Recent Progress in Inorganic Photochromism
J. Montero, S. Kim and L. Österlund.
Division of Solid-State Physics, Department of Materials Science and Engineering, The Ångström Laboratory, Uppsala University, P.O. Box 35, SE-751 03 Uppsala, Sweden.
It is well-known that transition metal oxides, such as tungsten oxide, exhibit photochromic properties. The general conclusion from previous studies on these materials relates the photochromic behavior to the presence of hydrogen of atmospheric origin, and desorption of oxygen during photo-darkening. However, mechanistic understanding of the elementary steps remains unclear. In most of these oxides, the photochromic contrast is very small, and the darkening/bleaching dynamics is very slow. In recent years, it was discovered that oxyhydride (or oxide-hydride) materials, based on rare-earth elements, exhibit pronounced photochromic properties. In these class of materials, the hydride and oxide anions coexist. These oxyhydrides have been shown to be stable in air, being able to retain hydrogen, even when subjected to relatively high temperatures. Moreover, rare earth oxyhydrides exhibit very good photochromic optical contrast, dynamics and stability, and could therefore be attractive alternative to conventional organic photochromic dyes. In this talk, our recent research in the field on photochromic oxyhydrides will be discussed.