Reversible Photolysis of Ag Sorbed on Collodial Metal Oxides

The photolysis of Ag sorbed on small particles of ZnO and Ti${\mathrm{O}}_2$ in two allotropic modifications is described, also the preparation of photosensitive surface complexes of this type. Gels of such materials are found to change their diffuse reflecting power for light (relative albedo) permanently upon exposure to radiation of wave-lengths up to approximately 5800A. It is possible to obtain with these materials photographic surface images without microscopically resolvable structure. The dependence of the maximal relative albedo variation (80 percent) upon the Ag concentration is found to be that corresponding to a monolayer of Ag atoms. The albedo change is interpreted as a culminative photolysis of the monolayer on the particles exposed to the radiation. This photolysis is reversible upon contact with traces of ${\mathrm{H}}_2$ ${\mathrm{O}}_2$ or ${\mathrm{O}}_3$. The reversion reestablishes the original photo-sensitive qualities so that the whole process can be repeated many times. A hypothesis of the mechanism of this effect is presented.