锌磷酸盐玻璃掺杂VO2＋吸收光谱和EPR谱研究

摘要

As an important model system ,3 d1 ions (VO2+ ,V4+ et al) have been extensively investigated by means of electron paramagnetic resonance (EPR) ,and many experimental results of EPR parameters were also measured .The optical absorption and EPR parameters (g factors g‖ ,g⊥ and hyperfine structure constants A‖ ,A⊥ ) of a tetragonal V4+ center in zinc phosphate glass are theoretically investigated ,using the perturbation formulas for a 3 d1 ion in tetragonally compressed octahedra .Since the spin‐orbit coupling parameter ζ0p (≈150 cm -1 ) of ligand O2 - is close to that ζ0d (≈248 cm -1 ) of the central 3 d1 ion in zinc phos‐phate glass doped VO2+ ,the effect of the spin‐orbit coupling parameter ζp0 on the EPR spectra and optical absorption spectra should be taken into account .In this work ,the relationship between the EPR parameters as well as the optical absorption spectra and the local structure of the impurity center are established based on the superposition model .By fitting the calculated EPR pa‐rameters and optical absorption spectra for V 4+ center in zinc phosphate glass to the experimental data ,the local structure pa‐rameters of [VO6 ]8 - cluster are obtained .According to the investigation ,the magnitudes of the metal‐ligand distances parallel and perpendicular to the C4‐axis of [VO6 ]8 - cluster are ,respectively ,R‖ ≈0.175 nm and R⊥ ≈0.197 nm ,the local structure a‐round the V4+ ions possesses a compressed tetragonal distortion along C4 axis .Theoretical results of EPR parameters and optical absorption spectra are in good agreement with experimental data ,the validity of the calculated results has also been discussed . Thus ,perturbation method is effective to the studies the EPR parameters and optical spectra of transition‐metal 3d1 ions in crys‐tals .In addition ,based on the studies of the hyperfine structure constants (A‖ and A⊥ ) ,one can found that the large value of κindicates a large contribution to the hyperfine constant bv the unpaired s‐electron .%3 d1离子（如VO2＋，V4＋）是一类非常重要的离子，其掺杂电子顺磁共振谱已有大量的研究，积累了丰富的实验数据。利用3 d1离子在四角压缩八面体对称中EPR参量的高阶微扰公式，计算了锌磷酸盐玻璃晶体中掺杂VO2＋的EPR参量（g因子g‖，g⊥和超精细结构常数 A‖，A⊥）和光吸收谱。由于锌磷酸盐玻璃晶体中掺杂VO2＋中配体O2－的自旋‐轨道耦合参量ζ0p （≈150 cm －1）与中心过渡金属3 d1离子V4＋的ζ0d （≈248 cm －1）相差不太大，故来自配体的自旋‐轨道耦合参量ζ0p 对EPR参量和光吸收谱的贡献必须予以考虑。采用重叠模型建立了杂质中心结构参数与电子顺磁共振（EPR ）参量以及光吸收谱之间的定量关系；通过拟合锌磷酸盐玻璃中V4＋中心的EPR参量和光吸收谱理论与试验符合，获得了杂质中心[VO6]8－基团的局域结构；研究发现，[VO6]8－基团的平行和垂直于 C4轴的键长分别为：R‖≈0.175 nm ，R⊥≈0.197 nm ，即[VO6]8－基团的局域结构为沿 C4轴方向呈压缩的八面体结构；所得EPR参量和光吸收谱的理论值与实验符合很好，并对上述结果的合理性进行了讨论。这说明微扰法可以用来研究材料中掺杂3d1过渡金属离子的EPR参量和光吸收谱。此外，对超精细结构常数（A‖和 A⊥）的研究发现，较大的芯区极化常数κ值说明VO2＋中未配对的s电子对超精细结构常数有较大的贡献。