Effects of high-temperature electrolysis on the coloration characteristics and oh-absorption bands in alpha-quartz

Abstract

The effect of high-temperature electrolysis in vacuum on the formation of color centers and on the OH-spectrum in natural α-quartz was investigated with numerous samples of different origin. The transformation of those OH-bands which are thermally unstable with respect to their spectral position into stable OH-bands at longer wavelength is strongly affected by electrolysis and seems to be related to the formation of color centers; it appears to take place at the leading edge of the color cloud. The OH-concentration in the crystal before electrolysis is directly proportional to the intensity of the coloration produced by electrolysis and is inversely proportional to the field induced propagation velocity of the color cloud as it moves from the anode to the cathode. The inverse proportionality of the absorption maxima of the C-band and 2.96-μm OH-band indicate a relationship which is interpreted as oxygen vacancy formation. Prolonged electrolysis in vacuum drastically reduces the integrated OH-spectrum and can virtually eliminate it. Since some of these OH-bands have been shown to be associated with interstitial monovalent impurities, the observed spectral changes give evidence that sweeping of α-quartz along the optical axis is possible through vacuum electrolysis at elevated temperatures. The results are of particular interest with respect to the fabrication of quartz resonators since the Q and radiation sensitivity of quartz resonators are known to be strongly influenced by the presence of impurities.