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The EPR g factors g‖ and g⊥ for Ni3+ ion (created by room‐temperature X‐irradiation of nickel‐doped RbCaF3) in the tetragonal phase of RbCaF3 crystal are calculated from the second‐order perturbation formulas based on a cluster approach for high‐spin 3d7 ions in tetragonal octahedral clusters. The calculated results are in reasonable agreement with the experimental values. The local phase‐transition behavior of the Ni3+ impurity center in RbCaF3 is also estimated from the calculation. It is found that the local phase‐transition behavior in the Ni3+ center is unlike the intrinsic one in the host crystal (in particular, the fluorine octahedra surrounding the cations change from tetragonal compression in the host crystal to tetragonal elongation in the Ni3+ impurity center). The results are discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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The spin-Hamiltonian parameters (g factor g // , g ? and hyperfine structure constants A // , A ? ) for Er 3þ ion at the trigonal Al 3þ site of AlN crystal are calculated by diagonalising the 52 Â 52 energy matrix. The matrix are related to the ground mutiplet 4 I 15/2 and the first to third excited multiplets 4 I 13/2 , 4 I 11/2 and 4 I 9/2 for 4f 11 ions in trigonal crystal field under an external magnetic field. The crystal-field parameters used in the matrix are obtained from the superposition model and the local lattice relaxation due to the substitution of Er 3þ for Al 3þ is considered. The calculated spin-Hamiltonian parameters are in reasonable agreement with the experimental values and the signs of hyperfine structure constants are suggested. The results are discussed.

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