Theoretical study on local defect structure of (FeO4)(5-) clusters in YGG and LGG crystals.

The optical spectrum and the local defect structure of tetrahedral (FeO4)(5-) clusters are investigated in yttrium gallium garnet (YGG) and lutetium gallium garnet (LGG) crystals by means of the 252x252 complete energy matrices for d(5) configuration ions in tetragonal ligand field. The results show that the local defect structures around tetrahedral Fe3+ centers display an expansion effect. Simultaneously, the (FeO4(5-) clusters in the two different crystals have very similar local structures, which are close to those in YIG garnet crystal. Finally the relative curves of the zero-field splitting energies DeltaE1 and DeltaE2 in the ground state (6)A(1) varying with the structure parameter theta are plotted.