VISIBLY PHOTOLUMINESCENT SILICA AEROGELS

Treatment of silica aerogels with microwave-energized reducing gases i nduces permanent, visible photoluminescence in the material. The emiss ion wavelength ranges from 460-500 nm. The process does not alter the transparency, monolithic structure, or surface area of the aerogel. El ectron microscopy and photoelectron spectroscopy reveal no changes bet ween treated and untreated samples. Photoluminescence results from oxy gen defect centers in the aerogel matrix that are observed by Si-29 MA S-NMR as a decrease in the relative amount of Si-(OSi=)(4) sites prese nt in the treated sample. Molecular oxygen strongly quenches the photo luminescence of the treated material. Multiphoton absorbance of infrar ed light also leads to visible light emission. (C) 1997 Elsevier Scien ce B.V.