Diffusion and reaction of H2 gas for reducing Eu3+ ions in glasses

Abstract

We have recently developed new Eu2+-doped Na2O–Al2O3–SiO2 glasses by heating precursors in H2 gas, in which Al3+ ions play an important role in reducing Eu3+ to Eu2+. However, the pathway by which the Eu3+ ions are reduced was not established. To address this question, the structural changes involving Al3+ and Eu3+ ions have been elucidated from Magic-Angle Spinning Nuclear Magnetic Resonance (MAS NMR) in solid state and X-ray absorption fine-structure spectroscopies. In the glasses with Al/Na >1, the Al3+ ions form AlO4 units without incorporating Na+ ions for charge compensation, and the Eu3+ ions are coordinated by a network structure comprising AlO4 and SiO4. When heated in H2 gas, the H2 gas molecules diffuse and react with the Eu3+ ions, reducing them to Eu2+ and forming O–H bonds. The diffusion rate of H2 molecules was analyzed from the formation process of O–H bonds; 3.37×10−12 m2/sec at 700°C and 39.5kJ/mol for diffusion coefficient and activation energy, respectively.