Besides the photochromic glasses based on silver halides, especially the cuprous halide containing materials are of practical importance. Due to their high absorption coefficient, the cuprous halides are particularly suited for the preparation of thin photochromic films. Using the sol-gel technique silicon alkoxide based coating solutions with continuously distributed photoactive components were prepared. From these sols, single or multilayer coatings were produced by dipping. The precipitation of the cuprous halide microcrystals as carriers of the photochromic properties of the coatings proceeded during a subsequent heat treatment (temp range of 100-800 degC). Thus is was possible for the first time to produce photochromic coatings with a pronounced darkening and with complete reversibility of the photochromic reactions at room temperatures.
