The EPR spectra of octahedral Fe3+ center in lutetium aluminum garnet have been studied by means of the complete energy matrices for a d(5) configuration ion in a trigonal ligand-field. It is manifested that the local lattice structure around an octahedrally coordinated F3+ e center has an expansion distortion from that of undistorted host Al3+ ion. The expansion distortion can be ascribed to the fact that the radius of Fe3+ ion is bigger than that of Al3+ ion, and consequently the Fe3+ ion pushes the oxygen ligands outwards. Simultaneously, for the octahedral Fe3+ center in the crystal, the local lattice structure parameters, R = (2.007 +/- 0.022) A and theta = (52.708 +/- 0.032)degrees, which reflect the interactions between impurity and crystal lattice, are determined from our calculation, and EPR parameters a, D, and (a - F) also get a unified explanation. (c) 2005 Elsevier B.V. All rights reserved.