AN INVESTIGATION FOR THE Cd²⁺-VACANCIES IN RbCdF₃ and CsCdF₃ CRYSTALS DOPED WITH Fe³⁺ IMPURITIES

This paper presents high-order perturbation calculations for the zero-field splitting parameters D, F, and a of Fe³⁺-V_Cd pairs in RbCdF₃ and CsCdF₃ crystals doped with Fe³⁺ impurities. In comparison with experimental data, the present results are better than those obtained in previous work by using the phenomenological su-perposition model of spin-Hamiltonian. Moreover, the crystal fields arising from the Cd²⁺-vacancy and their induced crystal lattice distortion are analysed and calculated. It is found that the contribution from the Cd²⁺-vacancies cannot be ignored. Mena-while, we obtain that a ligand F^- along the 001-axis moves towards the central Fe³⁺ ion by \Delta= 0.0020nm in RbCdF₃ and 0.0028nm in CsCdF₃. These results are quite different from \Delta = 0.0104nm and \Delta = 0.0112nm, respectively, obtained in previous work by using the superposition model of spin-Hamiltonian and ignoring the effect of the vacancy.