Spectroscopic properties of recently discovered fluorescent sapphire single crystals (Al2O3:C,Mg), developed for volumetric optical data storage, are investigated. Polarized optical absorption, excitation-emission spectra, and quantum yield of fluorescence of the crystal in two different photochromic states are studied. The spatial distribution of intensity and polarization ratio of the fluorescence associated with the 435/520- and 620/750-nm excitation-emission bands, characteristic of the two photochromic states of the crystal, display strong anisotropy. The intensity distribution, and hence the spatially averaged quantum yield of fluorescence for the two states, measured relative to standard laser dyes are similar for different crystallographic orientations. The average quantum yield is found to be close to unity for both the states. The anisotropic properties of optical absorption and fluorescence suggest a model of double oxygen vacancy.