Monoclinic and orthorhombic standardization of spin-Hamiltonian parameters for rare-earth centers in various crystals

In a previous paper the standardization of the spin-Hamiltonian (SH) parameters for transition-metal ions at orthorhombic symmetry sites was dealt with using the computer package CST. In this paper the non-standard SH parameters for rare-earth ions at monoclinic and orthorhombic symmetry sites in various crystals, identified in an extensive literature survey, have been unified and standardized. The original non-standard zero-field splitting (ZFS) parameter sets given in various (i) parameter and operator notations, (ii) units and (iii) conventions for the axis systems are converted and presented in a unified way. Both the monoclinic- and orthorhombic-type standardization provided by the CST package have been employed. All the standardized ZFS parameters are expressed in the extended Stevens' (ES) notation b(k)(q) and in units of 10(-4) cm(-1). The transformations S-i required and the ratio lambda' = B-2(2)/B-2(0) = b(2)(2)/b(2)(0) and lambda = E/D are also provided in the tables. Implications of the standardization for the axis system used and interpretation of the EPR results are discussed, thus revealing several inconsistencies in the original papers. It is concluded that the results presented may facilitate future determination of the ZFS parameters by EPR and increase the reliability of data. (C) 2000 Elsevier Science B.V. All rights reserved.