Treatment of silica aerogels with microwave-energized reducing gases induces permanent, visible photoluminescence in the material. The emission wavelength ranges from 460-500 nm. The process does not alter the transparency, monolithic structure, or surface area of the aerogel. Electron microscopy and photoelectron spectroscopy reveal no changes between treated and untreated samples. Photoluminescence results from oxygen defect centers in the aerogel matrix that are observed by 29Si MAS-NMR as a decrease in the relative amount of Si---(OSi[triple bond; length as m-dash])4 sites present in the treated sample. Molecular oxygen strongly quenches the photoluminescence of the treated material. Multiphoton absorbance of infrared light also leads to visible light emission.