ELECTRON-SPIN-RESONANCE SPECTRUM OF DIVALENT EUROPIUM IN THORIUM DIOXIDE

Either 2-MeV electron or Co60 γ irradiation was employed to reduce trivalent Eu in ThO2 to the divalent state. The ESR spectrum of the Eu2+ ions could only be observed at temperatures below 77°K and posessed trigonal symmetry about the four 111 axes. The axial crystal field was so strong that only the |MJ=12 to |MJ=-12 transition was observed with a highly anisotropic g value (gII=1.9678±0.0005 and g=7.867±0.002). Hyperfine structure was resolved but the angular variation was complex because of a nuclear quadrupole interaction that was of the same order of magnitude as the hyperfine interaction. Spin-Hamiltonian constants which describe the ESR spectrum were determined with the use of a computer. Electron irradiation at 77°K was not successful in producing Eu2+ in isomorphous CeO2. In addition, crystals of ThO2 and CeO2 doped with trivalent thulium were also electron-irradiated at 77°K, but no change in the Tm valence was detected. © 1969 The American Physical Society.