Study of the germanium luminescence in silica: From non-controlled impurity to germano-silicate core of telecommunication fiber preforms

We have studed luminescence properties of doped silica with different concentrations of germanium. The basic luminescence parameters such as spectral dependencies, decay kinetics and polarization at different temperatures were measured. Three spectral ranges 3.5-5.5 eV(I), 5.5-7 eV(II), 7-8 eV(III) in the optical transparency range of silica could be chosen from these data. Range I possesses a weak variation of basic parameters of luminescence of the germanium related oxygen deficient center with the change of luminescence center concentration from extremely low in pure silica to the germano-silica core of optical telecommunication fiber preforms. The temperature dependence of luminescence intensity and spectral content including excitation band are more affected by a change of concentration. The deviation of those parameters could be explained mainly within the framework of inhomogeneous broadening and center interaction with varying environment. The changes of decay kinetics and polarization excited in Ranges II and III are also insensitive to the change of concentration but the spectral content is more sensitive to the history of sample preparation, providing bigger changes in spectral bands that could be explained as a result of different surroundings leading to inhomogeneous broadening of the basic parameters. Range III is more affected by a host defect (ODC(I)), manifesting itself through an absorption band at 7.6 eV, by providing recombination mechanisms of luminescence excitation.