The interaction of CeO2 nanoparticles with CF4 gas at high temperature results in the formation of CeF3 Crystalline phase on the surface of nanoparticles. The lattice parameters of CeF3 phase in CeO2/CeF3 composite nanoparticles correspond to CeF3 bulk. In the process of formation of CeF3 crystalline phase, the Ce3+ ions can occupy the various positions in crystal lattice: normal sites and perturbed sites arising due to location of O-2(-) ions near to Ce3+ ions. The energy transfer between Ce3+ ions occupying normal and perturbed sites in CeF3 phase has been observed. (C) 2018 Elsevier B.V. All rights reserved.