Orbit-lattice interaction in Γ8quartets. II. A rigorous test for various models of the interaction for Er3+:MgO and Dy3+:CaF2

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Abstract
For pt.I see ibid., vol.9, p.3819 (1976). The authors discuss the experimental results on the effect of uniaxial stress on the EPR of the Gamma 8 ground states. Baker and Currell (in pt.I) used the data to calculate eight of the nine unknown parameters of the orbit-lattice Hamiltonian HOL. Such a large number of parameters can be measured only for the few systems which exhibit EPR in a Gamma 8 state. Hence, to make quantitative calculations involving HOL it is imperative to be able to express HOL in terms of fewer parameters. The data of Baker and Currell have been used to make a rigorous test of two models for reducing the number of independent parameters of HOL: (1) the generalised electrostatic model of Buisson and Borg (1970) and (2) the superposition model of Newman (1971). These models have also been modified to relax the relationship between HOL and the static crystal field, and to make allowance for local variations of elastic constants and other local ionic displacements. Within the context of a pure LS coupling approximation for the two ions, neither the simple nor the modified form of either model is adequate to describe HOL.
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