EPR and ENDOR of BaF₂:Tm²⁺under uniaxial stress

The Orbit?Lattice Interaction for Lanthanide Ions. II. Strain and Relaxation Time Predictions for Cubic Systems

“…The results of Baker and Currell (1976) are of particular relevance to our present discussion because they were employed by Baker et al (1977) to test the superposition model. Their technique was first to determine the V(r j, k) from the experimental data and then to use least squares fitting to obtain the appropriate superposition model parameters.…”

“…Orbach and Blume 1962; Baker and van Ormondt 1974) to express the dynamic coupling between lattice vibrations and the open shell electrons of a paramagnetic ion as a coupling between strains in a continuous medium (representing the lattice) and corresponding changes in the crystal field parameters. Such a model is appropriate for the coupling to long wave (acoustic) phonons and to static (or slowly oscillating) applied stresses.…”

“…Buisson and Borg (1970) parameters. This table is adapted from Table A2 of Baker and van Ormondt (1974), Table 1 of Baker et al (1977) and Table 1 A considerable amount of work has been carried out to determine the parameters in spin-lattice Hamiltonians by using electron paramagnetic resonance (EPR) results for strained crystals. This approach has the advantage that it avoids the problems associated with providing an adequate characterization of the phonon spectrum.…”

“…The problems involved in carrying out such a determination are well exemplified by the extremely careful work of Baker and Currell (1976). They studied the EPR of Er3+ : MgO and Dy3 + : CaF 2 under uniaxial stress, measuring a sufficient number of splittings to determine the spin-lattice parameters to (typically) 5 %.…”

“…In recent years a considerable amount of data has become available relating to the dynamic crystal field in cubic crystals, and some of this has recently been used to test the usefulness of the superposition model by , North andStapleton (1977a, 1977b) and Baker et al (1977), as well as an alternative electrostatic model due to Buisson and Borg (1970). These papers came to rather definite conclusions about the inadequacy of the superposition model as a means of predicting values of the dynamic parameters, although the reasons for this apparent failure were unexplained.…”