5. Concluding remarks

TiO2 NT is a versatile material. It could be directly used in batteries, photocatalysis, solar cells on their own, and it can also serve as substrate for further decorating of nanoparticles or bioactive compounds. Understanding the electronic structure of TiO2 NT-based materials and controlling their electronic and optical properties is hence crucial for integrating them into practical application. Both anatase and rutile nanostructures have their characteristic luminescence at visible green and near IR regions, respectively. The visible green luminescence in NT is of a surface origin, and it is highly sensitive to surface defect and surface modification. Near IR emission, on the other hand, is of bulk origin of rutile. It is independent of material morphology and always appears as long as rutile phase is present, even in a mixed structure. Thus XEOL in combination with XANES is a unique and powerful technique which tracks the relationship of the observed luminescence and the specific local chemical structure that is responsible for it. It is hence useful in analyzing the luminescence origin of novel TiO2 nanostructures and related materials.
