Photoluminescence activity in natural silica excited in the vacuum-UV range

We report an experimental study on the optical absorption and photoluminescence detected in samples of natural silica. Our results show that the two emission bands, beta (similar to 3.1 eV) and alpha(E) (similar to 4.3 eV), have an excitation profile in the Vacuum ultraviolet region with a maximum at similar to 7.5 eV. This excitation profile indicates that, in terms of energy levels of the luminescent defect, there is a transition from a ground state, S-0, to a second excited state, S-2 able to excite PL emission, in addition to the well known transition corresponding to the optical absorption band, B-2 beta Our data are in a quantitative agreement with 'ab initio' calculations carried out for a two-fold coordinated Ge defect in SiO2 and exclude a correlation between the S-0 --> S-2 transition and the 7.6 eV E band. (C) 1999 Elsevier Science B.V. All rights reserved.