Photoluminescence at 1.9 eV in synthetic wet silica

We report the effects of gamma -irradiation on the optical activity of wet synthetic silica samples. As a function of gamma -dose, the growth of a com posite structure in the 4-6 eV spectral region of the absorption spectrum i s observed. This structure can be resolved into two main contributions cent ered at 5.8 and 4.8 eV, respectively. The first component is usually attrib uted to an optical transition of the E' centers. The second one is able to excite an emission band centered at 1.9 eV. The analysis of the growth kine tics, in the gamma -dose range 20-1000 Mrad, of both emission at 1.9 eV and absorption at 4.8 eV shows that these two bands change in a similar way, r eaching constant amplitudes, after an initial linear increase, at a dose de pending on the OH content. In addition, their ratio is independent of the s ample. These results are consistent with a structural model in which the ob served optical activity arises from a single-point defect induced by gamma -irradiation. Moreover, based on the correlation with the OH content in our samples, we suggest that the principal candidate for this point defect is the non-bridging oxygen hole center(HBOHC). (C) 2001 Elsevier Science B.V. All rights reserved.