Understanding of optical luminescence mechanism of phosphors by establishment of X-ray luminescence holography

X射线激发光致发光(XEOL)已被应用于位选择性XAFS测量。另一方面，原子分辨率x射线全息术可以确定特定原子周围的局部结构，通常使用x射线荧光。在开始这个项目之前，还没有将XEOL用于其他X射线全息摄影的想法。为了探索XEOL应用的新的分析可能性，我们重点研究了XEOL强度的X射线入射光束角各向异性，并研究了原子分辨X射线全息术的可行性。本研究采用Al_2O_3(蓝宝石)单晶上的氧化锌外延薄膜作为样品，因为已知在氧化锌和蓝宝石上都存在XEOL。这些实验是在同步辐射设施Spring8进行的。观察到的XEOL的强度变化与Al_2O_3衬底的全息图相对应，而不同于Zn-K-α的X射线荧光全息图。为了将…属性在XEOL全息图的基础上，我们通过在倒易晶格空间的给定方向上取平均值来估计在全息图图案中观察到的X-RAT驻波线的位置和幅度。对ZnO/Al_2O_3的XEOL光谱的测量表明，蓝宝石的发光占主导地位，这与XEOL全息图的结果一致。由于Al、Si等轻元素的内壳层电离截面较小，且易被空气吸收，因此利用X射线荧光进行X射线全息测量具有一定的难度。本研究表明，利用XEOL可以很容易地实现对轻元素的硬X射线全息测量。此外，我们还发现，我们所用的ZnO/Al_2O_3样品在冷却到100K时发出了与氧化锌薄膜的带隙相对应的强紫外光(373 Nm)，通过使用光栅单色仪选择来自氧化锌薄膜的发光，可以记录到氧化锌薄膜的全息图。较少

X-ray excited optical luminescence (XEOL) has been applied to the site selective XAFS measurements. On the other hand, atomic resolution x-ray holography, which can determine local structure around a specified atom, normally uses the x-ray fluorescence. Before starting this project, there has been no idea of the use of XEOL for othe X-ray holography. To explore new analytical possibility of the XEOL application, we focused on X-ray incident beam angular anisotropy of the XEOL intensity and studied a feasibility of atomic resolution X-ray holography. A ZnO epitaxial film on Al_2O_3 (sapphire) single crystal was adopted for the sample in the present study, because the XEOL is known to be occurred for ZnO and sapphire. The experiments were done at the synchrotron radiation facility SPring-8. The observed intensity variation of the XEOL corresponded to the hologram pattern of Al_2O_3 substrate, which was different from the X-ray fluorescence hologram pattern of Zn Kα. In order to attribute … More the XEOL hologram, we estimated positions and amplitudes of the X-rat standing wave lines observed in the hologram patterns by averaging over a given direction of reciprocal lattice space. Measurement of the XEOL spectrum from the ZnO/Al_2O_3 showed that the luminescence from sapphire was dominant, and this was consistent with the result of the XEOL hologram. The X-ray holography measurement using x-ray fluorescence is generally difficult for light elements, such as Al or Si, because of its low cross section for inner shell ionization and the absorption by air. The present study demonstrates that hard x-ray holography measurement for light element can be easily carried out using XEOL. Moreover, we found that the ZnO/AL_2O_3 sample used here emit the strong ultraviolet luminescence (373 nm), which corresponded to bang gap of ZnO thin film, by cooling to 100 K. By selecting the luminescence from ZnO thin film using a grating monochromator, the hologram pattern of ZnO layer could be recorded. Less