Theoretical studies of the optical and EPR spectra for Fe3+ ion in the MF3:Fe3+ (M=Al, Ga) systems

By analyzing the EPR spectra of Fe3+ ion in the fluoride glasses, the local lattice structures around impurity Fe3+ ion in MF3:Fe3+ (M=Al, Ga) systems have been studied by means of diagonalizing the complete energy matrices of the electron-electron repulsion, the ligand-field and the spin-orbit coupling for a d5 configuration ion in a trigonal ligand-field. Both the second-order and fourth-order EPR parameters D and (a-F) are taken simultaneously in the structural investigation. The results indicate that the local lattice structure around octahedral Fe3+ center has an expansion distortion for Fe3+ in MF3:Fe3+ (M=Al, Ga). The expansion distortion may be ascribed to the fact that the radius of Fe3+ ion is larger than that of Al3+ ion and Ga3+ ion, and the Fe3+ ion will push the fluoride ligands upwards and downwards, respectively. The local lattice structure parameters R=1.927 A, θ=55.538o for Fe3+ in AlF3:Fe3+ and R=1.931 A, θ=56.09o for Fe3+ in GaF3:Fe3+ are determined, respectively, and the EPR spectra of the MF3:Fe3+ (M=Al, Ga) systems are satisfactorily explained.