Dopant location identification inNd3+-dopedTiO2nanoparticles

Abstract

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 $(0\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}1.5\phantom{\rule{0.3em}{0ex}}\mathrm{at.}\phantom{\rule{0.3em}{0ex}}%)$ dopant location and the structural changes associated with the doping in anatase $\mathrm{Ti}{\mathrm{O}}_{2}$ nanoparticles, which were synthesized by metalorganic chemical vapor deposition. Nd ions were determined to have a trivalent chemical state and substitute for ${\mathrm{Ti}}^{4+}$ in the $\mathrm{Ti}{\mathrm{O}}_{2}$ structure. The substitutional ${\mathrm{Nd}}^{3+}$ ions cause anatase lattice expansion along $c$ direction with a maximum value of $0.15\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ at 1.5 % Nd doping level and the local structure of the dopants changes towards rutile like configuration. The lengths of the nearest neighbor $\mathrm{Nd}\text{\ensuremath{-}}\mathrm{O}$ and $\mathrm{Nd}\text{\ensuremath{-}}\mathrm{Ti}$ bonds increase by $0.5--0.8\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ compared to their counterparts in the pure $\mathrm{Ti}{\mathrm{O}}_{2}$ host structure. The substitutional nature of ${\mathrm{Nd}}^{3+}$ dopants explains why they are efficient not only for charge carrier separation but also for visible light absorption in $\mathrm{Ti}{\mathrm{O}}_{2}$.