Comparison of UV optical absorption and UV excited luminescence behaviours in Ge doped silica under H2 loading or CWUV laser irradiation

We compare the CW 244 nm laser induced absorption and photoluminescence excitation changes in Ge and Ge-P doped silica glass according to H, loading. Under H-2 loading only, the absorption does not change but the luminescence excitation intensity decreases by 60%. For samples not H-2 loaded, luminescence excited in the UV range is annihilated by the laser irradiation but not the absorption in the same UV range. During UV irradiation of H-2 loaded samples most of the luminescence excited in the UV range disappears whereas UV absorption behaves differently. In that way, we show that defects giving rise to luminescence exhibit a weak contribution to the absorption spectrum. In particular, there are two different oxygen deficient centres: one absorbing at 5 eV and another one giving rise to luminescence under 5 eV excitation. Due to some correlations existing sometimes between absorption and luminescence, we suggest that luminescence is quenched by trapping of electrons produced by 5 eV absorbing defects. In addition, the use of a CW laser allows us to observe two successive one-photon absorption steps for accounting for the absorption change: a singlet to singlet transition and then an ionisation. (C) 2002 Elsevier Science B.V. All rights reserved.