Non-uniform distribution of dopant iron ions in TiO2 nanocrystals probed by X-ray diffraction, Raman scattering, photoluminescence and photocatalysis

摘要

We have analyzed the experimental XRD patterns and micro-Raman spectra of iron doped nanocrystals of TiO2 using model calculations and shown that the concentration of the dopant atoms near the surface of the TiO2 nanocrystals is larger than that near the core due to a 'self-purification mechanism'. A model for the observed decrease in the size of the iron doped nanocrystals of TiO2 is offered based on the above mechanism. Photoluminescence spectra (PL) of the samples confirmed the location of oxygen vacancy levels resulting from iron doping. The rapid decrease in the photocatalytic activity of the samples with higher concentrations of dopant is attributed to an increased number of the dopant ions near the grain boundaries caused by self-purification. In this article we show that the phenomenon of 'self-purification' is a real mechanism operative in nanocrystals and that this should be taken into account while analyzing the properties of doped nanocrystals for practical applications.