在LaAlO3晶体中引入Ce3 +活化剂离子：EPR和NMR研究
Incorporation of the Ce3+ activator ions in LaAlO3 crystals: EPR and NMR study
摘要：
用EPR和NMR研究了Ce ~（3+）掺入LaAlO_3单晶的过程，Ce ~（3+）掺杂量在x= 0.1at.%高达100原子%。从EPR测量，Ce 3 + g张量参数作为Ce浓度的函数。g张量即使在三角相（x <10at.%）也具有正交对称性这表明在La位掺入Ce降低了该离子附近的晶格对称性。通过~（27）Al和~（139）La的高分辨NMR测量进一步研究了La_（1-x）CexAlO_3晶体的局域性质。发现139 La化学位移具有费米接触相互作用的起源。在x = 0.5时，它随Ce浓度线性增加至165 ppm。由于这种强烈的费米接触相互作用，在139 La NMR谱中分辨出对应于不同Ce-O-La自旋转移途径的分离峰。另一方面，在27 Al NMR谱中没有观察到费米接触相互作用。然而，这些光谱包含卫星峰，其强度随Ce浓度的增加而线性增加，而该峰的位置不变。这被解释为与EPR数据一致的Ce离子附近的晶体结构修改的表现。因此，Ce 3+在LaAlO 3中的光学性质将即由该离子附近的局部晶体结构决定。
英文摘要：
This work reports the results of EPR and NMR study of the Ce3+ incorporation in LaAlO3 single crystals grown by the micro-pulling-down method in the range of the Ce concentrations from x=0.1 at.% up to 100 at.%. From EPR measurements, Ce3+ g tensor parameters were obtained as function of Ce concentration. The g tensor has orthorhombic symmetry even in the trigonal phase (x < 10 at.%) suggesting that the incorporation of Ce at La site lowers lattice symmetry near this ion. The local properties of the La1-xCexAlO3 crystals were further studied by 27Al and 139La high-resolution NMR measurements. It was found that 139La chemical shift has the Fermi contact interaction origin. It linearly increases with Ce concentration up to 165 ppm at x = 0.5. Due to this strong Fermi contact interaction, separated peaks corresponding to different Ce-O-La spin transfer passways are resolved in the 139La NMR spectra. On the other hand, no Fermi contact interaction is visible in 27Al NMR spectra. However, these spectra contain satellite peak which intensity linearly increases with increase of Ce concentration leaving position of this peak unchanged. This was interpreted as manifestation of crystal structure modification in vicinity of Ce ions in agreement with EPR data. Thus, optical properties of Ce3+ in LaAlO3 will be namely determined by the local crystal structure near this ion.
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