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.

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Lu(6)WO(12) and Lu(6)MoO(12) doped with Eu(3+) ions have been prepared by using a citrate complexation route, followed by calcination at different temperatures. The morphology, structure, and optical and photoluminescence properties of the compounds were studied as a function of calcination temperature. Both compositions undergo transitions from a cubic to a hexagonal phase when the calcination temperature increases. All the compositions have strong absorption of near-UV light and show intense red luminescence under a near-UV excitation, which is related to the transfer of energy from the host lattices to dopant Eu(3+) ions. Density functional theory calculations have also been performed. The calculation reveals that hexagonal Lu(6)WO(12) and Lu(6)MoO(12) are indirect bandgap materials, and the near-UV excitations are due to the electronic transitions from the O-2p orbitals to W-5d and Mo-4d orbitals, respectively. The lattice parameters and bandgap energies of hexagonal Lu(6)WO(12) and Lu(6)MoO(12) were determined.

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Trivalent dysprosium‐doped cubic yttrium oxide (Y2O3) nanophosphors were prepared by combustion synthesis using glycine as fuel. The resulting products were characterized by Raman and FT‐IR spectra to evaluate the vibrational features of the samples. X‐ray diffraction patterns confirmed the formation of a pure cubic phase of Y2O3. The morphology and selective area electron diffraction measurements were carried out using transmission electron microscopy (TEM) and field‐emission scanning electron microscopy. From TEM, it is observed that as‐prepared particles have average crystallite sizes of around 23 nm. The luminescent and dynamic properties of Y2O3:Dy3+ were examined as a function of temperature and different concentrations of Dy3+. The luminescence study reveals that these phosphors predominantly exhibit greenish‐yellow emission due to strong 4F9/2→6H13/2 transition at 575 nm and a feeble 4F9/2→6H15/2 transition at 488 nm. These results show that the relative luminescence intensity of emission bands changes with different heating temperatures, while the greenish yellow color luminescence as well as Commission International d'Eclairage chromaticity coordinates extracted from the emission spectra were not affected significantly. The strong greenish‐yellow emission of Y2O3:Dy3+ phosphor may be useful for applications in solid‐state white lamps for general illumination purposes.