Nanoscale Clarification of the Electronic Structure and Optical Properties of TiO2 Nanowire with an Impurity Phase upon Sodium Intercalation

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• 作者：Jun Li ; Zhiqiang Wang ; Ankang Zhao ; Jian Wang ; Yang Song ; Tsun-Kong Sham
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：August 6, 2015
• 年：2015
• 卷：119
• 期：31
• 页码：17848-17856
• 全文大小：498K
• ISSN：1932-7455

文摘

The electronic structure and optical property of heterostructural TiO₂ nanowire (NW) synthesized by a hydrothermal process have been extensively studied. X-ray diffraction (XRD) and X-ray absorption near-edge structure (XANES) were used to probe the crystal structure and the local structure and bonding (unoccupied electronic states) of the as-obtained TiO₂ NW, respectively. Discrepancy between XRD and XANES results without spatial resolution was observed and interpreted on the basis of the inhomogeneous distribution of a sodium titanate impurity phase among the 鈥渂ulk鈥?pristine TiO₂ phase. Scanning transmission X-ray microscopy (STXM), on the other hand, provides nanoscale clarification for the divergence with a spatial resolution of 30 nm. Using STXM, the nature of the sodium titanate impurity phase and pristine TiO₂ phase was thoroughly characterized by comparing the XANES at the Na K-edge, Ti L_3,2-edge, and O K-edge. The local effect of sodium intercalation into the TiO₂ matrix together with the presence of sodium titanate impurity to the electronic structure of the entire NW specimen was addressed. Analysis was also conducted using 2D XANES-XEOL (X-ray excited optical luminescence) spectroscopy. The optical interplay with structural properties reveals the element and site specificity of the observed luminescence. Of these, the dominant green emission and minor near-infrared (NIR) luminescence were attributed to the defect states from both Ti and O sites within the minor sodium titanate phase and the dominant rutile TiO₂ phase, respectively. The relationship between the observed luminescence intensity ratio and the phase content ratio of rutile and sodium titanate is discussed.