In this work, the local structure and the electron paramagnetic resonance (EPR) parameters g factors g// and g?¢???´ and the hyperfine structure constants A// and A?¢???´ of a tetragonal Ni+ center (i.e.,[NiF4]3-cluster) in CaF2 are theoretically investigated, using the high order perturbation formulas of these parameters for a 3d9 ion in tetragonal symmetry (elongated octahedron), in these formulas, the contributions to the spin Hamiltonian parameters from the s-and p-orbitals as well as the spin-orbit coupling coefficient of the ligands are taken into account. On the basis of the studies, the impurity Ni+ is found to locate at the distance of about 0.355 Å from the nearest fluorine plane. The calculated EPR parameters based on the above local structure in this work are in agreement with the experimental data.
