Slater parameters under pressure

An interesting improvement of the SRC model has been discussed by Wang and Bulou (1995). They considered simplified expansion factors used in the Hartree-Fock radial wave-functions for the f-electrons. With these factors it was possible to introduce a k dependence for the pressure-induced change of different Slater parameters. This procedure would remove the weak point of the model which could not account for the observed -dependence of the parameters under pressure. 

Experimental results for the Slater parameter reductions of Nd3+, Pr34-, and U3+ (Troster et al 1995) in LaCl under pressure up to 8 GPa in comparison with results from the dielectric screening model. All values in cm 1 3... 

Similar to the rare-earth trichlorides, also different ternary MYX compounds have been studied thoroughly under high pressure. The results for the pressure-induced changes of the Slater parameter F2 and the spin-orbit coupling parameter of these and other compounds are presented in table 5. Due to the difficulties with the DS model, the evaluation of the parameter shifts has been performed only in terms of the two covalency models. Assuming small changes for the free-ion parameters, the relative changes were approximated by ... 

Usually, it is assumed that pressure effects under the hydrostatic limit are isotropic, which causes a proportional decrease of all distances in the lattice without a change in the local symmetry of the Ln ion. As the result, a standard assumption is that angular factors C (0, (j>) in the crystal-field Hamiltonian are pressure independent and that the only pressure-sensitive parameters are the Slater integrals, spin-orbit coupling, and radial crystal-field parameters (R)- Then, in most cases, pressure causes small linear shifts of the sharp-lines luminescence related to f-f transitions in the Ln " and Ln ions. 

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