Effect of lattice distortion on bandgap decrement due to vanadium substitution in TiO2 nanoparticles

Abstract

Here we present a simple and effective way of bandgap tuning by V-substitution in TiO2. The nanoparticles of Ti(1-x)VxO2 (for 0≤x≤0.09) were prepared by controlled and simplified sol-gel method. The pure anatase phase of TiO2 was confirmed by X-ray diffraction and Raman spectroscopy. Debye-scherrer formula and Williamson-Hall plot give crystallite size decreases from 10.8 to 8.2nm when strain increases from 0.019 to 0.027 for x=0 to x=0.09. Rietveld refinement show the systematic change in crystal structure with the amount of V-substitutions. Raman shift and broadening of FWHM of first Eg (145.52cm−1) mode observed in Raman spectroscopy follow interestingly the similar and correlated observation with XRD outcomes. FESEM and UHRTEM represent pictorial view of the morphology of the nanoparticles with information about different micro-agglomerations and crystallinity. The oxidation states and local environment of elements in nanoparticles were studied using XANES. V-substitution in TiO2 shows band gap moderation: band gap decreases gradually with substitution from 3.06–2.02eV as concentration of V increases from x=0.0 to 0.09. This extends the application of TiO2 in UV as well as visible light whereas the application of pure TiO2 is limited in only UV region. The results of SEM, XRD, Raman spectroscopy and UV-vis spectroscopy are correlated well with lattice distortion and the lattice distortion gives the Urbach energy. We reach to the conclusion that the effective bandgap decreases may be due to creation of impurity energy levels or Urbach energy tails just above valance band and below conduction band.