Comparison of UV optical absorption and UV excited luminescence behaviours in Ge doped silica under H 2 loading or CW UV 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 2 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.