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 252 × 252 complete energy matrices for d5 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 ΔE1 and ΔE2 in the ground state 6A1 varying with the structure parameter θ are plotted.