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

Electron paramagnetic resonance, electron-nuclear double resonance, and opt ical spectroscopy of the tetragonal Yb3+ center in KMgF3 are reported here. The results of these experiments allow us to conclude that a previously gi ven structural model as well as the interpretation of the optical spectrum of this center are incorrect. A model is presented and experimentally and t heoretically justified. In particular, the values of the hyperfine and tran sferred hyperfine interaction parameters were determined as well as an expe riment-based energy-level scheme. Its parametrization is performed by inclu ding simultaneously the crystal field and the spin-orbit interaction within the F-7 term. Furthermore, a theoretical analysis of the transferred hyper fine interaction (THFl) parameters is presented. It is further shown from o ptics and from microscopic calculations of the THFI parameters that g(paral lel to) and g(perpendicular to), have opposite signs and that the rule of c orrespondence 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-s ymmetry crystal field acting on the rare-earth ion.