Antireflective coatings prepared by sol-gel processing: Principles and applications

Sol-gel processing is a powerful tool to prepare antireflective (AR) coatings on optical surfaces. In this paper the different strategies to obtain antireflective properties are reviewed: porous /4 layers, multilayer interference-type films and index-gradient materials such as "moth eye" structures. The processing of the respective films is described and evaluated; references to respective commercial products on glass substrates are given. AR coatings may have a particularly high importance for transparent ceramics as their index of refraction is significantly higher than that of common glass types. Reflective losses therefore are higher which is especially unpleasant for materials with a yet improvable intrinsic transparency. Recent studies indicate that specific porous /4 layers may exhibit pronounced anti-soiling features. Laboratory experiments as well as outdoor exposure tests were used to demonstrate the dust-repellant properties.