[en] Co ions were implanted into colorless and transparent synthetic sapphires with doses of 5x10¹⁶-5x10¹⁷ ions/cm² at an energy of 20 keV. The optical absorption spectrum and the XPS (X-ray photoelectron spectroscopy) spectrum were measured for as-implanted and annealed samples up to 1200degC in sequence. Although an as-implanted sample showed only dark grey, on heating the sample its color tone was gradually changed. The color turned green when it was heated at 800degC for 3 h. Light blue color was obtained by heating the sample at 1000degC for 3 h. XPS spectra of Co 2p_3/2 implanted into sapphire was changed when it was heated at 800 or 1000degC. Although the spectra for the as-implanted sample almost coincided with that of pure metal, the spectrum for the annealed samples showed two peaks, one near the metallic state and the other at a distance of about 3 eV in the binding energy, which indicates the existence of two types of electronic configurations of Co with different binding energies in the colored sapphire. (orig.)