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(parallel), g(perpendicular)) and the first excited state splitting Delta(2E) of the trigonal Cr3+-Vc centers (Vc denotes the cation vacancy in a C3 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 x2 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 x1 and Delta x2 are consistent with the expectations based on the electrostatic interactions, and the magnitudes of Delta x1 and Delta x2 for Cr3+ in the inverse perovskite BaLiF3 are larger than those for Cr3+ in the classical perovskites. The results are discussed.