In the harmonic oscillator mode of an optical center in charge transfer (CT) excitation, the vibration frequency x (in ground state) and omega' (in CT state) would be decreased in nano-sized Y2O3:Eu3+, leading to the shrinkage in energy span E-span of CT excitation spectrum. The decrease of omega' results in the decrease of vibration energy E-vib of an optical center obtained in CT excitation. In addition, the zero-phonon CT energy E-zp is decreased with the decrease of phosphor size in nano-scale. Based on the changing magnitudes in E-zp and E-vib, the change in CT energy E-CT was obtained, which is basically consistent with that measured in the experiment. (C) 2013 Elsevier B. V. All rights reserved.