Studies of the defect structures of the trigonal Cr3+-VC centers in fluoroperovskites from EPR and optical spectra

The EPR parameters (zero-field splitting D and g factors g(vertical bar vertical bar), g(perpendicular to)) and the first excited state splitting Delta(E-2) of the trigonal Cr3+-Vc centers (Vc denotes the cation vacancy in a C-3 axis) in Cr3+-doped fluoroperovskites KMgF3, KZnF3, CsCdF3, CsCaF3, RbCdF3 and BaLiF3 are studied from the high-order perturbation formulas. From the studies, the defect structures (characterized by the vacancy-induced displacements Delta(x1) of Cr3+ ion and Delta x(2) of the three F- ion between Cr3+ and Vc) of these trigonal Cr3+-Vc centers are determined. It is found that the signs of displacements Delta x(1) and Delta x(2) are consistent with the expectations based on the electrostatic interactions, and the magnitudes of Delta x(1) and Delta x(2) for Cr3+ in the inverse perovskite BaLiF3 are larger than those for Cr3+ in the classical perovskites. The results are discussed. (c) 2005 Elsevier B.V. All rights reserved.