EN
A theoretical description of shallow donor absorption spectra in CdF_{2} in the infrared region is given. The properties of the stable (Y) and bistable (In) donors are analyzed and quantatively described. It is shown that the bistability of donors and the shape of the infrared absorption band have the same origin, which is the combined effect of electron-LO-phonon coupling, conduction band non-parabolicity and short-range central-cell potential.