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XAFS的择位测量。另一方面，原子分辨率X射线全息术，它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射线全息术的想法。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，并研究了原子分辨率X射线全息的可行性。由于ZnO和蓝宝石都存在XEOL现象，因此本研究采用在Al_2O_3（蓝宝石）单晶上外延ZnO薄膜作为样品。实验在同步辐射装置SPring-8上进行。观察到的XEOL的强度变化对应于Al_2O_3衬底的全息图，这与Zn Kα的X射线荧光全息图不同。为了将 关于我们 XEOL全息图，我们估计的位置和振幅的X-rat驻波线观察到的全息图图案通过平均在一个给定的方向的倒易晶格空间。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。对于轻元素，如Al或Si，由于其内壳电离的小截面和被空气吸收，使用X射线荧光的X射线全息测量通常是困难的。本研究表明，硬X射线全息测量轻元素可以很容易地进行使用XEOL。此外，我们还发现所用的ZnO/Al_2O_3样品在冷却到100 K时，发射出强的紫外光（373 nm），这与ZnO薄膜的禁带宽度相对应。通过光栅单色仪选择ZnO薄膜的发光，可以记录ZnO层的全息图案。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