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By diagonalizing a set of complete energy matrices constructed for a d(5) configuration ion in a trigonal ligand field, a reasonable interpretation is obtained for the EPR zero-field splitting of Mn2+ ions located at octahedral sites in yttrium aluminum garnet. It is shown that the local lattice structure around an octahedrally coordinated Mn2+ center has an expansion distortion, which may be attributed to the fact that the radius of Mn2+ ion is larger than that of Al3+ ion, and the Mn2+ ion will push the oxygen ligands outwards. Simultaneously, the local lattice structure distortion parameters Delta R = 0.1825-0.2158 A and Delta theta = 1.220 degrees-1.315 degrees for the octahedral Mn2+ center in the crystal are determined, respectively. Meanwhile, we also demonstrated that the empirical impurity-ligand distance R approximate to R-H + 1/2(r(i)-r(h)) is not suitable for the YAG:Mn2+ system which has been approximately taken in previous works. (c) 2006 Elsevier Ltd. All rights reserved.