Competitive relaxation processes of oxygen deficient centers in silica

We report an experimental study on the temperature dependence, from 6 K up to 300 K, of the 4.4 eV emission excited at 7.6 eV via the conversion between two different types of oxygen deficient centers in silica. The photoluminescence undergoes a thermal quenching above 50 K, its amplitude decreasing by a factor of 10, not correlated with changes from 2.1 ns down to 1.4 ns of its lifetime. These experimental features are explained with the occurrence of two nonradiative processes arising from the 7.6 eV excited state: one pumping the 4.4 eV emission and the other accounting for alternative relaxation pathways. The competition between these two rates can be expressed in terms of an Arrhenius law fitting the luminescence quenching with an activation barrier of 29 meV.