Synthesis and photoluminescence studies of Ba(Gd,Ln)B9O16:Eu3+(Ln=La,Y) phosphors for n-UV LED lighting and display devices

BaGdB9O16:Eu3+ and Ba(Gd,Ln)B9O16:Eu3+(Ln=La, Y) phosphors were synthesized by solid state diffusion method. The X-ray diffraction, scanning electron microscopy(SEM) and photoluminescence properties were investigated. The as-synthesized BaGdB9O16:Eu3+ and Ba(Gd,Ln)B9O16:Eu3+(Ln=La, Y) phosphors showed strong red emission under ultraviolet light excitation. By partially substituting Gd3+ by La3+ and Y3+ ions in the host BaGdB9O16:Eu3+ materials, the maximum emission intensity was observed for the optimum composition of BaGd0.91La0.8B9O16Eu0.01 phosphor. The experimental results indicated that the Eu doped BaGdB9O16 and Ba(Gd,Ln)B9O16(Ln=La, Y) phosphors were promising red phosphors, which might find potential applications in near-UV excited LED lighting as well as display devices. Comparison of as-synthesized phosphors with standard phosphor used in CFL(compact fluorescent lamp) was also done. Energy transfer mechanism of Gd3+ to Eu3+ was also discussed in this paper.     

Photoluminescence properties of nanosized strontium-yttrium borate phosphor Sr3Y2（BO3）4：Eu^3＋ obtained by the sol-gel Pechini method

Mixed strontium-yttrium borate phosphor Sr3Y2(BO3) 4 doped with Eu3+ ions was obtained by the sol-gel Pechini method.Crystal structure of the synthesized compound was analyzed by X-ray powder diffraction.Optimal conditions for the synthesis were found.Photo-physical properties of the phosphor samples were investigated by collecting excitation and luminescence spectra as well as measuring lumi-nescence lifetime.Judd-Ofelt analysis showed that Eu3+ ions occupied Y3+ sites in the crystalline network.The studied compound showed a red emission with the quantum yield of 54%-55% and can be potentially used as phosphor for plasma display panels and luminescent tubes.     

Nanocrystalline rare earth fluorides doped with Pr~(3+) ions

Praseodymium(Ⅲ) doped CeF_3, CeF_3:Gd, LaF_3, GdF_3 and YF_3 inorganic fluorides were precipitated in an aqueous, surfactant-free solution, using NH_4 F as a source of fluoride ions. The as-prepared products were subjected to a hydrothermal treatment, which led to the formation of crystalline nanoluminophores, composed of spherical(≈30 nm) and elongated(≈40–200 nm) nanostructures. Due to the presence of Pr~(3+) ions, the synthesized nanomaterials showed yellow luminescence under a blue light irradiation. The nanoluminophore based on the YF_3 host revealed the most promising spectroscopic properties, i.e., bright and intensive emission, hence it was investigated in detail. The photophysical properties of the nanomaterials obtained were studied by powder X-ray diffraction(XRD), transmission electron microscopy(TEM) and spectrofluorometry, i.e., measurements of excitation/emission spectra and luminescence decay curves.     

Effect of synthesis conditions and surrounding medium on luminescence properties of YVO4:Eu3+nanopowders

Nanocrystalline yttrium vanadate doped with europium ions powders were synthesized via sol-gel method based on decomposition of metal-polymer complex. X-ray diffraction analysis showed that samples had pure tetragonal phase without any impurities. Scanning electron microscopy and static light scattering technique were used to study morphology and size of prepared nanoparticles. Average diameter of the nanoparticles was about 40 nm. The changes in structural and luminescence properties were observed as a function of the first and second calcination temperature. The optimal conditions for synthesis of nanoparticles were determined as Т1=500 °С, t1=1 h; Т2=950 °С, t2=1.5 h. The effect of different media surrounding the nanoparticles on their luminescence properties and lifetime was investigated and discussed in terms of effective refractive index. It was found that the observed lifetime of YVO4:Eu3+ 5 at.% nanophosphor was decreased from 0.64 ms in air(nmed=1) to 0.45 ms in chalcogenide glass As39S61(nmed=2.39).     

Synthesis and spectral characteristics of La2MoO6：Ln3＋ （Ln=Eu, Sm, Dy, Pr, Tb） polycrystals

The novel phosphors of La 2 MoO 6 activated with the trivalent rare earth Ln 3+ (Ln=Eu, Sm, Dy, Pr, Tb) ions were synthesized by solid state reactions at high temperature in air atmosphere, and their phase impurities and luminescent properties were studied. The photoluminescence (PL) excitation and emission spectra, and decay curves were employed to study their luminescence properties. The lifetimes of the characteristic emissions from Ln 3+ ions were in the order of millisecond except Pr 3+ ions. (LaEu 1-x ) 2 MoO 6 was a promising phosphor for practical application and the optimum concentration was x=0.075. The concentration quenching mechanism of Eu 3+ was also discussed by theoretical fitting using Burshtein model.     

Luminescent properties of Eu~（3＋） doped Gd_2WO_6 and Gd_2（WO_4）_3 nanophosphors prepared via co-precipitation method

Eu3+ doped Gd2WO6 and Gd2(WO4)3 nanophosphors with different concentrations were prepared via a co-precipitation method. The structure and morphology of the nanocrystal samples were characterized by using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), respectively. The emission spectra and excitation spectra of samples were measured. J-O parameters and quantum efficiencies of Eu3+ 5D0 energy level were calculated, and the concentration quenching of Eu3+ luminescence in different matrixes were studied. The results indicated that effective Eu3+:5D0-7F2 red luminescence could be achieved while excited by 395 nm near-UV light and 465 nm blue light in Gd2WO6 host, which was similar to the familiar Gd2(WO4)3:Eu. Therefore, the Gd2WO6:Eu red phosphors might have a potential application for white LED.     

Preparation and luminescent properties of CaAl_2O_4:Eu~(3+),R~+(R=Li,Na,K) phosphors

CaAl2O4:Eu3+,R+(R=Li+,Na+,K+) red phosphors were synthesized by solid state reaction method.X-ray diffraction(XRD) and photoluminescence(PL) were employed to characterize their structural and luminescent properties.It was found that the optimal sintering temperature and sintering time were 1200 °C and 4 h,respectively.The optimal concentration of doped Eu3+ was 3 mol.%.Furthermore,under ultraviolet excitation with a wavelength of 254 nm,these samples showed red luminescence which were probably attributed to the transitions from 5D0 excited state to 7FJ(J=0-4) ground states of Eu3+ ions.The feature and the high intensity of hypersensitive transition from 5D0→7F2 indicated that Eu3+ preferred to occupy a low symmetry site.The incorporation of alkali metal ions greatly enhanced the luminescence intensity probably due to the influence of charge compensation of alkali metal ions.     

Synthesis and photoluminescence properties of ZnTiO3:Eu3+ red phosphors via sol-gel method

ZnTiO3:Eu3+ phosphors were synthesized with different concentrations of Eu3+ doping through sol-gel method. The samples were calcined at different temperatures for 2 h in air. The synthesized powders were characterized by X-ray diffraction(XRD), scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS), transmission electron microscopy(TEM), Raman and photoluminescence spectroscopy. The XRD results showed that the Zn Ti O3:Eu3+ phosphors doped with different concentrations of Eu3+ ions calcined at 600 oC were of single phase, which indicated that the Eu3+ ions had been successfully incorporated into the Zn Ti O3 host lattice and did not destroy the lattice structure of Zn Ti O3 host. The Raman spectrum, SEM and TEM also proved that the doping of Eu3+ did not change the lattice structure of hexagonal Zn Ti O3 host. The photoluminescence(PL) of Eu3+ ions with the main emission peak at 614 nm was observed to increase with Eu3+ concentrations from 0.5 mol.% to 2.0 mol.% and decreased when the concentration was increased to 2.5 mol.%. The decrease in the PL intensity at higher Eu3+ concentrations could be associated with concentration quenching effect. The CIE1931 chromaticity diagram(x, y) of Zn Ti O3:2.0 wt.%Eu3+ phosphors were located in the red region(x=0.652, y=0.347). The luminescence properties suggested that Zn Ti O3:Eu3+ phosphors might be regarded as a potential red phosphor candidate for light emitting diodes(LEDs).     

An impact of sintering temperature and doping level on structural and spectral properties of Eu-doped strontium aluminium oxide

In the present work,a sol-gel method was employed to prepare nanosized SrAl2O4 powders doped with Eu3+ ions.The raw nano-materials were thermally treated at 900 to 1100 oC for 3 h.The XRD analysis demonstrated that the powders were single-phase nanopowders with high crystallite dispersion.Our studies were focused on relating the luminescence properties of the Eu3+ dopant to the NC(nanocrystal-lites) size.This was achieved by varying the calcinations temperature between 900 and 1100 oC.The average NC size varied accordingly be-tween ～36 and ～75 nm.We found that size effect manifested mainly in the expansion of the cell volume and broadening of XRD peaks as in-dicated by Rietveld analysis.Moreover the emission and excitation spectra,although typical for Eu3+ ions,demonstrated some degree of variability with calcinations temperature and doping concentration.To explain these differences a detailed analysis of luminescence spectra by the Judd-Ofelt theory was performed.     

Synthesis of CaWO4：Eu3＋ phosphor powders via ethylene glycol route and its optical properties

Eu3+ doped CaWO4 with tetragonal system were prepared at comparatively low temperature (125 ?C) in ethylene glycol medium. The phosphor was further investigated by X-ray diffractometer (XRD), photoluminescence spectrophotometer (PL), Fourier transform infra red (FT-IR) spectroscopy and transmission electron microscopy (TEM). XRD analysis indicated a decrease in the unit cell volume of CaWO4 with increasing Eu3+ ion concentration. It indicated the homogeneous substitution of Ca2+ ions in CaWO4 by the Eu3+ ions. TEM images showed that the particle size ranged from 20 to 200 nm and it could extend the application of the nanoparticles. The photoluminescence study showed that the intensity of electric dipole transition (5D0→7F2) at 614 nm dominated over the magnetic dipole transition (5D0→7F1) at 592 nm. The optimum concentration of Eu3+ for the highest luminescence was found to be 20 at.%. The as prepared samples were found to be dis-persible in water and methanol.     

Solvothermal fabrication and luminescent properties of Eu2＋/Ce3＋ doped barium lithium fluoride

Phosphors of BaLiF3 doped with Eu or/and Ce were solvothermally prepared at 200°C for 5d and characterized by means of X-ray powder diffraction (XRD) and environment scanning electron microscopy (ESEM). The excitation and emission spectra of the rare earth ions doped BaLiF3 were measured by fluorescence spectroscopy and the effects of Ce3+ ions on the luminescence of Eu2+ ions were investigated. In the codoped Eu2+ and Ce3+ system, the emission intensity of Eu2+ ion gradually increased with the Ce3+ concentration increasing, and the enhancement of Eu2+ fluorescence was due to efficient energy transfer from Ce3+ to Eu2+ in the host.     

Emission of Eu3＋ in sol-gel oxyfluoride glass materials obtained by different preparation methods

Silica glasses doped with Eu3+ ions prepared by sol-gel methods were investigated. The X-ray diffraction(XRD) was used to verify the nature of the studied systems. Excitation and emission spectra of Eu3+ ions in sol-gel glass materials were detected. Red-to-orange luminescence intensity ratios R/O related to integrated intensities of 5D0→7F2 to 5D0→7F1 transitions and luminescence lifetimes for 5D0 state of Eu3+ ions were determined. The results indicated that spectroscopic parameters for Eu3+ ions strongly depended on reagents and their relative ratios used for sol-gel glass preparation.     

Energy transfer from Tb³⁺ to Eu³⁺ in zinc lead borate glass

In order to sensitize the luminescence of Eu3+ ions in heavy metal glass,zinc lead borate glass samples containing various concentrations of Eu3+ and Tb3+ ions were prepared to study the Tb3+ to Eu3+ non-radiative energy transfer phenomena.Energy level structures of Tb3+ and Eu3+ ions were plotted to show the excitation and energy transfer routes.Efficient energy transfer from Tb3+ to Eu3+ was observed and studied qualitatively in terms of doping concentrations.The sensitization turned out to be less effective than expected.Further studies to characterize the oxidation of Tb3+ into tetravalent state and to examine the mechanism of energy transfer are proposed.     

Luminescent properties of dysprosium（Ⅲ） ions in LaAlO3 nanocrystallites

The absorption and emission spectra as well as decay time profile of Dy3+ ions in LaAlO3 nanocrystals were analyzed.The crystal structure of LaAlO3 was confirmed from XRD measurement.The emission peaks from blue to red came from main emitting level of dyspro-sium 4F9/2 to the ground and other excited levels of Dy3+ ions.Cross relaxation process led to non-radiative quenching of luminescence,so that the lifetime of the 4F9/2 energy level ions decreased with increasing amount of doped Dy3+ ions.The cross relaxation transfer rates were ex-perimentally determined as a function of Dy3+ concentration.     

Effect of gadolinium incorporation on optical characteristics of YNbO_4：Eu~（3＋） phosphors for lamp applications

Eu3+-doped (Y,Gd)NbO4 phosphor was synthesized by solid-state reaction for possible application in cold cathode fluorescent lamps. A broad absorption band with peak maximum at 272 nm was observed which was due to the charge transfer between Eu3+ ions and neighboring oxygen anions. A deep red emission at the peak wavelength of 612 nm was observed which could be attributed to the 5D0→7F2 transition in Eu3+ ions. The highest luminance for Y1-x-yGdyNbO4:Eux3+ under 254 nm excitation was achieved at Eu3+ concentration of 18 mol.% (x=0.18) and Gd3+ concentration of 8.2 mol.% (y=0.082). The luminance of Y0.738Gd0.082NbO4:Eu3+0.18 was higher than that of a typical commercial phosphor Y2O3:Eu3+ and the CIE chromaticity coordinate was (0.6490, 0.3506), which was deeper than that of Y2O3:Eu3+. The particle size of the synthesized phosphors was controlled by the NaCl flux and particle size as high as 8 μm with uniform size distribution of particles was obtained.     

Investigations on Valence-Change Behaviors of Europium Ions in Eu-Doped Aluminate and Silicate Phosphors

Compounds of Sr3Al2O6∶Eu, Sr4Al14O25∶Eu, and BaZnSiO4∶Eu were synthesized by high-temperature solid state reactions. The doping Eu3 ions were partially reduced to Eu2 in Sr4Al14O25∶Eu and BaZnSiO4∶Eu prepared in an oxidizing atmosphere, N2 O2. However, such an abnormal reduction process could not be performed in Sr3Al2O6∶Eu, which was also prepared in an atmosphere of N2 O2. Moreover, even though Sr3Al2O6∶Eu was synthesized in a reducing condition CO, only part of the Eu3 ions was reduced to Eu2 . The existence of trivalent and divalent europium ions was confirmed by photoluminescent spectra. The different valence-change behaviors of europium ions in the hosts were attributed to the difference in host crystal structures. The higher the crystal structure stiffness, the easier the reduction process from Eu3 to Eu2 .     

A novel long lasting phosphor Sr5 （PO4）3FxCll_x：Eu2＋,Gd3＋ prepared in air condition

A series of blue long afterglow mixed halide-phosphate phosphors Sr5 （PO4）3 FxCll-x：Eu2＋,Gd3＋ were synthesized in air by traditional solid-state reaction routte. The crystal structures, photoluminescence, thermolurninescenee properties and afterglow proper- ties of the phosphors were characterized systematically using X-ray diffraction （XRD）, luminescence spectrophotometer, microcom- puter thermoluminescence dosimeter and single photon counter, respectively. Under 280 nm excitation, the broadband emissions of Eu2＋ ions were observed at 445 nm （blue） due to the 4f7→4f65d transition. It was demonstrated that there existed the self-reduction of the Eu3＋ to Eu2＋ ions in this special halide-phosphate matrix in air condition. The addition of Gd3＋ ions obviously enhanced the after- glow properties of the single doped Eu2＋ ions in the halide-phosphate phosphors. And the content of the fluoride anions also had sig- nificant influence on the afterglow properties. All results indicated that Srs （PO4）3 FxCI1-x：Eu2＋,Gd3＋ might be potential phosphors for long lasting phosphorescence （LLP） materials.     

Energy transfer processes from Yb3＋ to Ln3＋ （Ln=Er or Tm） in heavy metal glasses

Heavy metal glasses doubly doped with Yb3+ and Ln3+ ions(Ln=Er or Tm) were studied. Glass host matrices were limited to lead borate glass and lead germanate glass. Efficient resonant(Yb3+-Er3+) and non-resonant(Yb3+-Tm3+) energy transfer was observed for the studied systems. Near-infrared luminescence spectra at 1.53 μm(Er3+) and 1.9 μm(Tm3+) were detected under excitation of Yb3+ by 975 nm diode laser line. They corresponded to 4I13/2→4I15/2(Er3+) and 3F4→3H6(Tm3+) transitions of rare earth ions, respectively. The unusual large spectral linewidth nearly close to 110 nm for 4I13/2→4I15/2 transition of Er3+ ions in lead borate glass was obtained, whereas long-lived near-infrared luminescence at 1.53 μm was detected in lead germanate glass. Quite different situation was observed for Yb3+-Tm3+ doubly doped glasses. In contrast to lead borate glass, near-infrared(3F4→3H6) luminescence spectra were registered for Tm3+ ions in lead germanate glasses, only. These phenomena strongly depended on stretching vibrations of glass host, which was confirmed by FT-IR spectroscopy.     

Effect of trivalent rare earth ions doping on the fluorescence properties of electron trapping materials SrS：Eu~（2＋）

Trivalent rare-earth ions (La3+,Pr3+,Nd3+,Sm3+,Gd3+,Tb3+,Dy3+,Ho3+,Er3+,Tm3+,and Yb3+) were investigated as the codoped auxiliary sensitizer for the electron trapping materials SrS:Eu2+ in order to enhance the fluorescence properties.It was found that Sm3+ and Tb3+ had the best photoluminescence stimulated luminescence (PSL) effect among the selected trivalent rare-earth ions.All the SrS:Eu2+ samples doped by different trivalent rare-earth ions could be stimulated by 980 nm laser after being exposed to the conventional sunlight,and they emitted PSL with the peak located at 615 nm.The result also indicated that some co-doped rare earth ions could increase fluorescence intensities of the traditional electron trapping materials SrS:Eu2+.     

Electroluminescent Property of A Novel Co-Doped Rare Earth Complex

A novel co-doped rare earth complex Gd0.5Eu0.5（TTA）3Dipy was synthesized and chosen as the emitter material in the organic electroluminescent device ITO/PVK：Gd0.5 Eu0.5 （TTA）3Dipy/PBD/A1. It was proved that there was Forster energy transfer from Gd^3＋ to Eu^3＋. The electroluminescent mechanism of the device was proposed by measuring and analyzing the emission and the excitation spectra of the emissive layer. Gd^3＋ might play the role of promoting the en- ergy transfer from PVK to Eu^3＋ and inhibiting an intrinsic luminescence of PVK. The device displayed red light with good monochromaticity. The possible energy transfer process of the device was preliminarily discussed.