-The location of the energy levels of rare-earth ( RE ) elements in the energy band diagram of BaF 2 and CdF 2 crystals is determined. The role of RE 3+ and RE 2+ ions in the capture of charge carriers, luminescence, and the formation of radiation defects is evaluated. It is shown that the substantial difference in the luminescence properties of BaF 2 : RE and CdF 2 : RE is associated with the location of the excited energy levels in the band diagram of the crystals.