Diffusion and reaction of H2 gas for reducing Eu3+ ions in glasses. (June 2017)

• Record Type: Journal Article
• Authors: Nogami, Masayuki; Quang, Vu Xuan; Nonaka, Takamasa; Shimizu, Tadashi; Ohki, Shinobu; Deguchi, Kenzo
• Is Part Of: Journal of physics and chemistry of solids. Volume 105(2017)
• Page Start: 54
• Page End: 60
• Publication Date: 2017-06
• Subjects: Rare-earth -- Eu2+ -- Eu3+ -- Valence control -- Glass -- Hydrogen -- Diffusion; Solids -- Periodicals; Solides -- Périodiques; Solids; Periodicals; 530.41
• DOI: 10.1016/j.jpcs.2017.02.007
• Languages: English
• ISSNs: 0022-3697

Abstract

Abstract: We have recently developed new Eu 2+ -doped Na2 O–Al2 O3 –SiO2 glasses by heating precursors in H2 gas, in which Al 3+ ions play an important role in reducing Eu 3+ to Eu 2+ . However, the pathway by which the Eu 3+ ions are reduced was not established. To address this question, the structural changes involving Al 3+ and Eu 3+ 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 Al 3+ ions form AlO4 units without incorporating Na + ions for charge compensation, and the Eu 3+ 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 Eu 3+ ions, reducing them to Eu 2+ 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 m 2 /sec at 700 °C and 39.5 kJ/mol for diffusion coefficient and activation energy, respectively. Graphic abstract: Fluorescence of the well-controlled Eu 2+ and Eu 3+ ions in aluminosilicate glasses. Eu 3+ ions doped in as-prepared glass are reduced to Eu 2+ by heating in H2 gas. Fluorescence is changed from red (Eu 3+ ) emission to white/blue (Eu 2+ ) one.