An energy transfer between the two parts of a nanocomposite was shown in a core-shell made of Tb-doped gadoliniurn oxide (the core) and polysiloxane (the shell). Polysiloxane is found to act as an antenna which absorbs light and transfers the excitation energy to the rare-earth doped oxide, allowing then an enhancement by a factor of 4 of the luminescence of the rare earth cations. Both energy transfer and quenching reduction contribute to the luminescence enhancement observed upon coating. The Letter shows how these relative contributions can be quantitatively discriminated from excitation spectra. (c) 2006 Elsevier B.V. All rights reserved.