Affiliation: | a Institut für Physik der Universität Rostock, Universitätsplatz, 18051 Rostock, Germany b Vitreous Materials Laboratory, Department of Materials Engineering, Federal University of São Carlos, UFSCar, 13565-905 São Carlos, SP, Brazil c Institute of Physical Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria d S.I. Vavilov State Optical Institute, ul. Babushkina 36-1, 193171 St. Petersburg, Russia |