In the present work we used Hartree-Fock-Slater local-density discrete
variational method to calculate the energy level of some rare earth d
oped BaF2 crystals and proposed that the Eu, Dy and Yb elements will c
hange their valence from +3 to +2 under irradiation and thus change th
e optical properties of the crystals. The results show that this radia
tion effect model is in good agreement with experiments.