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A series of Sr 3 Y 2 Ge 3 O 12 (SYGO), SYGO:Bi 3+ , SYGO:Eu 3+ and SYGO:Bi 3+ /Eu 3+ phosphors were synthesized by a facile pechini type sol-gel method. X-ray diffraction patterns exhibited a characteristic cubic lattice structure with a space group of la 3 ¯ d ( 230 ) after annealing at 1200 °C for 8 h. The morphological properties of the SYGO host lattice were studied by a field-emission scanning electron microscope, which displayed nearly spherical-shaped particles. Under ultraviolet (UV) or near-UV excitations, the SYGO:Bi 3+ phosphors showed the blue emission of Bi 3+ ( 3 P 1 → 1 S 0 ) at 467 nm and the SYGO:Eu 3+ phosphors exhibited orange red emission of Eu 3+ ( 5 D 0 → 7 F 1 ) at 594 nm, respectively. The energy transfer process was investigated in between the Bi 3+ and Eu 3+ ions by the wide spectral overlap of Bi 3+ emission spectrum and Eu 3+ excitation spectrum. The efficient energy transfer phenomenon from Bi 3+ to Eu 3+ ions was studied by adjusting the Eu 3+ ion concentration in SYGO:Bi 3+ /Eu 3+ phosphors and it was strongly confirmed by their luminescence decay curves. The critical distance was calculated for the energy transfer process from Bi 3+ to Eu 3+ ions due to the concentration quenching effect and it was further demonstrated to be a resonance type of quadrupole-quadrupole interactions. The obtained photoluminescence results revealed tunable emissions from blue to cool white, depending on the Eu 3+ ion concentration. Furthermore, the thermal properties and quantum yield of the optimized cool white-light emitting SYGO:0.02Bi 3+ /0.05Eu 3+ phosphor sample were studied and it exhibited good thermal stability with 20.5% quantum yield. Commission International de I'Eclairage chromaticity coordinates were calculated for all the prepared samples. Therefore, all these results indicate that the SYGO:0.02Bi 3+ /0.05Eu 3+ is a promising phosphor for the application of white light-emitting diodes. [ABSTRACT FROM AUTHOR]

Spherical yttrium gallium garnet (Y3Ga5O12) samples were prepared by a single-step hydrothermal synthesis method, and these particles were coated with silver oxide (Ag2O) nanoparticles by following a facile wet chemical approach at ambient temperature. The structural, morphological, vibrational and optical properties of the as-prepared and Ag2O modified Y3Ga5O12 samples were analyzed. From Rietveld refinement of X-ray diffraction patterns, the crystal structure of the Y3Ga5O12 sample was refined. The morphological properties confirmed that the particles were spherical and their surfaces were covered with Ag2O nanoparticles. The Ag2O modified Y3Ga5O12 sample exhibited a relatively enhanced photocatalytic activity compared to the pure Y3Ga5O12 sample in Rhodamine B solution, suggesting that the introduction of Ag2O broadens the absorption of light and controls the photogenerated carrier recombination in Y3Ga5O12. These results provide a clear perspective on the synthesis of hybrid photocatalyst materials which have several ways of photogenerated carrier migration. [ABSTRACT FROM AUTHOR]

The Y 6 WO 12 double oxide materials doped individually with rare-earth ions of Tm 3+ , Tb 3+ and Sm 3+ were prepared by a sol-gel method using citric acid as a complexing agent. The morphology of the prepared samples was studied using transmission electron microscope images and the crystallinity of the sample was confirmed by selective area electron diffraction patterns. The phase of the synthesized samples was analyzed by X-ray diffraction patterns and the optical properties were studied with photoluminescence (PL) and cathodoluminescence (CL) spectra. The emissions from the doped samples exhibited their respective colors both spectrally and to the naked eye under ultraviolet light excitation. Both PL and CL emission spectra showed the same results except the variation in the intensity of emission peaks. The activation energies calculated from the temperature-dependent PL spectra showed good thermal stability of the materials. The Commission International de I’Eclairage chromaticity coordinates calculated from the emission spectra were comparable to the standard phosphor used for lighting or imaging devices. [ABSTRACT FROM AUTHOR]

NaGdTiO 4 (NGT) phosphors doped with different activator ions (Tm 3+ , Dy 3+ , and Eu 3+ ) were synthesized by a conventional solid-state reaction method in an ambient atmosphere. These phosphors were characterized by scanning electron microscope images, transmission electron microscope images, X-ray diffraction patterns, Fourier transform infrared spectra, and photoluminescence spectra. All the samples were crystallized in an orthorhombic phase with a space group of Pbcm (57). In Tm 3+ /Dy 3+ ions co-doped samples, white-light emission was observed under near-ultraviolet (NUV) excitation. In addition, the energy transfer between Tm 3+ and Dy 3+ ions was proved to be a resonant type via an electric dipole–dipole mechanism and the critical distance of energy transfer was calculated to be 19.91 Å. Furthermore, Tm 3+ /Dy 3+ /Eu 3+ ions tri-doped NGT phosphors demonstrated warm white-light emission by appropriately tuning the activator content, based on the principle of energy transfer. These NUV wavelength excitable phosphors exhibit great potential as a single-phase full-color emitting phosphor for white light-emitting diode applications. [ABSTRACT FROM AUTHOR]

The rare-earth ions (Eu 3+ , Dy 3+ ) doped Y 6 WO 12 phosphors were prepared by a citrate-based sol–gel method. The morphologies and structural properties of the as-prepared and doped samples were analyzed by scanning electron microscope images and X-ray diffraction patterns. The luminescent properties were studied by examining the excitation and emission spectra of the samples. The Eu 3+ and Dy 3+ ions doped samples exhibited their characteristic emission bands in the visible region under ultraviolet light excitation. The temperature-dependent photoluminescence (PL) properties of the samples were also investigated. The PL spectra of the synthesized samples by the sol–gel method were compared with those of the bulk sample prepared by a solid-state reaction. Similarly, the Commission International de I’Eclairage chromaticity coordinates and the decay times of Y 6 WO 12 :Eu 3+ (3 mol%) and Y 6 WO 12 :Dy 3+ (2 mol%) phosphors were studied. [ABSTRACT FROM AUTHOR]

Spindle shaped tetragonal La2(MoO4)3: Eu3+ phosphors were synthesized by a polyol mediated solvothermal synthesis method. Growth mechanism for the formation of spindles was explained by increasing the reaction temperature. Similarly, the effect of EDTA concentration and calcination temperature on the morphology of particles was studied. Structural properties of the samples were analyzed by X-ray diffraction patterns and Fourier transform infrared spectra. The emission richness in the red region was investigated by measuring both photoluminescence (PL) and cathadoluminescence (CL) emission spectra. The excitation spectra of the samples at different calcination temperatures exhibited intense excitation bands at different wavelengths in the ultraviolet (UV)-A, UV-B, UV-C and visible regions. This property makes the sample to be a promising red region component in UV or visible excitation based white light-emitting diodes. The lifetime variation as a function of calcination temperature was observed. The CL spectra exhibited similar behaviors as the PL spectra except the considerable emission intensities in lower wavelength region. The CIE coordinates obtained from the PL and CL spectra provided a good chromaticity in the red region. [ABSTRACT FROM AUTHOR]

We synthesized the trivalent europium ions (Eu 3+ ) doped lanthanum aluminate (LaAlO 3 , LAO) nanophosphors by a solvothermal method. Their structural, morphological, and luminescent properties were systematically investigated. The obtained nanoparticles possessed single nanocrystallinity with a rhombohedral structure. For the excitation originating from the charge transfer band (O 2- to Eu 3+ ions) under 320 nm illumination, the featured emissions of Eu 3+ ions were detected in all the compounds. The optimum doping concentration of Eu 3+ ions in LAO was about 9 mol% and the concentration quenching was dominated by dipole-dipole interaction. Furthermore, the Judd-Ofelt (J-O) theory was used to estimate the J-O intensity parameters. Based on the temperature-dependent PL emission spectra, the thermal stability was analyzed and the activation energy was obtained to be 0.234 eV. Meanwhile, the decay time, color coordinate/purity, and cathodoluminescence behaviors of the synthesized nanophosphors were also studied. These characteristics make the Eu 3+ -doped LAO nanoparticles a promising red-emitting phosphor for both ultraviolet-based white light-emitting diodes and field-emission displays. [ABSTRACT FROM AUTHOR]