Sol–gel preparation and luminescent properties of CeO2:Ln (Ln = Eu3+ and Sm3+) thin films

New transparent CeO2:Ln (Ln = Eu3+ or Sm3+) thin-film phosphors have been fabricated by a sol–gel method. The CeO2:Ln films with the Ln concentrations of 1 at.% showed the strongest photoluminescence (PL) upon ultraviolet (UV) light excitation. At higher Ln concentrations, the PL intensity decreased because of the nonradiative energy transfer. For Eu3+ ions doped in the CeO2 lattice with inversion symmetry, an orangey red emission due to a magnetic-dipole 5D0 → 7F1 transition (591 nm) was dominant when excited at a wavelength of 340 nm. In contrast, much stronger orange emissions (573 nm) due to 4G5/2 → 6H5/2 were observed for Sm3+ ions. Apparently, the Eu3+ and the Sm3+ ions had different efficiencies of the excitation through the energy transfer from the “Ce4+–O2−” charge transfer state induced by the UV irradiation.