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Abstract Energy conservation and environmental safety are the key requirements in the modern world. We report novel orange-emitting double perovskite Ba 2 LaNbO 6 :Eu3+ (BLN:Eu3+) nanophosphor fabricated using a citrate sol-gel method for use in general illumination and photocatalysis. After annealing at 800 ℃, the particles exhibited a nanorod-like morphology with monoclinic structure. The photoluminescence emission spectra exhibited an intense 5D 0 →7F 1 transition at 594 nm and a moderate 5D 0 →7F 2 transition at 615 nm, demonstrating that the Eu3+ ions occupied the La3+ sites with inversion symmetry. The optimal concentration of Eu3+ ions was found to be about 5 mol% for the BLN host lattice. Energy transfer from the NbO 6 7- octahedrons to the Eu3+ ions was clearly witnessed when the BLN:Eu3+ nanophosphors were excited with both the characteristic excitation bands of Eu3+ (7F 0 →5L 6) and NbO 6 7- octahedrons at 392 and 380 nm, respectively. The thermal quenching temperature of 5 mol% Eu3+ ions doped BLN nanophosphors was found to be 183 ℃, indicating that these nanophosphors are very stable at high temperatures. In addition, the dye removal efficiency of the proposed BLN nanophosphors was verified using Rhodamine B (RhB) dye as a model pollutant under UV irradiation. Compared to a commercial nano-ZnO catalyst, our synthesized BLN nanophosphors showed superior RhB de-colorization efficiency. Therefore, the proposed BLN:Eu3+ nanophosphors are promising multifunctional materials for photocatalysis and general lighting applications. [ABSTRACT FROM AUTHOR]

Fluorescence intensity ratio (FIR)-based optical thermometry has attracted a great deal of attention because it allows accurate and reliable temperature measurements with high spatial resolution and real-time monitoring. Herein, we report the novel Sr 2 Gd 8 (SiO 4 ) 6 O 2 :Er 3+ (SGSO:Er 3+ ) phosphor as an optical thermometry material. The sol-gel method is used to synthesize the oxyapatite structured SGSO:Er 3+ phosphors, which exhibits a rod-like morphology. The photoluminescence spectra of SGSO:Er 3+ phosphors displays two distinct green emission bands corresponding to the electronic transitions 2 H 11/2  →  4 I 15/2 and 4 S 3/2  →  4 I 15/2 . The temperature-induced variations in the FIR result in a maximum sensitivity of 3.4 × 10 −3  K −1  at 463 K. Further, the CIE chromaticity coordinates do not shift from the green region when the temperature is increased from 303 to 483 K and the color purity only decreasing from 77.6 to 71.4%. The SGSO:2Er 3+ phosphor exhibits the color-purity of 93.5% when excited with low-energy electron beam. These results suggest that the SGSO:2Er 3+ phosphor is a promising material for optical temperature sensors and display devices. [ABSTRACT FROM AUTHOR]

To meet the requirements of warm white light-emitting diodes (WLEDs) with extreme thermal stability, high color rendering index and low color temperature, which is equivalent to natural sunlight, we need to develop novel phosphor materials that can efficiently absorb excitation energy from near-ultraviolet (NUV) LEDs and produce desired visible emissions. The Sr 2+ and Eu 2+ ions co-activated Ba 2 SiO 4 ((BaSr)Si:Eu 2+ ) green-emitting nanophopshors for NUV or blue excitation-based WLEDs are reported. After annealing at 1300 °C, the X-ray diffraction patterns established the pure orthorhombic phase of (BaSr)Si:Eu 2+ nanophosphors. The evolution of (BaSr)Si:Eu 2+ nanorods from the surface of the sub-micron sized (BaSr)Si:Eu 2+ particles showed a tremendous effect on the luminescent properties by enhancing the transmittance of the (BaSr)Si:Eu 2+ nanophosphor. The incorporation of Sr 2+ ions along with Eu 2+ ions into the Ba 2+ sites, the emission intensity was increased, and also the quantum efficiency was enhanced from 47 to 59%. Upon excitation at 370 nm, the Ba 2 SiO 4 :Eu 2+ phosphor exhibited a bluish-green emission while the yellowish-green emission was revealed by the (BaSr)Si:Eu 2+ nanophosphor. The thermal stability of the (BaSr)Si:Eu 2+ nanophosphor was verified at elevated temperatures and the activation energy for thermal quenching was found to be 0.38 eV. When the (BaSr)Si:Eu 2+ nanophosphor was coated on a NUV LED chip, the enriched green emission was observed by increasing the input current from 100 to 250 mA. The (BaSr)Si:Eu 2+ is expected to be a promising green-emitting phosphor material for the fabrication of NUV or blue excitation-based warm WLEDs for general illumination. [ABSTRACT FROM AUTHOR]

Tb 3+ ions activated Ba 4 La 6 O(SiO 4 ) 6 (BLSO:Tb 3+ ) phosphors were synthesized by a citrate sol-gel method. The X-ray diffraction pattern confirmed their oxyapatite structure. The field-emission scanning electron microscope image established that the BLSO:Tb 3+ phosphor particles were closely-packed and acquired irregular shapes. The photoluminescence (PL) excitation spectra of BLSO:Tb 3+ phosphors showed intense f–d transitions along with low intense peaks corresponding to the f–f transitions of Tb 3+ ions in the lower energy region. The PL emission spectra displayed the characteristic emission bands of Tb 3+ ions, and the optimized concentrations were found to be at 1 and 6 mol% for blue and green emission peaks, respectively. The cathodoluminescece (CL) spectra exhibited a similar behavior that was observed in the PL spectra except the intensity variations in the blue and green regions. The CL spectra of the BLSO:6 mol% Tb 3+ phosphor unveiled accelerating voltage induced luminescent properties. [ABSTRACT FROM AUTHOR]

Single, double and triple trivalent rare-earth (RE3+ = Dy3+, Tm3+, Tm3+/Dy3+ and Tm3+/Dy3+/Eu3+) ions activated Sr2Gd8(SiO4)6O2 (SGSO) phosphors were synthesized by a sol–gel process. X-ray diffraction profiles confirmed their oxyapatite structure after annealing at 1450 °C for 12 h. Morphological studies were performed by taking scanning and transmission electron microscopy images, which displayed rod-like shapes. SGSO phosphors exhibited good photoluminescence (PL) properties in the respective regions when doped with Dy3+ and Tm3+ ions. Dy3+ co-activated SGSO:Tm3+ phosphors revealed tunable emissions from cool white light to warm white light towards the yellow region based on the co-activator concentration. However, Eu3+ ions co-doped SGSO:Tm3+/Dy3+ phosphors tuned the emissions towards the red region. The energy transfers from Tm3+ to Dy3+ ions and Tm3+/Dy3+ to Eu3+ ions were established based on the energy level diagram. The cathodoluminescence properties of these phosphors showed excellent emission behavior when the single, double or triple trivalent RE ions were doped into the SGSO host lattice. Unlike the case of the PL, the energy transfer process was observed to take place. The calculated Commission Internationale de l'Eclairage chromaticity coordinates of Tm3+ and Dy3+ individual ion doped SGSO phosphors confirmed the blue and white emissions, while the co-doped samples exhibited tunable emissions. [ABSTRACT FROM AUTHOR]

A series of Dy 3+ ions activated CaGd 2 ZnO 5 (CGZO) nanophosphors were synthesized by a modified citrate sol–gel method. The X-ray diffraction pattern confirmed their orthorhombic structure. The field-emission scanning electron microscope images established that the CGZO particles acquired irregular shapes within the nanometer range. The photoluminescence (PL) excitation spectra of CGZO:Dy 3+ showed a strong host absorption band along with low intense peaks corresponding to the f–f transitions of Dy 3+ ions, indicating that efficient energy transfer occurred between the CGZO host lattice and Dy 3+ ions. The PL emission spectra exhibited the characteristic emission bands of Dy 3+ ions ( 4 F 9/2 → 6 H 15/2 at 486 nm and 4 F 9/2 → 6 H 13/2 at 572 nm) with high intense yellow emission and the optimized concentration was found to be 1 mol% in this CGZO host lattice. The cathodoluminescence spectra also showed a similar behavior that observed in the PL spectra and the emission intensities of the CGZO:1Dy 3+ nanophosphor increased continuously with increasing the accelerating voltage and filament current. These novel nanophosphors are expected to have potential applications in the fields of optical displays and field-emission display systems. [ABSTRACT FROM AUTHOR]

Red color-emitting CaGd2ZnO5:Eu3+ (CGZO:Eu3+) nanophosphors were synthesized by a facile sol–gel process. The structural and luminescent properties of these phosphors were investigated as a function of annealing temperature and Eu3+ ion concentration. The orthorhombic phase was confirmed at different annealing temperatures, showing an irregular morphology within the nanoscale range. Photoluminescence (PL) excitation spectra of CGZO:Eu3+ showed host absorption band (HAB), charge transfer band (CTB), and intense f–f transitions of Eu3+ in the violet and blue wavelength regions. The CTB intensity increased and the HAB intensity decreased with increasing annealing temperature or Eu3+ ion concentration. The CGZO:Eu3+ exhibited a strong absorption in the blue region as compared to the CTB and had a superior property compared to available commercial phosphors. This feature facilitates the fabrication of high color rendering index white light-emitting diodes for display systems. In PL spectra, an intense red emission was observed due to the hypersensitive 5D0→7F2 transition with good asymmetry ratio and chromaticity coordinates. Optimized annealing temperature and concentration of Eu3+ ions were observed for CGZO host lattice based on the 466 nm excitation wavelength. The cathodoluminescent properties were also similar to the PL results. [ABSTRACT FROM AUTHOR]

Abstract: Ca2Gd8(SiO4)6O2 (CGS) nanophosphors with different concentrations of single-doped Dy3+ ions and co-doped Dy3+/Eu3+ ions were prepared by a solvothermal synthesis. Very fine particles in the nanometer range could be achieved by this method, as evidenced by transmission electron microscope measurements. The hexagonal phase of the oxyapatite structure was confirmed by X-ray diffraction patterns. The energy transfer between Eu3+ and Dy3+ ions was investigated by photoluminescence excitation and emission properties. These phosphors had absorption bands in the UV and NUV region, which are suitable for the emission wavelength of UV or NUV light-emitting diodes (LEDs). With increasing the Eu3+ ion concentration, the emission peak intensity corresponding to the 5D0→7F2 transition increased and the yellow (4F9/2→6H13/2) emission intensity also increased compared to the blue (4F9/2→6H15/2) emission intensity due to the increased energy transfer between Dy3+ to Eu3+ ions. Thus, the Eu3+ ions compensated the red emission component of the Dy3+ doped CGS nanophosphors. Such phosphors are expected to have potential applications for NUV based white LEDs. [Copyright &y& Elsevier]

Abstract: We reported the novel red-emitting phosphors of trivalent europium (Eu3+) ions activated CaGd4O7 (CG) prepared by a sol–gel method. After the samples were annealed at 1500°C, the X-ray diffraction patterns confirmed their monoclinic structure and the transmission electron microscopy image showed the nanocrystallinity of the CG: Eu3+ phosphor. The photoluminescence excitation spectra exhibited the efficient energy transfer from the Gd3+ to Eu3+ by overlapping the f–f transition of Gd3+ excitation band with charge transfer band of Eu3+ ions. The photoluminescence (PL) spectra showed the emission band in the entire visible region at lower Eu3+ concentration and the red emission at higher Eu3+ concentration. All the decay curves were well fitted by single exponential functions. The temperature dependent luminescence measurements were performed for identifying the thermal stability of CG: Eu3+ phosphors at elevated temperatures. The cathodoluminescent (CL) spectra also presented a similar behavior to that observed in PL spectra. Form the PL, CL, and decay analysis the optimum concentration of Eu3+ ions in the CG host lattice was found to be 5mol%. The CIE chromaticity coordinates varied from yellow to red in visible spectral region by increasing the Eu3+ concentration. [Copyright &y& Elsevier]

Abstract: Blue and green light emissive nanocrystalline Ca2Gd8Si6O26 (CGS):Tm3+ and CGS:Er3+ phosphors with high color purity were prepared by solvothermal reaction method. The structural and morphological properties of these phosphors were evaluated by the powder X-ray diffraction (XRD) and scanning electron microscopy, respectively. From the XRD results, Tm3+:CGS and Er3+:CGS phosphors had the characteristic peaks of oxyapatite in the hexagonal lattice structure. The visible luminescence properties of phosphors were obtained by ultraviolet (UV) or near-UV light and low voltage electron beam (0.5–5kV) excitation. The photoluminescence and cathodoluminescence properties were investigated by changing the variation of Tm3+ or Er3+ concentrations and the acceleration voltage, respectively. The CGS:Tm3+ phosphors exhibited the blue emission due to 1D2→3F4 transition, while the CGS:Er3+ phosphors showed the green emission due to 4S3/2→4I15/2 transition. The color purity and chromaticity coordinates of the fabricated phosphors are comparable to or better than those of standard phosphors for lighting or imaging devices. [Copyright &y& Elsevier]