Faraday Rotations of Divalent Rare-Earth Ions in Fluorides. III

A large rotatory power for ${\mathrm{Eu}}^{2+}$ in cubic fluoride lattices has been observed in the visible range. At frequencies sufficiently removed from the absorption bands, the rotation is proportional to the magnetization. This suggests that the upper levels in the allowed optical transitions are of the $P_J$ character. Measurements on Ca${\mathrm{F}}_2$ and Sr${\mathrm{F}}_2$ crystals doped with very low concentrations of Eu (∼0.005%) also suggest some possible structure for the strong, sharp characteristic line of ${\mathrm{Eu}}^{2+}$ near 4000 Å. The rotatory powers of several other divalent rare-earth ions in fluorides have also been measured.