SPIN-HAMILTONIAN PARAMETERS AS A FUNCTION OF PRESSURE-INDUCED AND CATION-INDUCED CHANGES IN NEAREST-NEIGHBOR DISTANCE FOR EUROPIUM-151 IN ALKALINE EARTH FLUORIDES

The electron-paramagnetic-resonance spectra of the systems CaF2: Eu2+151, SrF2: Eu2+151, BaF2: Eu2+151 have been studied at a pressure of 26 kbar. These spectra were interpreted in terms of the usual phenomenological spin Hamiltonian with parameters g (spectroscopic splitting factor), b4 and b6 (crystalline-field parameters), and A (hyperfine splitting factor). The variations of b4 and b6 with pressure were compared with their variations with cation, and a consistent interpretation of the differences was found in terms of local lattice distortions about the impurity europium ions. This model leads to the relationships b4δ-8.8, b6δ-13.6 between the crystalline-field parameters and the nearest-neighbor distance δ. © 1969 The American Physical Society.