Theoretical studies of EPR spectra and defect structure for three Er3+ centers in thorium dioxide

The EPR parameters of three nonequivalent Er3+ centers in ThO2 have been reasonably explained by diagonalizing complete energy matrices. The results indicate that the center III may be attributed to a positive charge compensator located at the [1 1 1] axis of cube, and the nearest ligand close to the compensator has a displacement away from central ion by about 0.19 Å. As for the center II, it is expected that the four ligand ions close to the compensator have a displacement by about 0.046 Å along the [1 0 0] direction. Moreover, the dependence of EPR g-factors on shift parameter ΔZ is discussed.