Origin of the color in cobalt-doped quartz.
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Date
2011
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Abstract
Synthetic Co-doped quartz was grown hydrothermally
in steel autoclaves at the Technological Center of
Minas Gerais (CETEC), Brazil. The quartz samples, originally
yellow in the as-grown state acquired blue coloration
after prolonged heat treatment times at 500°C near the
alpha–beta transition temperature. UV–VIS–NIR absorption
spectroscopy shows the characteristic spectra of Co3+
before heat treatment. After heat treatment, the optical
absorption spectrum is dominated by two split-triplet bands
the Wrst in the near infrared region centered at about
6,700 cm¡1
(1,490 nm) and the second in the visible spectral
range at about 16,900 cm¡1
(590 nm). Both split-triplet
bands are typical for Co2+ ions in tetrahedral coordination
environments. From the absence of electron paramagnetic
resonance (EPR) spectra, we conclude that the Co2+ found
in the optical absorption spectra of the blue quartz is not
due to an isolated structural site in the quartz lattice.
Instead, the blue color is associated with electronic transitions
of Co2+ in small inclusions in which the Co site has tetrahedral symmetry. The non-observation of polarizationdepend
optical absorption spectra is also in agreement with
this model. The results for Co2+ in quartz are diVerent from
Co-bearing spinel and staurolite and other silicates like
orthopyroxene, olivine, and beryls. The formation process
of the color center is discussed.
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Keywords
Synthetic quartz, Electron paramagnetic resonance, Optical absorption
Citation
PINTO, L. C. B. de M. et al. Origin of the color in cobalt-doped quartz. Physics and Chemistry of Minerals, v. 38, p. 623-629, 2011. Disponível em: <https://link.springer.com/article/10.1007/s00269-011-0434-3>. Acesso em: 08 mar. 2017.