EPR, ENDOR, and optical spectroscopy of the tetragonal Yb3+ center in KMgF3

Electron paramagnetic resonance, electron-nuclear double resonance, and optical spectroscopy of the tetragonal Yb3+ center in KMgF3 are reported here. The results of these experiments allow us to conclude that a previously given structural model as well as the interpretation of the optical spectrum of this center are incorrect. A model is presented and experimentally and theoretically justified. In particular, the values of the hyperfine and transferred hyperfine interaction parameters were determined as well as an experiment-based energy-level scheme. Its parametrization is performed by including simultaneously the crystal field and the spin-orbit interaction within the F-7 term. Furthermore, a theoretical analysis of the transferred hyperfine interaction (THFl) parameters is presented. It is further shown from optics and from microscopic calculations of the THFI parameters that g(parallel to) and g(perpendicular to), have opposite signs and that the rule of correspondence between the cubic g factor and (g) over tilde = 1/3(g(x) + g(y) + g(z)) does not depend on the relative magnitude of the cubic and low-symmetry crystal field acting on the rare-earth ion.