Photoluminescence at 1.9 eV in synthetic wet silica

We report the effects of γ-irradiation on the optical activity of wet synthetic silica samples. As a function of γ-dose, the growth of a composite structure in the 4–6 eV spectral region of the absorption spectrum is observed. This structure can be resolved into two main contributions centered at 5.8 and 4.8 eV, respectively. The first component is usually attributed 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 kinetics, in the γ-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, reaching constant amplitudes, after an initial linear increase, at a dose depending on the OH content. In addition, their ratio is independent of the sample. These results are consistent with a structural model in which the observed optical activity arises from a single-point defect induced by γ-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).