Lin Bi-Hsuan, Wu Yung-Chi, Chen Huang-Yeh, Tseng Shao-Chin, Wu Jian-Xing, Li Xiao-Yun, Chen Bo-Yi, Lee Chien-Yu, Yin Gung-Chian, Chang Shih-Hung, Tang Mau-Tsu, Hsieh Wen-Feng
Opt Express. 2018 Feb 5;26(3):2731-2739. doi: 10.1364/OE.26.002731.
Polarization-dependent hard X-ray excited optical luminescence (XEOL) was used to study not only the optical properties but also the crystallographic orientations of a non-polar a-plane ZnO wafer. In addition to a positive-edge jump and extra oscillations in the near-band-edge (NBE) XEOL yield, we observed a blue shift of the NBE emission peak that follows the polarization-dependent X-ray absorption near-edge structure (XANES) as the X-ray energy is tuned across the Zn K-edge. This NBE blue shift is caused by the larger X-ray absorption, generating higher free carriers to reduce the exciton-LO phonon coupling, which causes a decrease in the exciton activation energy. The extra oscillations in XANES and XEOL as the polarization is set parallel to the c-axis is attributed to simultaneous excitations of the Zn 4p - O 2pπ -bond along the c-axis and the bilayer σ-bond, whereas only the σ-bond is excited when the polarization is perpendicular to the c-axis. The polarization-dependent XEOL spectra can be used to determine the crystallographic orientations.
偏振相关的硬X射线激发光学发光（XEOL）不仅用于研究非极性a面ZnO晶片的光学性质，还用于研究其晶体取向。除了近带边（NBE）XEOL产率中的正边缘跃变和额外振荡外，我们还观察到，当X射线能量在Zn K边附近调谐时，NBE发射峰的蓝移遵循偏振相关的X射线吸收近边结构（XANES）。这种NBE蓝移是由较大的X射线吸收引起的，产生了更高的自由载流子，从而降低了激子-纵光学声子耦合，导致激子激活能降低。当偏振设置为平行于c轴时，XANES和XEOL中的额外振荡归因于沿c轴的Zn 4p - O 2pπ键和双层σ键的同时激发，而当偏振垂直于c轴时，只有σ键被激发。偏振相关的XEOL光谱可用于确定晶体取向。
