Transient visible-UV absorption in beta irradiated silica

We performed optical absorption measurements in the range 1.24-6.2 eV on commercial silica samples during and after room temperature beta-irradiation. Absorption is induced from 1.3 up to 5.5 eV and can be resolved with different bands. Two band structures peaked at 2.3 and 4.2 eV are found in natural silica but not in synthetic silica and are attributed to impurity related defects. Absorption at energy >4.2 eV shows an ubiquitous band at 5.7 eV attributed to E' centers, and a band at 4.7 eV in synthetic samples attributed to non-bridging oxygen hole centers. Transient absorption is observed after irradiation in the spectral range above 3.0 eV with a reduction greater than 30% in a time scale of the order of few hours. A transient band peaked at 4.1 eV is detected both in natural and synthetic samples and is attributed to intrinsic centers. These transient effects are ascribed to relaxation of optically active defects by reaction with diffusing atoms or molecules released during irradiation. (C) 2003 Elsevier B.V. All rights reserved.