Nanocrystalline Eu3+-doped CeO2, CeO2, Sm3+-doped CeO2, and Li+, Eu3+-codoped CeO2 samples were prepared through a sol−gel process. The structure and the optical properties of the samples were characterized by X-ray diffraction, diffuse reflection spectra, and photoluminescence spectra. No luminescence was observed for nanocrystalline CeO2. The systematic investigation shows that the broad band in the excitation spectrum of CeO2:Eu3+ comes from the charge transfer (CT) transition from O2− to Ce4+, not from the oxygen vacancy, or from the CT of O2− to Eu3+. Upon increasing the fired temperature from 600 to 800 °C, the excitation spectrum shifts to lower energy. With increasing concentrations of Eu3+ up to 1% in CeO2, red shifts of the excitation spectra are observed; however, when the concentration of Eu3+ increases to 5% and 10%, blue shifts occur. The emission spectrum shows that the symmetry of the Eu3+ site becomes lower with increasing Eu3+. Based on the dielectric theory of complex crystals, the environmental factor (h e) and the dielectric definition of average energy gap around the centers of Eu3+ are calculated. The reasons for the shifts of the excitation spectra are discussed in detail.

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Trivalent dysprosium (Dy3+)‐doped NaCaPO4 phosphors were synthesized by using a conventional solid‐state reaction technique. The phase and the structure of the as‐prepared powders were characterized by using X‐ray diffraction analysis and revealed that the pure NaCaPO4 formed with orthorhombic structure. The photoluminescence excitation and emission spectra were measured to characterize the luminescent properties of NaCaPO4:Dy3+ phosphors. Sharp emission peaks were observed at 482 nm (blue) and 575 nm (yellow) upon 367 nm excitation, which are attributed to the characteristic 4F9/2→6HJ (J=15/2 and 13/2) transitions of trivalent Dy3+ ions, respectively. The suitable control of the blue/yellow intensity ratio is expected to realize a white luminescent system. The lifetime of 4F9/2 level was measured by exciting Dy3+ ions at 355 nm excitation. The chromaticity coordinates were calculated from the emission spectra and analyzed with Commission International de I'Eclairage (CIE) programs and diagrams. The CIE color coordinates fall in the white light region under different ultraviolet (UV) excitations. These results indicate that NaCaPO4:Dy3+ phosphor could be a potential candidate for UV‐based white light‐emitting diodes.