Paramagnetic Resonance Study of Irradiated Single Crystals of Calcium Tungstate

Gamma irradiation of calcium tungstate at 77°K produces two paramagnetic species in high yield. Measurements of yields and of rates of disappearance upon warming indicate the two species are formed and disappear upon warming in one to one correspondence. The principal axis directions and g tensors have been measured and indicate that one species contains a surplus electron while the other is electron-deficient (hole). Hyperfine effects of W183 have been observed. The electron-deficient species contains two tungsten atoms with small isotropic hyperfine interactions. Its unpaired electron must be highly localized in orbitals of atoms other than tungsten. The electron-surplus species contains one tungsten atom with an anisotropic hyperfine interaction. This center could be WO43—, but from the lack of symmetry of the measured g values it must be formed near a lattice defect. Experiments with heat-treated crystals indicate lattice defects to be important in the radiation effect.