The electronic structure and optical property of heterostructural TiO 2 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 TiO 2 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 "bulk" pristine TiO 2 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 TiO 2 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 TiO 2 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 TiO 2 phase, respectively.The relationship between the observed luminescence intensity ratio and the phase content ratio of rutile and sodium titanate is discussed.
Pressure-induced transformations of anatase TiO2 nanotubes probed by in situ Raman spectroscopy and synchrotron X-ray diffraction reveal novel compression behaviors.
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