(Eu3+–Nb5+)-codoped TiO2 nanopowders synthesized via Ar/O2 radio frequency thermal plasma oxidation processing: Phase composition and photoluminescence properties through energy transfer

(Eu3+–Nb5+)-codoped TiO2 nanopowders have been prepared by Ar/O2 radio frequency (RF) thermal plasma oxidizing liquid precursor mists, with various addition contents of dopants (molar ratio of Eu3+:Nb5+ = 1:1). Characterizations have been performed by the combined studies of XRD, TEM, Raman spectra, UV–vis spectroscopy, and excitation and PL spectra. The plasma-generated nanopowders mainly consist of anatase and rutile polymorphs. Doping Nb5+ cannot have appreciable influence on Eu3+ solubility (0.5 at.%) in the TiO2 host lattice, but can significantly inhibit the increase of rutile weight fraction for TiO2. 617 nm PL intensity at 350 nm indirect excitation through energy transfer is considerably weaker than that at 467 nm direct excitation, indicating that a defect state level in the TiO2 host lattice might be lowered below the excited state of Eu3+ by doping Nb5+, which is conceivable from a relatively large amount of oxygen deficiencies yielded in the TiO2 host lattice.