Lattice Distortion and Cd~(2+) Vacancy for CsCdF_3:Cr~(3+) Crystals

The quantificational relationship between EPR zero-field splitting parameter D and structure parameters of Cr~(3+) vacancy centre in CsCdF_3: Cr~(3+) crystals was established according to the superposition model and third-order perturbation theory. The existence of Cd~(2+) vacancy and the lattice distortion were verified. Meanwhile, F~- ion moving toward the central Cr~(3+) ion by X_1=0.00291nm, X_2=0.001nm, X_3=0.00262nm was obtained. Good agreement between the theoretical results and the experimental values shows that the assumption of the Cd~(2+) vacancy and the lattice distortion is reasonable. Although the main of source of the tetragonal crystal field comes from the Cd~(2+) vacancy caused by the charge compensation, the contribution of the lattice distortion can not be neglected.