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

► The complete energy matrix is used in the studies of EPR spectra for the Er3+ ion. ► Three Er3+ centers in ThO2 are well explained by obtained local distortion parameter. ► The dependence of EPR g-factors on the distortion parameter is characterized. ► The deviation of average g-tensor gav from the cubic gc value is explained.