Reduction Mechanisms of Cu2+-Doped Na2O–Al2O3–SiO2 Glasses During Heating in H2 Gas

Controlling valence state of metal ions that are doped in materials has been widely applied for turning optical properties. Even though hydrogen has been proven effective to reduce metal ions because of its strong reducing capability, few comprehensive studies focus on practical applications because of the low diffusion rate of hydrogen in solids and the limited reaction near sample surfaces. Here we investigated the reactions of hydrogen with the Cu2+-doped Na2O-Al2O3-SiO2 glass, and found that a completely different reduction is occurring than results reported so far, which is dominated by the Al/Na concentration ratio. For Al/Na 1, on the other hand, the reduction of Cu2+ ions occurred simultaneously with the formation of OH bonds, while the reduced Cu metal moved outwards and formed a metallic film on glass surface. The NMR and FT-IR results indicated that the Cu2+ ions were surrounded by Al3+ ions that fo...