LOCALIZED STATES IN GERMANATE GLASSES - STUDY OF LUMINESCENCE

The nature of electronic states of germanate glasses at the intrinsic absorption threshold is studied by the luminescence method. Three type s of luminescence were observed. A broad luminescence band at 1.8 eV e xcited by ionizing radiation only in pure germania glass is ascribed t o a self-trapped exciton. The already known photoluminescence (PL) ban d at 2.9 eV of the twofold-coordinated germanium centers was observed in germanate glasses obtained under reduced or normal melting conditio ns. The third is the PL band at 2.8 eV, excited in the strong absorpti on range of all the glasses studied. It was observed irrespective of t he redox conditions. The nature of this luminescence is ascribed to lo calized states with the tetragonal 'rutile'-type structure of the shor t-range order of germanate glasses. The luminescence intensity increas es exponentially with decrease of temperature to 4.5 K. The luminescen ce decay takes place in the time range from several ns to 10 ms and it s kinetics are essentially non-exponential (power law t(-1)). The deca y kinetics are almost independent of temperature.