The relationships between the crystal structure parameters, the zero-field splitting parameter D, the g-factor components (g||,g), and the splitting δ(2E) of the 2E(3d3) state for the double-doped Cr3+:Mg2+:LiNbO3 system were investigated by using the superposition model and a complete diagonalization procedure within the 3d3 configuration. To study the effect of disorder in the local lattice distortions on the experimentally measured parameters, two possible local structure models were considered. Model I assumes variation of the position of O2- ions around the Cr3+ defect ion, whereas model II assumes the displacement of Cr3+ ion from the original Nb5+ position towards a more centered position in the O octahedron. The detailed analysis suggested that model I describes reasonably the properties of the new Cr3+ defect center in the Cr3+:Mg2+:LiNbO3 system. The very small value of D, the isotropic g-factor, and the large value of δ(2E) observed in this system were successfully interpreted. The calculations indicated that the three O2- ions above the Cr3+ rotate by 1.87° towards the [111]-axis, while the three O2- ions below the Cr3+ rotate by 0.31° towards the [111]-axis. Hence, the disorder effects play an important role in explaining the spectroscopic properties of Cr3+ ions in Cr3+:Mg2+:LiNbO3.

The Effect of Disorder in the Local Lattice Distortions on the EPR and Optical Spectroscopy Parameters for a New Cr3+ Defect Center in Cr3+:Mg2+:LiNbO3. Z.Y.Yang, C.Rudowicz, J.Qin: Physica B, 2002, 318[2-3], 188-97