ERR of Off-Center Eu²⁺ Ions with Resolved Structures in RbCl

Abstract

In RbCl: Eu²⁺ crystals, there are found three groups of EPR spectra with an intensity ratio of 2:1:1, which are attributed to off-center displacements of Eu²⁺ ions along [111] axis from normal lattice sites.
The spectra of the off-center Eu²⁺ ions can be described by combining the spin Hamiltonian in an orthorhombic field and the perturbation terms depending on the magnetic field as follows; (Remark: Graphics omitted.), where g=1.995, b₂⁰=294.6, b₂²=−139.8, A¹⁵¹=−31.3, u=−0.2∼0.9, U=0∼−0.05 (10⁻⁴ cm⁻¹) at room temperature. The displacement is estimated from the angles between the principal axes and [110] directions to be 0.082a (a: anion to cation distance), and the induced dipole moment to be 2.57 Debye. Thermal stabilities of the off-centers are discussed in the temperature range between room temperature and 150°C.