Unravelling the role of lithium and nickel doping on the defect structure and phase transition of anatase TiO2 nanoparticles

Anatase TiO2 nanoparticles doped either with Li or Ni have been synthesized via hydrolysis in variable concentrations. Microstructural analysis confirms the high crystallinity of the doped nanoparticles with sizes around 7 nm, while compositional analysis shows low doping below 2% at. Despite the low concentration of dopants, variations in the Raman and Photoluminescence signals were observed in the doped nanoparticles, mainly due to non-stoichiometry and oxygen deficiency promoted by Li or Ni doping. Doping effects associated with Li and Ni were observed by photoelectron spectroscopy and first principle calculations, which associate the appearance of states in the valence band region to oxygen deficiency and Li or Ni doping and lower n-type character induced by Ni doping. Finally, changes in the thermally induced anatase-to-rutile transition (ART) have been also observed in the doped samples, leading to a dopant-promoted faster ART which occurs at lower temperature boosted due to the dopant effect. Graphical abstract: [Figure not available: see fulltext.]