In this paper, we report a facile method for synthesis of ultra small (1-3 nm) gadolinium oxide (Gd2O3) nanoparticles using citric acid (CA) as a capping agent. The dependence of nanoparticle (NP) size on the ratio between CA and gadolinium (Gd) is investigated. Absorption properties of the ultra small Gd2O3 NPs in UV region have four characteristic peaks at 312 nm, 274 nm, 253 nm and 228 nm. Finally, we show that the Gd2O3 nanoparticles synthesized by this method induce triplet emission (phosphorescence) from CA and EG in the NIR region. (C) 2010 Elsevier Inc. All rights reserved.