1. Institut für Physikalische Chemie WWU Münster Corrensstraße 28/30 48149 Münster Germany
2. Department of Materials Engineering Vitreous Materials Laboratory Federal University of São Carlos CP 676 13565-905 São Carlos SP Brazil
3. Institut für Anorganische und Analytische Chemie WWU Münster Corrensstraße 28/30 48149 Münster Germany
4. Instituto de Física de São Carlos Universidade de São Paulo São Carlos SP 13566-590 Brazil