Abstract Optical absorption spectra over the range 0.2 to 15 μ, and electrical resistivity and Hall coefficient values, have been measured over a broad temperature range in crystals of CdF 2 containing In or Eu centers. The observed optical and transport properties suggest that these impurities, at low temperatures, trap electrons in atomic states. As the temperature increases, however, both In and Eu can also provide hydrogenic effective mass states for electrons. The observed i.r. absorption is attributed primarily to transitions from these latter states into the conduction band.