Interplay of Vanadium States and Oxygen Vacancies in the Structural and Optical Properties of TiO₂:V Thin Films

Abstract

In this work, we present the customized modifications in the morphology and optical properties of vanadium (V) doped TiO 2 thin films sputter deposited on glass substrates at a growth rate of ∼0.6 Å/s at 500 °C. The sputtering targets of pure and V doped TiO 2 with three concentrations of V (1.0, 1.5, and 2.0 atomic percentage (at. %)) were prepared from powders. XRD patterns confirmed the grown TiO 2 films were anatase. In the doped TiO 2 films, the crystallite size reduced by almost half when the V concentration increased from 0 to 2 at. % systematically. Incorporation of V in the TiO 2 host lattice led to the enhanced growth of (211) planes, which significantly modified the grain geometry from the faceted to the elongated as observed in the SEM images and confirmed by structural simulation using VESTA code. The confinement of phonon modes was observed in the Raman spectra, which was attributed to the increased nonstoichiometry and enhanced asymmetry in bonding with increased V concentration. XPS spectra confirmed that the enhancement in the nonstoichiometry in TiO 2 was due to V substitution in the structure. It was suggested that the difference in the valence states of Ti and V resulted in the suppression of equilibrium (101) planes and augmentation of nonequilibrium (211) planes, which modified the grain morphology of the TiO 2 thin films. Photoluminescence (PL) spectroscopy clearly demonstrated the interplay of V defect states and O vacancy states. Pure TiO 2 showed mainly green luminescence related to oxygen vacancies; however, addition of V clearly demonstrated orange and red emission bands due to incorporation in V 3+ and V 5+ states, which increased at a much faster rate than oxygen vacancies on further addition of V. The PL results complimented the XPS findings.

Facile synthesis and photocatalytic activity of a novel titanium dioxide nanocomposite coupled with zinc porphyrin

“…The oxide particles with a high density of oxygen vacancies can give rise to in-gap states or surface states that yield a continuum of below bandgap absorbances. 24,25 Such defects may be the origin of the observed photoluminescence in the wavelength range from 450 nm to 575 nm. There is a decrease in photoluminescence intensity in proceeding from bare TiO 2 to the nanocomposite sample expect to a broad band around 593 nm.…”

Crystalline Mixed Phase (Anatase/Rutile) Mesoporous Titanium Dioxides for Visible Light Photocatalytic Activity

“…54,55 The green curve at 520 eV corresponds to the O 1s satellite. 56 The results of curve fitting in Figure 5c suggest that all samples contain V 5+ species. Moreover, one can clearly observe a shoulder in the 5% V-Ti-700, 10%V-Ti-700, and 10%V-Ti-800 samples, which can be assigned to the V 4+ species.…”

Bandgap engineering of oxygen-rich TiO2+x for photocatalyst with enhanced visible-light photocatalytic ability

“…However, its efficiency is limited by its wide bandgap (*3.0 eV) because it could be activated only under the UV irradiation, and the photoinduced electron-hole pairs can recombine easily as well. To reduce the bandgap and improve the efficiency, considerable experimental and theoretical efforts have been carried out, such as doping (including metal, non-metal, and codoping) [2,[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22], defect engineering (including oxygen vacancy and Ti interstitial) [23][24][25][26][27][28][29][30][31], and surface coating (such as metal and semiconductor nanoparticles) [32][33][34][35][36]. Recently, Etacheri et al [37] reported that the visible-light photocatalytic activity of undoped TiO 2 was achieved by increasing the amount of oxygen in TiO 2 .…”