Tetragonal Distortion of Structural Defects in Cr~(3+)Doped in Several Perovskites Calculated from the EPR and Optical Data:A Complete Energy Matrix Study

摘要

This paper describes a novel application of a ligand field model in the study of the local molecular structure of the(CrF6)~(3-)coordination complex.Based on the ligand field model,the complete energy matrix which contains the electron-electron repulsion interaction,the ligand field interaction,the spin-orbit coupling interaction,and the Zeeman interaction,has been constructed for a d3 configuration ion in a tetragonal ligand field.In order to study the relation between the EPR,the optical spectra,and the local lattice structures around the centers with tetragonal symmetry in AMF3 codoped with Cr~(3+)and Li~+ions,a three-layer-ligand model is proposed.By diagonalizing the complete energy matrix and employing the three-layer-ligand model,the variational ranges of the local structural parameters around the Cr~(3+)ions are determined,respectively.The results show that the local lattice structures around the Cr~(3+)ions in AMF3 exhibit a compressed distortion,and the magnitude of distorted parameter DLETA R1 of the Cr~(3+)-V_M center is different from that of the Cr~(3+)-Li~+center in AMF3.The compressed distortion is ascribed to the fact that the radius of the Cr~(3+)ion is smaller than those of M~(2+)(M=Cd,Mg,Zn).Moreover,a linear correlation between the difference in the magnitude of distortion parameterAZ? for two different defect centers and the difference in the corresponding values of the zero-field-splitting parameter DLETA D are found first.