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 α 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 superposition 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. Meanwhile, we obtain that a ligand F^- along the [001]-axis moves towards the central Fe³⁺ ion by Δ = 0.0020 nm in RbCdF₃ and 0.0028 nm in CsCdF₃. These results are quite different from Δ = 0.0104 nm and Δ = 0.0112 nm, respectively, obtained in previous work by using the superposition model of spin-Hamiltonian and ignoring the effect of the vacancy.