New photochromic glasses in the system Al-Cd-O-F were obtained. When this type of glass was irradiated by darkening UV light having the wavelength near the absorption edge, a new absorption was induced almost over the whole visible region. The photo-induced absorption decayed very slowly accompanying luminescence, and its half fading time was remarkably shortenedd by heating. Infrared and 27Al MAS-NMR spectra indicated that both AlX4 tetrahedra and AlX6 octahedra (X=O, F) were present and the fraction of octahedra increased with the increasing fluorine content. On the basis of both the ESR spectra and the glass structure model, the color centers were proposed to be oxygen hole centers.
