Origin of the color in cobaltdoped quartz

Authors: Luiz Carlos B de Miranda Pinto Ariete Righi Fernando Soares Lameiras Fernando Gabriel da Silva Araujo Klaus Krambrock

Publish Date: 2011/05/15

Volume: 38, Issue: 8, Pages: 623-629

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Abstract

Synthetic Codoped quartz was grown hydrothermally in steel autoclaves at the Technological Center of Minas Gerais CETEC Brazil The quartz samples originally yellow in the asgrown 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 splittriplet bands the first in the near infrared region centered at about 6700 cm−1 1490 nm and the second in the visible spectral range at about 16900 cm−1 590 nm Both splittriplet 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 nonobservation of polarizationdepend optical absorption spectra is also in agreement with this model The results for Co2+ in quartz are different from Cobearing spinel and staurolite and other silicates like orthopyroxene olivine and beryls The formation process of the color center is discussedThe authors acknowledge financial support from FAPEMIG CNPq VALE CAPES Gorceix Foundation and Materials Engineering Graduate Program of Federal University of Ouro Preto REDEMAT/CETECUFOPUEMG and acknowledge kindly the suggestions of the referees in special Michail Taran

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