Optical properties of cobalt-doped zinc aluminosilicate transparent glass ceramics in the visible – near-infrared (IR) spectral range have been studied. It was shown that the absorption and luminescence properties of these glass ceramics are defined mainly by tetrahedrally coordinated Co2+ ions located in ZnAl2O4 gahnite nanocrystals formed in the glass ceramic matrix. The luminescence in the visible and near IR was assigned to the transitions from the 4T1(4P) to the 4A2 and 4T2 energy levels of tetrahedrally coordinated Co2+ ion. Absorption saturation and bleaching relaxation under excitation of the 4A2→4T1(4F) transition were studied. Luminescence decay and bleaching relaxation times lie in the ranges 25–200 and 500–800 ns, respectively, depending on the Co concentration. The value of the ground-state absorption cross section of tetrahedrally coordinated Co2+ ions in zinc aluminosilicate transparent glass ceramics was estimated to be 2.0×10-19 cm2 at the wavelength of 1.54 μm. © 2003 American Institute of Physics.