EPR investigations on the hole centres in CaWO 4 at T = 4.2 K

EPR investigations at T = 4.2 K show the principal g ‐values of the radiation induced hole centres in CaWO 4 being different from those obtained at temperatures ≧ 78 K, whereas the principal directions of the g ‐tensor remain nearly unchanged. The g ‐tensor at T = 4.2 K is quite well explained by a model in which the hole is assumed in an oxygen P π ‐orbital, including some admixtures from other orbitals of the WO 4 tetrahedron. In this model, combined with a weak bonding between two neighboured WO 4 tetrahedra, the observed hyperfine interaction of the hole with two inequivalent W 183 nuclei can be understood too. The transition to the results at higher temperatures is possible by a faster exchange of the hole between the two WO 4 complexes.