Gorller-Walrand

Gorller-Walrand, C. and Binnemans, I<. (1996) Rationalization of crystal-field parametrization, in Handbook On the Physics and Chemistry of Rare Earths, vol. 23 (eds K.A. Gschneidner and L. Eyring), Elsevier, Amsterdam. 

Lanthanide complexes with axial symmetry (i.e., possessing at least a threefold axis, see sect. 2.4.2) are exclusively considered because the principal magnetic z axis coincides with the molecular symmetry axis (Forsberg et al., 1995) and the c 2 spherical tensor operators do not contribute to the crystal-field potentials (Gorller-Walrand and Binne-mans, 1996). The rhombic term of Bleaney s approach V6B Hi (eqs. (42), (46)) thus vanishes and the crystal-field independent methods (eqs. (51), (53)) can be used without complications. 

To provide an overview of the rare-earth compounds which have been studied under pressure so far, table 1 lists the compounds, with respect to the doped ion and with the respective references. Obviously, Eu has been studied under pressure in much more host matrices than any of the other elements. This situation is similar to the observations made by Gorller-Walrand and Binnemans (1996), who reviewed the experimental data on spectroscopic properties of trivalent lanthanide ions doped into crystalline host matrices at ambient pressure. They found that Nd and Eu alone built up around 50% of all studies. 

The C are tensor operators, whose matrix elements again can be calculated exactly, whereas the crystal-field parameters Bk are regarded as adjustable parameters. The number of parameters for this potential is greatly reduced by the parity and triangular selection rules and finally by the point symmetry for the f-element ion in the crystal. Detailed information about the crystal-field potential has been given for example by Gorller-Walrand and Binnemans (1996). 

The splitting of free-ion levels by the action of a crystal field depends on the symmetry of the crystal field which in turn reflects the symmetry of the arrangement of the neighboring ions. This property can thus be used to get evidence about the point group symmetry of a site in a given solid once the splitting of the free-ion multiplets have been determined (see, for example, sect. 5.8 of Gorller-Walrand and Binnemans (1996)). This can be a very useful... 

C. Gorller-Walrand and K. Binnemans, Rationalization of crystal-field parameterization 121... 

Gorller-Walrand and Binnemans (1996) have compiled the most complete listing of 4f-electron crystal field parameters across the lanthanide series. However, additional high quality crystal field level measurements for individual ions have been made since 1996 (see, for examples (De Leebeeck et al., 1999), for Nd LiYF4, or (Wegh et al., 2003), for Er LiYF4). 

Driesen, K., Van Deun, R., Gorller-Walrand, C., Binne-mans, K., 2004b. Chem. Mater. 16, 1531. 

Crystal-Field Analysis of Ho3+-LaF3 and Er3+-LaF3 in C2V-Site Symmetry, W.T. Car-nail, G.L. Goodman, R.S. Rana, R Vandevelde, L. Fluyt, and C. Gorller-Walrand, J. Less-Common Met. 116, 17-29 (1986). 

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