Novel silicate glasses in the acceleration of hydrogen diffusion for reducing dopant metal ions

Controlling valence state of metal ions doped in glasses, in particular with lower valence, has been widely applied for turning the optical properties. Although hydrogen has been proven effective to reduce metal ions because of its strong reducing capability, the development of silicate glasses doped with lower valency metal ions is still a formidable challenge because of low diffusion rate of hydrogen gas in glass. Recently, the authors studied the reaction of metal ions doped in Na2O-Al2O3-SiO2 glass with hydrogen gas and succeeded in the preparation of the glass that exhibited fast hydrogen diffusion and reduced the metal ions to lower valance states. When the metal ions were doped in glasses containing Al2O3 with Al/Na > 1, the hydrogen gas diffusion coefficient was increased more than two orders of magnitude higher than that for glasses with Al/Na < 1 and the reduction of dopants concurrently caused the formation of Al-OH bonds in the glass. These completely different reductions, occurred depending on the Al/Na concentration ratio, were discussed to relate with the glass structure and the question whether and how the dopants were reduced in glass was elucidated. The obtained results will help to both understand basic science of hydrogen diffusion process in glass and develop new optical devices.