Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu, PR China.
Spectrochim Acta A Mol Biomol Spectrosc. 2011 Jun;79(1):82-6. doi: 10.1016/j.saa.2011.02.006. Epub 2011 Mar 1.
The electron paramagnetic resonance (EPR) parameters (g factor, the hyperfine structure constant A and the superhyperfine parameters A' and B') for Mn(2+) in the fluoroperovskites ABF(3) (A=K and Cs; B=Zn, Mg, Cd and Ca) are theoretically investigated from the perturbation formulas of these parameters for a 3d(5) ion under ideal octahedra. In the above treatments, not only the crystal-field mechanism but also the charge transfer mechanism is considered uniformly on the basis of the cluster approach. The theoretical EPR parameters are in good agreement with the experimental data. The charge transfer contribution to the g-shift Δg (≈g-g(s), where g(s)≈2.0023 is the spin-only value) is opposite (positive) in sign and comparable in magnitude to the crystal-field one. Nevertheless, the charge transfer contribution to the hyperfine structure constant shows the same sign and about 10% that of the crystal-field one. So, the conventional argument that the charge transfer contributions to the zero-field splittings are negligible for 3d(5) ions under low symmetrically distorted fluorine octahedra is proved no longer valid for the Δg analysis of ABF(3):Mn(2+) in view of the dominant second-order charge transfer perturbation terms. The unpaired spin densities of the fluorine 2s, 2p σ and 2p π orbitals are determined from the quantitative dependences upon the related molecular orbital coefficients, rather than obtained by fitting the observed superhyperfine parameters in the previous works.
电子顺磁共振（EPR）参数（g 因子、超精细结构常数 A 以及超精细参数 A'和 B'）对于氟代钙钛矿 ABF(3)（A=K 和 Cs；B=Zn、Mg、Cd 和 Ca）中的 Mn(2+)离子进行了理论研究，这些参数是通过 3d(5)离子在理想八面体中的微扰公式得出的。在上述处理中，不仅考虑了晶体场机制，还基于团簇方法统一考虑了电荷转移机制。理论 EPR 参数与实验数据吻合良好。与晶体场相比，电荷转移对 g 位移 Δg（≈g-g(s)，其中 g(s)≈2.0023 是自旋仅有的值）的贡献具有相反（正）的符号且在大小上相当。然而，电荷转移对超精细结构常数的贡献具有相同的符号，约为晶体场的 10%。因此，对于低对称畸变氟八面体中的 3d(5)离子，传统观点认为电荷转移对零场分裂的贡献可以忽略不计，这一观点在 ABF(3):Mn(2+)的 Δg 分析中不再有效，因为二阶电荷转移微扰项占据主导地位。未配对的氟 2s、2p σ 和 2p π 轨道的自旋密度是通过与相关分子轨道系数的定量关系来确定的，而不是通过拟合以前工作中观察到的超精细参数来获得的。
