Fluorine-doping in titanium dioxide by ion implantation technique

Pivotal Role of Fluorine in Tuning Band Structure and Visible‐Light Photocatalytic Activity of Nitrogen‐Doped TiO2

“…In line with earlier reports, [14][15][16][17] in the spin-unrestricted GGA calculation, the doping with nitrogen alone results in the formation of electron states in the band gap (about 1.10 eV above VB), [14,15] whereas the doping with F alone leads to the electron states below the bottom of the conduction band. [16,17] Interestingly, after co-doping of N and F, both VB and CB structures are significantly different from those doped separately with the two elements. First, similar to that in N-doped TiO 2 , electronic states above the VB also appear in the co-doped TiO 2 .…”

“…This extension is primarily due to the shift of the 3d states of Ti atoms adjacent to F into the band-gap, as reported earlier in the F-doped TiO 2 . [16,17] The electronic structure of N-doped TiO 2 has also been investigated by the spin-restricted calculations. [2,7] Our spinrestricted calculations show that both the pattern of total DOS and the electronic energy for N,F-co-doped TiO 2 are similar to those of the spin-unrestricted ones ( Figure S3), which is consistent with argument that the electrons from the N and F tend to be paired.…”

Absorption and action spectra analysis of ammonium fluoride-doped titania photocatalysts

“…34, 39 In most cases F-doping apparently did not cause any appreciable shift of the fundamental band gap absorption edge of TiO 2 . 30,35,37 This is consistent with the theoretical band calculations, 4,32 indicating that when TiO 2 is doped with fluorine, localized high density energy levels, composed of F 2p states, reside below the valence band of TiO 2 . But, in spite of this, F-doped materials exhibit visiblelight-driven photoactivity, whose origin is still very uncertain.…”

Electronic properties of F/Zr co-doped anatase TiO2 photocatalysts from GGA +U calculations

“…Todorova et al [17] have also reported F ions' incorporation into the TiO 2 lattice and attributed this to stronger absorption in the UV-visible region due to the presence of F -ions which favour formation of the anatase phase and improve the crystallinity of TiO 2 without changes in the band gap. On the other hand, Yamaki et al [18] have performed theoretical calculations of F-doped TiO 2 and reported modifications in the conduction band edge and the introduction of impurity states near its bottom. Some previous theoretical studies [8,19] have shown that F can neither narrow the band gap nor introduce impurities states into F-doped TiO 2 using standard density functional theory (DFT) calculations.…”

“…However, Di Valentin et al [20] [21] have synthesized F/Zr-codoped anatase TiO 2 and reported that synergetic effects are associated with electron transfer-mediated charge compensation between F/Zr impurities. Recently, there are many theoretical papers focused on explaining the microelectronic mechanisms of either monodoping by non-metal elements [8,18,19] A theoretical description of the localized atomic-like Ti 3d states induced by F ions or in the presence of oxygen vacancies is unable to provide satisfactory results in terms of either the local density approximation (LDA) or generalized gradient approximation (GGA), owing to the well-known band gap problem and the insufficient cancellation of the self-interaction energy. DFT+U methods can improve partially the prediction of the band gap, and are becoming increasing popular for the study of the electronic structures of semiconductors, and tend to produce more accurate results than those of standard DFT when used appropriately [20].…”