The dependence of EPR g-factors on the local structure for tetragonal Nd3+and Er3+centers in CaF2 crystals

The dependence of EPR g-factors on structure parameter for tetragonal Nd3+/Er3+ centers in CaF2 crystals was studied by diagonalizing the 364 x 364 complete energy matrices. Our studies indicate that the central rare-earth ion in the tetragonal (ReF8)5-(Re = Nd and Er) cluster will undergo an off-centre displacement toward the interstitial F- ion, and the upper four adjacent ligands may suffer an opposite displacement along C4 axis. Based on the present model, the local lattice distortions for both of the centers were evaluated, respectively. The large differences of the anisotropy of g-factors can be interpreted reasonably, though similar structure distortions were expected for the tetragonal Nd3+/Er3+ centers in CaF2 crystals. Moreover, the high-order mixing effects on the EPR g-factors were evaluated by using the wavefunctions of lowest Kramers states.