The synthesis of Er-doped TiO2 nanoparticles is made in this work by Ar/O-2 thermal plasma oxidation of a liquid precursor containing titanium butoxide and erbium nitrate, with varying Er3+ addition and O-2 input, Characterizations of the powders are achieved by chemical analysis, XRD, SEM, TEM, and EDS. The results show that the resultant powders are mixtures of anatase and rutile, whose anatase content increases at a higher O-2 input or at a lower Er3+ addition. The crystallite sizes of both anatase and rutile tend to decrease at a higher O-2 input, but anatase is always much finer than rutile. Er3+ cations are hardly dissolved in the TiO2 lattice but mainly formed Er2Ti2O7 pyrochlore, which tend to coexist with the rutile-rich larger (> 60 nm) particles in the powder. The synthesized particles show good cathodoluminescence at similar to 1530 nm due to I-4(13/2)-> I-4(15/2) transition of the electronic structure of Er3+. (c) 2005 Elsevier B.V. All rights reserved.