ESR Study on Silica Exposed to Glow-Discharge Plasma and UV Light

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Abstract
Silica glasses were exposed to glow-discharge plasma of various kinds of gases or to UV light from a low-pressure mercury lamp, and were investigated by ESR. In the case of the plasma exposure, the E' centers are created by UV light emitted from the plasma with photon energy smaller than the optical gap. After a long period of plasma exposure, the density of the E' centers decreases when hydrogen atoms supplied from H2 plasma and/or produced by dissociating OH species in the surface layer move into the inner part of the sample. In the case of the UV-light exposure, illumination time dependence of the E' center density varies with the OH concentration, suggesting that hydrogen plays a role in reducing the E' centers.