Smart Optical Materials by Sol-Gel Method
by R. Reisfeld
Dept. of Inorganic and Analytical Chemistry , The Hebrew University, Jerusalem 91904, Israel

Tunable Laser samples prepared by the sol-gel method 

Electrochromic glasses prepared by the sol-gel method Electrochromism relates to a change of the transparency of a given material upon the application of a small voltage. The phenomenon has been extensively studied because of its extreme importance in architectural and  automotive markets. In principle an electrochromic device consists of a  two transparent conductive glass (1) , an electrolyte (3), an electrochromic material (4),  and a counter electrode (2). In general the reaction leading to darkening and bleaching of the glass is a result of electron transfer accompanied by ion insertion or extraction at the counter electrode layer. In the cases of tungsten oxide the reaction can be summarized as follows: Colorless   colored Here colorless hexavalent tungsten oxide is reversibly reduced to a compound of mixed valence, partly having pentavalent tungsten in the colored state film.

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In future the electrochromic windows will be massively applied for energy saving in buildings and cars in order to prevent the indoor heating by sun.
During the last ten years the global temperature has risen by several degrees and a relatively inexpensive way of prevention of extra heat may become vital.

The most common way of deposition of electrochromic films on ITO (Indium Tin Oxide) conductive glasses used today, is sputtering or evaporation of tungsten oxide. This process has to be performed in vacuum and/or high temperatures and is quite expensive and energy consuming.

Electrochromic films of tungsten oxide can be prepared easily by the sol-gel method at relatively low temperature. The other functional layers including the counter electrodes ( usually TiO2-CeO2 ) as well as the solid electrolyte can be also made by the same technique. Thus, the entire solid state electrochromic device can inexpensively be made by using sol-gel methods.

We have widely investigated  speed and electrochromic response in relationship to many parameters affecting the device efficiency and stability. Optimum conditions for a viable electrochromic device operation were established.