The temperature and particle size dependence of the holewidths for the 7F0 → 5D0 transition of Eu3+ ions in Eu2O3 are calculated and compared with experiment. The calculation is able to describe the effect of nanocrystal vibrational modes on the dephasing of the electronic states of probe ions. The nanocrystal was treated as an elastically isotropic sphere from which the acoustic phonon displacements and phonon spectrum were calculated. Then we applied this to the temperature and size dependencies of the electron-phonon interaction. Also the vibrational modes in nanocrystals are discussed.