases with increasing thickness, and the dominant wavelength reaches the wavelength of maximum transmittance.