Theoretical study of trigonal Fe3+ center in SrCl2:Fe3+system

The presence of Fe3+ centers with trigonal symmetry in chlorinated SrCl2 crystal is an interesting phenomenon. By diagonalizing the complete energy matrices for a d5 configuration ion in a trigonal ligand-field and simulating the EPR low-symmetry parameters D and (a−F) simultaneously, the local lattice structure around trigonal Fe3+ center in SrCl2:Fe3+ system has been studied. It is shown that Nistor et al.'s viewpoint about replacement is right, but the Cl− ion along 〈111〉 axis around the Fe3+ center is replaced not by an O2− ion but by some negative ion with effective charge to be less than that of Cl− ion. Our results indicate that when the ratio of the effective charge of the negative ion to that of Cl− ion is 0.8 as well as the distortion angle of the upper triangle is Δθ=−4.682°, the EPR parameters D and (a−F) can be explained satisfactorily.