Luminescent properties of YVO4·xTa2O5:Eu3+

The samples of YVO4·xTa2O5:Eu3+(x=0.45,0.35,0.25,0.15,0.05)were synthesized by the conventional solid state reaction.The structure of the prepared sample was checked by the X-ray diffraction.XRD measurements at room temperature were confirmed that the prepared YVO4·xTa2O5:Eu3+ consisted of two phases。One phase was YVO4,which is tetragonal according with the JCPDS-Card(17-0341);the other phase was YTaO4,which is according with the JCPDS-Card(72-2018).The spectrum property of the sample was studied under the VUV.The effects of Ta doped on the luminescent properties of sample were investigated and it was found that some Ta doped could highlight the absorption of matrix in VUV region.The emission spectrum was dominated by the red peaks at 613 and 619 nm due to the electric dipole transition 5D0→7F2 of Eu3+.It indicated that Eu3+ occupied a site lacking inversion symmetry.There was one band peaked at 155 nm in the excitation spectrum of the sample,it could be assigned to the absorption of the host.     

Luminescent properties of SrSi2N2O2:Ce3+,Tb3+-a potential phosphor for white light emitting diodes

Ce3+ and Tb3+ co-doped SrSi2N2O2 phosphors were prepared by solid-state reaction. The X-ray diffraction pattern exhibited that the phosphor consisted mainly of oxygen-rich SrSi2N2O2. The optical properties of SrSi2N2O2:Ce3+, SrSi2N2O2:Tb3+ and SrSi2N2O2:Ce3+,Tb3+ were studied, respectively. The emission intensity of Tb3+ at 541 nm was remarkably enhanced by Ce3+ in SrSi2N2O2:Ce3+,Tb3+ phosphor, which was attributed to the energy transfer from Ce3+ to Tb3+. The chromaticity coordinates of phosphors were investigated as a function of Tb3+ concentration. When the Ce3+ and Tb3+ concentrations were 0.02 and 0.18 mol per formula unit, respectively, the chromaticity coordinate was (0.257, 0.337) in the CIE 1931 chromaticity diagram. SrSi2N2O2Ce3+,Tb3+ phosphors could be used for white light emitting diodes.     

Photoluminescence characterization and energy transfer of NaBa1-x-yPO4：xCe3＋, yTb3＋ phosphors

A series of NaBa1-x-yPO4: xCe3+, yTb3+ phosphors were synthesized by solid-state reaction method. The crystal structure, photoluminescence emission and excitation spectra and decay times of the phosphors were carefully investigated. The results revealed that an efficient energy transfer occurred from Ce3+ to Tb3+ ions in NaBaPO4 host by means of dipole-dipole interactions and the critical distance of the energy transfer was about 0.638 nm. Moreover, the phosphor emitted strong green emission under UV excitation, indicating that the phosphors are potentially useful as a highly efficient, green-emitting phosphor.     

Synthesis and luminescent properties of Eu3+doped Y2WO6 nanophosphors

Novel nanosized Y2WO6:Eu3+ phosphors were synthesized via a co-precipitation reaction. The crystal structure of Y2WO6:Eu3+sample was monoclinic phase characterized by using X-ray diffraction (XRD). The...     

Fabrication and luminescent properties of red phosphor M3BO6:Eu3+（M=La,Y）

A series of red phosphors M3BO6:Eu3+(M=La,Y) were synthesized at 1150 oC by conventional solid state reaction method and their luminescent properties were investigated.Structural characterization of the luminescent materials was carried out with X-ray powder diffraction(XRD) analysis.Photoluminescence measurements indicated that the La3BO6:Eu3+ phosphor exhibited bright red emission centered at about 612 nm 626 nm under UV excited.La3BO6:Eu3+ phosphor had better luminescent intensity than Y3BO6:Eu3+ phosphors under the same excitation and measuring conditions.It was shown that the 0.08 mol.% Eu3+ ions in La3BO6:Eu3+ phosphors was optimal.The color parameter indicated that La3BO6:Eu3+ phosphor was a preferable red phosphor for white LED.     

Facile sol-gel combustion synthesis and photoluminescence enhancement of CaZrO3：Sm3＋ nanophosphors via Gd3＋ doping

CaZrO3:Sm and CaZrO3:Sm,Gd nanophosphors were synthesized by a facile and efficient sol-gel combustion method. Their structure and optical properties were studied. The photoluminesce (PL) results showed that the phosphor could be efficiently excited by irradiation at wavelengths in the visible light region (350-430nm). The CaZrO3:Sm nanophosphor exhibited strong yellow-green, orange and red emissions with peak wavelength centered at 565nm (4G5/2→6H5/2), 601nm (4G5/2→6H7/2) and 645nm (4G5/2→6H9/2), respectively. The incorporation of Gd3+ ions could greatly improve the luminescence intensity. The highest emission intensity was observed with 2mol.% Gd3+ doped CaZrO3:3mol.% Sm powder. The material had potential application in the development of materials for LED’s and other optical devices in the visible region.     

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+.     

Luminescent properties of MMgP_2O_7：Eu~（3＋）（M=Ca,Sr,Ba） phosphor

A series of red phosphors Eu3+-doped MMgP2O7(M=Ca,Sr,Ba) were synthesized by solid-state reaction method.X-ray powder diffraction(XRD) analysis confirmed the formation of pure CaMgP2O7,SrMgP2O7 and BaMgP2O7 phase.Photoluminescence spectra of MMgP2O7(M=Ca,Sr,Ba):Eu3+ phosphors showed a strong excitation peak at around 400 nm,which was coupled with the characteristic emission(350-400 nm) from UV light-emitting diode.The CaMgP2O7:Eu3+,SrMgP2O7:Eu3+ and BaMgP2O7:Eu3+ phosphors showed strong emission bands peaking at 612,593 and 587 nm,respectively.Due to the difference of the ion sizes between Ba2+(0.142 nm),Sr2+(0.126 nm),Ca2+(0.112 nm),Mg2+(0.072 nm) and Eu3+(0.107 nm),Eu3+ ions were expected to substitute for different sites in CaMgP2O7,SrMgP2O7 and BaMgP2O7 lattice.     

Synthesis and luminescence properties of a novel phosphor Ca2–x/2Si1–xPxO4:Eu2+for near UV-excited white-light-emitting diodes

A novel green-emitting phosphor,Eu2+-doped Ca2-x/2 Si1-x Px O4(0.25≤x≤0.30),was prepared through a conventional solidstate reaction.X-ray diffraction(XRD),photoluminescence(PL) and decay studies were employed to characterize the sample,which was assigned to P63mc space group in the hexagonal system.The effect of P-doping on the α-Ca2 SiO4 was studied and P2 O5 broken down by the raw material of(NH4)2 HPO4 played an important role in stabilizing α-Ca2 SiO4 which can only be stable at high temperature.The XRD patterns of the Ca2-x/2 Si1-x Px O4 host were found pure and optimized when the mole fraction of P2 O5 was 14.5%.The diffuse reflectance spectra of the Ca1.855 Si0.71 P0.29 O4 and Ca1.845 Si0.71 P0.29 O4 :0.01Eu2+covered the spectral region of 230-400 nm,implying that the phosphor was suitable for UV or near-UV LED excitation.The phosphor could be effectively excited in the near UV region with the maximum at 372 nm.The emission spectrum of the Ca1.845 Si0.71 P0.29 O4 :0.01Eu2+phosphor showed an asymmetrical single intensive band centered at 513 nm,which corresponded to the 4f65d1→4f7transition of Eu2+.Eu2+ions might occupy two types of Ca2+sites in the Ca1.855 Si0.71 P0.29 O4 lattice and form two corresponding emission centers,which led to the asymmetrical emission of Eu2+in Ca1.855 Si0.71 P0.29 O4.The effects of Eu2+-doped concentration in Ca1.855-x Si0.71 P0.29 O4 :xEu2+on the PL were also discussed,the optimum doping concentration of Eu2+was 1 mol.% and the critical distance of the energy transfer was also calculated by the concentration-quenching method.The non-radiative energy transfer between Eu2+seemed to be caused by the multipole-multipole interaction.The fluorescence lifetime of Eu2+was found to be 0.55711 μs.The results suggested that these phosphors might be promising candidates used for near UV light excited white LEDs.     

Influence of oxygen non-stoichiometry on physical properties of NdSr2Mn2O7±δ

Nd Sr2Mn2O7+δ compounds were synthesized by ceramic method under three different cooling conditions. The Nd Sr2Mn2O7+δ samples were characterized by powder X-ray diffraction(XRD). Oxygen non-stoichiometry data for the studied powders were determined by using gravimetric and X-ray photoelectron spectroscopy(XPS) methods. The correlation of cooling method and oxygen as non-stoichiometry was established. The electroconductivity in samples was studied by using four-point probe method, and the strong correlation with non-stoichiometry was found out. Magnetization measurements were carried out. It was found that the magnetic and transport properties of the samples were also influenced by oxygen non-stoichiometry. The evolution of the magnetic properties could be explained by the formation of magnetic clusters in the vicinity of oxygen vacancies(OV) and strong competition between the superexchange and double exchange interactions.     

Tunable color emission in K3Gd（PO4）2:Tb3+,Sm3+ phosphor for n-UV white light emitting diodes

A series of K3Gd(PO4)2:Tb3+,Sm3+ phosphors were synthesized through solid state reaction. By co-doping Tb3+ and Sm3+into K3Gd(PO4)2 host and singly varying the doping concentration of Sm3+, tunable colors from green to yellow and then to orange were obtained in K3Gd(PO4)2:Tb3+,Sm3+ phosphors under the excitation at 373 nm. The energy transfer process from Tb3+ to Sm3+ was verified through luminescence spectra and fluorescence decay curves. Moreover, the energy transfer mechanism was demonstrated to be the quadrupole-quadrupole interaction. The results indicated that K3Gd(PO4)2:Tb3+,Sm3+ phosphors could be a potential application for n-UV white light emitting diodes.     

Controlled synthesis and luminance properties of lanthanide-doped β-NaYF4 microcrystals

Hexagonal Yb3+,Er3+-doped Na YF4 crystals with different morphologies were synthesized by a facile hydrothermal method at 140–200 oC. Their shape and size could be controlled by varying hydrothermal temperature, time and doping effect of Ce3+ ions. Interestingly, the products displayed hexagonal sheet, plate, crown-like prism to tube changes in the temperature range from 140 to 200 oC. A combination of diffusion-controlled growth and selective adsorption was proposed to understand the formation of the Na YF4 crystals with well-defined shapes. Na YF4:Yb3+/Er3+ crystals exhibited shape-dependent up-conversion(UC) luminescence under excitation of 980 nm, and their luminescence property could be tuned by doping Ce3+ ions.     

Luminescence properties of Eu3＋ and Ho3＋ in SreTiO4

Eu3+ and Ho3+ doped Sr2TiO4 were synthesized by using solid-state reactions. Samples sintered at 1300 oC for 6 h could be indexed to Sr2TiO4 with a single phase. Eu3+ in Sr2TiO4 emitted orange light under the excitation at 365 nm in a broad band which was coupled well with the strongest emission of high pressure mercury vapor lamps. Ho3+ in Sr2TiO4 emitted yellow light under blue excitation from 450 to 460 nm which agreed well with the emission of blue InGaN-based light-emitting diodes. The present results indicated that Sr2TiO4 was a promising host for high pressure mercury vapor lamps or white light-emitting diodes.     

Hydrogen storage properties of mechanically milled La2Mg17-x wt.% Ni （x=0, 50, 100, 150 and 200） composites

Melting method was used to obtain La2Mg17 alloy,and then Ni powder was added by mechanical alloying method.The kinetics of hydriding process and electrochemical properties of La2Mg17-x wt.%Ni(x=0,50,100,150,200) composites were investigated.X-ray diffraction(XRD) and scanning electron microscopy(SEM) analyses showed that the crystal structure of composite alloy gradually transformed into amorphous phase by the effect of ball milling and Ni powders.The research of hydrogen absorption properties found that La2Mg 17-50 wt.%Ni reached the highest hydrogen absorption than other alloys with more addition of Ni content,reached to 5.796 wt.% at 3 MPa,and up to 5.229 wt.% merely in 2 min,which revealed that the amorphous phase reduced the H occupation of the lattice clearance,resulting in the decline of hydrogen absorption capacity.The electrochemical tests indicated that the maximum discharge capacity increased to 353.1 mAh/g at 30 oC,however,the cycle stability decreased considerably.A series of kinetic measurements demonstrated that the controlling steps of electrochemical process of La 2 Mg 17-x wt.%Ni alloys transferred from hydrogen diffusion on alloy bulk(x=50,100) to hydrogen diffusion on both alloy bulk and surface(x=150,200).     

Effect of RO （R=Ca, Sr, Ba, Zn or Pb） component on spectroscopic properties of Eu3＋ in RO-B2O3 glasses

Eu3+-doped binary borate glasses with different metal oxide components RO (R=Ca, Sr, Ba, Zn or Pb) were prepared by meltquenching technique. The fluorescent spectral properties of Eu3+in these glasses were experimentally studied. The analysis on the phonon sidebands (PSBs) indicated that RO component did not cause obvious change of the electron-phonon coupling constant (EPC). By inspecting the optical absorption edges it was found that RO could greatly affect the band gap energy, and the glass with PbO component revealed the smallest band gap energy, the glasses with ZnO, BaO and SrO showed similar band gap energy. The optical transition intensity parameters of Eu3+in all studied glasses were calculated, it was found that for each sample its value of2 was larger than that of 4 and 6, and the sample with PbO component exhibited the smallest2, but the λ values for ZBE, CBE, BBE and SBE were very similar. These results might be helpful for the design of borate glasses.     

Optical and thermoluminescence properties of Lu2Si2O7：Pr single crystal

Single crystal of Lu2Si2O7:Pr was grown by Czochralski method. Transmittance, photoluminescence excitation (PLE) and photo-luminescence (PL) spectra, X-ray excited luminescence (XEL) and fluorescence decay time spectra of the sample were measured and discussed to investigate its optical characteristics. The crystal structure of the as grown Lu2Si2O7:Pr was confirmed to be C2/m. There was a broad absorption peaking at 245 nm in the region from 200-260 nm. The PL spectrum was dominated by fast 3PJ→3HJ band peaking at 524 nm. The XEL spectrum was dominated by the fast 5d14f1→4f2 emission peaking at 265 nm. The 2D (temperature-intensity) and 3D (temperature-wavelength-intensity) thermally stimulated luminescence (TSL) spectra were measured. The Pr3+ ion was found to be the recombination center during the TSL process. Three obvious traps were detected in LPS:Pr single crystal with energy depth at 1.06, 0.78 and 0.67 eV.     

Influence of urea on microstructure and optical properties of YPO4：Eu^3＋ phosphors

YPO4:Eu 3+ phosphors were synthesized by solution coprecipitation method assisted by urea in the precursor reaction solution. X-ray diffraction spectral analysis showed that the samples synthesized with urea had smaller particle size and lower crystallinity than those samples synthesized without urea.Moreover,the calculated strain result indicated that the Eu 3+ site in the former exhibited a lower crystal field symmetry than that in the latter.Hence,the influence of crystal field symmetry dominated luminescence efficiency rather than crystallinity because the luminescence intensity observed in Eu0.05Y0.95PO4 synthesized with 1.0 g urea was six-fold higher than that of the as-synthesized sample.With increased concentration of Eu 3+ ion,the luminescence intensity initially increased,and then subsequently decreased as the concentration of Eu 3+ ion exceeded 12 mol.%due to concentration quenching.The optimal condition for YPO4:Eu 3+ phosphor was Eu0.12Y0.88PO4 with 1.0 g urea added in the precursor.The luminescence intensity of the optimal condition was again enhanced 1.6-fold relative to that of Eu0.05Y0.95PO4 synthesized with 1.0 g-urea.     

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.     

Structural and superconducting properties in Y0.6Gd0.4Ba2（Nb）Cu3O7-y cuprates doped with niobium

Polycrystalline YBa2Cu3O7-y (YBCO) and Y0.6Gd0.4Ba2-xNbxCu3O7-y (YGBNCO) compounds with 0≤x≤0.225 were synthesized using standard solid state reaction technique. The structure for all samples was characterized by X-ray difference (XRD) and scanning electron microscopy (SEM). The transport properties were measured by the (FPP) method in the temperature range from 70 to 130 K. As the Nb content in the samples increased, a diffused phase indicating a niobium perovskite phase and a small amount of unidentified phase appeared. With the increase of Nb content, the superconducting transition temperature Tconset increased slowly with x≤0.125, and then it remained unchanged or slowly decreased with 0.125≤x≤0.225. It could be found that there was a slow decrease of zero-resistance temperature, Tcoffset, with the increase of Nb content. The larger transition width might result from the YBa2NbO6 phase, impurity and unidentified phases of the sample due to the Nb doping.     

Synthesis and electrochemical properties of Ce-doped LiNi_（1/3）Mn_（1/3）Co_（1/3）O_2 cathode material for Li-ion batteries

The layered material of Ce-doped LiNi1/3Mn1/3Co1/3O2 with α-NaFeO2 was synthesized by a co-precipitation method. X-ray diffraction (XRD) showed that Ce-doped LiNi1/3Mn1/3Co1/3O2 had the same layered structure as the undoped LiNi1/3Mn1/3Co1/3O2. The scanning electron microscopy (SEM) images exhibited that the particle size of Ce-doped LiNi1/3Mn1/3Co1/3O2 was smaller than that of the undoped LiNi1/3Mn1/3Co1/3O2. The Ce-doped LiNi1/3Mn1/3Co1/3O2 samples were investigated on the Li extraction/insertion performances through charge/discharge, cyclic voltammogram (CV), and electrochemical impedance spectra (EIS). The optimal doping content of Ce was x=0.02 in the LiNi1/3-xMn1/3Co1/3CexO2 samples to achieve high discharge capacity and good cyclic stability. The electrode reaction reversibility was enhanced, and the charge transfer resistance was decreased through Ce-doping. The improved electrochemical performances of the Ce-doped LiNi1/3Mn1/3Co1/3O2 cathode materials were attributed to the addition of Ce4+ ion by stabilizing the layer structure.