Dopant location identification in Nd3+-doped TiO2 nanoparticles

Large band gap semiconductors are typically doped in order to enhance their photocatalytic, photovoltaic, and other chemical and optoelectronic properties. The identification of dopant position and its local environment are essential to explore the effect of doping. X ray techniques, including extended x ray absorption fine structure, x ray photoelectron spectroscopy, and x ray diffraction, were performed to analyze the Nd (0to1.5at.%) dopant location and the structural changes associated with the doping in anatase TiO2 nanoparticles, which were synthesized by metalorganic chemical vapor deposition. Nd ions were determined to have a trivalent chemical state and substitute for Ti4+ in the TiO2 structure. The substitutional Nd3+ ions cause anatase lattice expansion along c direction with a maximum value of 0.15Å at 1.5% Nd doping level and the local structure of the dopants changes towards rutile like configuration. The lengths of the nearest neighbor Nd-O and Nd-Ti bonds increase by 0.5-0.8Å compared to their counterparts in the pure TiO2 host structure. The substitutional nature of Nd3+ dopants explains why they are efficient not only for charge carrier separation but also for visible light absorption in TiO2.