Based upon the local structure data, the differences of energy bands between bulk and nano-sized Y2O3:Eu3+ have been presented. The volume expansion in nano-sized Y2O3:Eu3+ leads to the shrinkage of band gap and decrease of zero-phonon charge transfer (CT) energy; the enlargement of local disorder in nano-sized Y2O3:Eu3+ leads to the formation of impurity bands and further decrease of zero-phonon CT energy. On the basis of the differences in energy bands, the mechanisms for the decrease of CT energy, i.e., red shift of CT excitation spectra for nano-sized Y2O3:Eu3+ have been clarified. (C) 2010 Elsevier B. V. All rights reserved.