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Upconversion Sr 2 (Gd .98- x Er .02 Yb x ) 8 Si 6 O 26 (SGSO:2Er 3+ / x Yb 3+ ) phosphor materials were synthesized using a citrate sol-gel process. X-ray diffraction patterns confirmed their hexagonal structure. Field emission scanning electron microscopy images of SGSO:2Er 3+ / x Yb 3+ phosphors depicted submicron particles. The enhanced upconversion luminescence properties of SGSO:2Er 3+ / x Yb 3+ phosphors were analysed as a function of Yb 3+ ion concentration and laser power. The energy transfer induced enhanced emission of the Er 3+ / Yb 3+ ions co-doped SGSO phosphors was ascribed to multi-phonon relaxation. The calculated chromaticity coordinates of the SGSO:2Er 3+ / x Yb 3+ phosphors showed emissions could be tuned by changing Yb 3+ ion concentration. Optimized sample exhibited the chromaticity coordinate values near to the ultra-high definition television standard green emission coordinates. [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]

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]

Highlights: [•] RE ions triple-doped SrY2O4 nanocrystalline phosphors were prepared by sol–gel process. [•] SrY2O4:Er3+ ions single-doped phosphor exhibits deep green emission under NUV excitation. [•] Dy3+/Er3+ ions co-doped phosphor shows yellowish-green emission under 365nm excitation. [•] Er3+/Dy3+/Sm3+ triple-ions doped phosphor displays pleasant white emission for LEDs. [•] From CL, the triple-ions doped phosphor gives warm-white emission for FED applications. [ABSTRACT FROM AUTHOR]

A series of Dy3+ ion single-doped and Dy3+/Eu3+ ion co-doped white-light emitting SrY2O4 nanocrystalline phosphors were synthesized by a citrate sol–gel method. After the samples were annealed at 1300 °C, the X-ray diffraction patterns confirmed their orthorhombic structure. The particles were closely-packed and their optical properties were monitored by photoluminescence spectroscopy. The Dy3+ ions acted as luminescent centers and substituted Y3+ ions in the SrY2O4 host lattice, where they are located in Cs sites, and the characteristic emission of Dy3+ ions (4F9/2→6H15/2 and 4F9/2→6H13/2 transitions) with intense yellow emission band at 578 nm occurred. When the Eu3+ ions were co-doped into the SrY2O4:Dy3+ (1 mol%) nanocrystalline phosphor, white-light emission was observed under excitation at 381 nm. The energy transfer between Eu3+ and Dy3+ ions was calculated and the chromaticity coordinates were also presented. The cathodoluminescence (CL) spectra confirmed that the penetration depth is inversely proportional to the total atomic weight and atomic number of the compound. From CL analysis, the emission intensities of Dy3+ ion single-doped and Dy3+/Eu3+ co-doped SrY2O4 nanocrystalline phosphors increased continuously upon increasing both the accelerating voltage from 1 to 5 kV and the filament current from 30 to 47 μA. [ABSTRACT FROM AUTHOR]

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]

White light-emitting diode (WLED) products currently available on the market are based on the blue LED combined with yellow phosphor approach. However, these WLEDs are still insufficient for general illumination and flat panel display (FPD) applications because of their low color-rendering index (CRI < 75) and high correlated color temperature (CCT = 6000 K). Although near-ultraviolet (UV) LED chips provide more efficient excitation than blue chips, YAG:Ce3+ phosphors have very weak excitation in the near-UV spectral region. Hence, there is an increasing demand for novel yellow phosphor materials with excitation in the near-UV region. In this work, we report novel self-activated yellow Ca5Zn3.92In0.08(V0.99Ta0.01O4)6 (CZIVT) phosphors that efficiently convert near-UV excitation light into yellow luminescence. The crystal structure and lattice parameters of these CZIVT phosphors are elucidated through Rietveld refinement. Through doping with In3+ and Ta5+ ions, the emission intensity is enhanced in the red region, and the Stokes shift is controlled to obtain good color rendition. When a near-UV LED chip is coated with a combination of CZIVT and commercial blue Ba0.9Eu0.1MgAl10O17 phosphors, a pleasant WLED with a high CRI of 82.51 and a low CCT of 5231 K, which are essential for indoor illumination and FPDs, is achieved. [ABSTRACT FROM AUTHOR]

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]