Photonic Materials by the Sol-Gel Process

The sol-gel technique offers a low temperature method for synthesizing amorphous inorganic solids which contain trapped organic molecules with deliberately chosen optical properties. The poor thermal stability of organic molecules has precluded their incorporation in traditional oxide host materials because of the elevated processing temperatures involved with these materials. Using the sol-gel approach, a wide variety of organic molecules have been incorporated in sol-gel matrices and demonstrated that they retain their specific optical properties in the sol-gel environment. Thus, it has been possible to use the sol-gel method to prepare photonic materials which are luminescent or photochromic, which possess nonlinear optical properties or which exhibit laser action. This paper reviews the two principal areas where sol-gel methods are used to produce organic-doped photonic materials. One area of activity involves the utilization of the organic dopants as luminescent probes of the sol-gel process. Examples of matrix rigidity and solvent chemistry changes are shown. The second area concerns the synthesis of new photonic materials whose optical properties are induced by the addition of specific dopants. Significant results involving tunable solid-state lasers, nonlinear optical properties and photochromic materials are presented.