Effect of MgF2-H3BO3 flux on the properties of (Ce,Tb)MgAl11O19 phosphor

The green-emitting(Ce,Tb)MgAl11O19(CTMA) phosphor was prepared by the conventional high temperature solid-state reaction method.The effect of fluxes on the crystal structure,particle morphology,size distribution and photoluminescence properties of CTMA phosphor was investigated by means of the X-ray powder diffraction,scanning electron microscopy and photoluminescence spectrum.The results showed that the addition of appropriate amount of MgF2-H3BO3 flux improved the phase purity of CTMA phosphor,and influen...     

Preparation and Luminescent Properties of BAM Blue Phosphor forPDP and CCFL

The Bax-0.05MgAl10O16 x :Eu0.05^2 (0.88≤ x≤ 1.02) phosphors with different Ba^2 content and the Ba0.85MgAl10O16.94:Eu0.05^2 phosphors with different fluxes (BaF2, MgF2, AlF3, BaCl2, MgCl2, AlCl3, H3BO3)were prepared by high temperature solid-state reaction method and their luminescence characteristics were studied under 254 nm excitation and vacuum ultraviolet (VUV) excitation. With the increase of the Ba^2 content, there is an increase in the emission intensity, and when x = 0.94, it reaches a maximum. Then, as the Ba^2 content increases, the emission intensity slowly falls. The fluorides have better flux-effects than chlorides and H3BO3. The possible mechanism in the process of particle growth was discussed when fluorides were used as fluxes. The effect of the activator concentration on this system was also investigated. The quenching concentration is 0.13 mol in per mole host.     

Luminescent properties of amorphous phosphor 1.4YeO3·2.5Al2O3·0.1Tb2O3 prepared by sol-gel method

Amorphous phosphor 1.4YeO3·2.5Al2O3·0.1Tb2O3 （the same composition as Y2.8Tb0.2Al5O12） was prepared via a sol-gel method at relatively low temperature （i.e., below 650℃）, which is much lower than that for the preparation of polycrystalline Y3Al5O12：Tb^3＋ （above 1400℃）. The amorphous phosphor prepared in the optimized conditions showed a bright green-yellowish luminescence, the intensity of which was comparable with that of polycrystalline sample and the emissions of which were assigned to 5D4 → 7Fj transitions of Tb^3＋. Besides the emissions of Tb^3＋, the amorphous samples prepared at temperatures below 500 ℃ presented a weak blue emission band around 420 nm.     

Factors affecting afterglow properties of red-emitting phosphor MgSiO3：Mn^2＋,Nd^3＋ for luminescent fiber

With stable physical properties,the rare-earth silicate phosphor of MgSiO3:Mn2+,Nd3+ is one of the suitable luminescent materials used in preparing functional fibers.In order to promote the afterglow properties of red-emitting phosphors,we prepared it by means of solid-state reaction,and the effect of manufacturing elements including H3BO3 and environmental factor of calcining temperature,type of flux on its luminescence property were investigated through evaluating their afterglow properties.The results showed that with the concentration of Nd 3+ increasing,the amounts of H3BO3 doping and calcining temperature,the afterglow time and initial brightness of the rare-earth silicate phosphor increased and then decreased gradually.The afterglow properties of different flux concentration were different from one to another as:H3BO3 >Na+>K+>No flux.     

Preparation! of High Color Rendering Index Phosphor（Gd, Ce, Tb） （Mg, Mn） B5O10

The Ce^3 , Tb^3 and Mn^2 co-activated high color rendering index phosphor (Gd,Ce,Tb)(Mg, Mn)B5O10 was synthesized by ceramic method.The effects of synthetic conditions, such as the amount of boracic acid, Tb/Ce ratio, the concentration of hydrogen in nitrogen, the calcination temperature, on the luminescence properties were studied. It is shown that the high rendering index phosphor can be obtained when the amount of of boracic acid is added in 8% extra,     

Synthesis of Spherical （Y, Gd） BO3 ： Eu^3＋ Phosphor Using W/O Emulsion System

Spherical （Y, Gd）BO3：Eu^3＋ phosphor particles with a narrow size distribution（2 -4 μm） was obtained by firing the Y-Gd-Eu-BO3 precursor prepared in a W/O style emulsion system. In the W/O emulsion system, kerosene, used as oil phase, was mixed with Span 80 and Tween 80 compounds which were employed as the emulsifier with an HLB （hydrophile-lipophile balance） value of 5.2- 5.3. Both rare earths （Y, Gd and Eu） nitrate and boric acid solution or ammonia solution were used as aqueous phase. The synthesis conditions, such as emulsion composition, emulsifying style, precipitation reaction process, reaction temperature, morphology control, and so on, were investigated, and the optimum synthesis conditions for preparing spherical （Y, Gd）BO3：Eu^3＋ phosphor was obtained. The phosphor was characterized by XRD, SEM, laser particle size analysis, emission and excitation spectrum under vacuum ultraviolet （VUV）, and so on. The phosphor synthesized using the water-in-oil emulsion method with median diameter （D50） of 2 - 4 μm shows agreeable photoluminescence （PL） property and sphericity. The main emission peak appears at about 593 nm, which corresponds to ^5D0→^7F1 transition （magnetic-dipole transition） of the Eu^3＋ ion. The cell parameters and powder diffraction data were indexed. The structure of the phosphor belongs to the hexagonal system with space group P63/m.     

Synthesis of Long Afterglow Phosphor CaAl2Si2O8 ：Eu^2＋, Dy^3＋ via Sol-Gel Technique and Its Optical Properties

The long afterglow phosphor CaAl2Si2O8：Eu^2＋ , Dy^3＋ was prepared by a sol-gel method. The sol-gel process and the structure of the phosphor were investigated by means of X-ray diffraction analysis （XRD）. It is found that the single anorthite phase formed at about 1000 %, which is 300 % lower than that required for the conventional solid state reaction. The obtained phosphor powders are easier to grind than those of solid state method and the partical size of phosphor has a relative narrow distribution of 200 to 500 nm. The photoluminescence and afterglow properties of the phosphor were also characterized. An obvious blue shift occurs in the excitation and emission spectra of phosphors obtained by sol-gel and solid state reaction methods. The change of the fluorescence spectra can be attributed to the sharp decrease of the crystalline grain size of the phosphor resulted from the sol-gel technique.     

Influence of Molten Salt on Luminescent Intensity and Particle Size of Y2O3 ：Eu^3＋ Phosphor

The Y-Eu oxalate precursor was prepared with a homogeneous precipitation method. And the additives, Na2CO3, S, NaCl or their combination, were introduced into the precursor to prepare Y2O3 ：Eu^3＋ red phosphors at 1000 1300 ℃ for 2 h. The effect of molten salts on particle size and luminescent intensity was studied. The experimental results showed that the complex molten salt （Na：CO3 ＋ S ＋ NaCl） was conductive to enhance the luminescent intensity of Y2O3 ：Eu^3＋. The emission intensity of the phosphor prepared with these additives at 1300 ℃ was about 45% higher than that of the one prepared without molten salt, and about 11% higher than that of the corresponding commercial phosphor. Meanwhile, the particle size of Y2O3 ：Eu^3＋ phosphor was controlled effectively with the molten salt.     

Preparation and photoluminescence of Tb^3＋ doped SrAl2O4 phosphor by composite combustion method

High-efficient Tb^3＋ activated SrAl2O4 phosphor was synthesized by a combined combustion-solid-state reaction method. The precursor of SrAl2O4：Th^3＋ phosphor was prepared via a combustion process, and then the as-prepared powder was heated in a reductive ambient of activated carbon at 1250 ℃ for 1 h. The results of X-ray diffraction, scanning electron microscopy, and photoluminescence spectra revealed the influence of the dosage of urea and heated process on the crystallinity, morphology, and photoluminescence of the phosphor. Comparing with traditional solid-sate reaction, the crystallinity and emission intensity of the SrAl2O4：Tb^3＋ phosphor were improved by this two-step process.     

Photoluminescence of Dy^3＋ Ions in Ba3La（B03）3

The photoluminescence of Dy^3 doped and Dy^3 , Ce3 codoped in Ba3La(BO3)3 were studied. The dependence of the charge-to-radius ratio (z/r) for RE^3 (RE=La,Ce), the Ce^3 , Dy^3 content on the emission intensity and the yellow to blue intensity ratio (Y/B) of Dy^3 were investigated too. The results obtained indicate that Ce^3 can sensitize the luminescence of Dy^3 .The optimum concentration of Dy^3 in Ba3La(BO3)3 is XDy=0.06. According to the dependence of the concentration of Dy^3 in Ba3La(BO3)3 under the excitation of 350 nm, it is confirmed that the mechanism of concentration selfquenching of Dy^3 4F9/2→6H15/2, ^6H13/2 transition is electric dipole-quadrupole interaction.     

A Study of Scandia Doped Tungsten Nano-Powders

Scandia and rhenium doped tungsten powders were prepared by solid-liquid doping combined with two-step reduction method. The particle size of doped tungsten and distribution of scandia and rhenium were studied by SEM, EDS, XRD and granularity analysis. Experimental results showed that scandia distributed evenly on the surface of tungsten particles. Addition of scandia and rhenium decreased the particle size of doped tungsten, and the more the content of scandia and rhenium, the smaller the doped tungsten particles. Tungsten powders doped with 3 % Sc2O3 and 3 % Re （mass fraction） had an average size of about 80 nm in diameter. The mechanism of the decrease in the tungsten particle size was discussed.     

Exploring a particle-size-reduction strategy of YAG:Ce phosphor via a chemical breakdown method

Particle size reduction of Y_3 Al_5 O_(12):Ce(YAG:Ce) phosphor is highly needed for micro-LED display applications.In this work,size control of YAG:Ce phosphor particles is achieved via carbon coating and further heat treatment.A thin layer of carbon is deposited on the surface of YAG:Ce by chemical vapor deposition.During the heat treatment,carbon reacts with oxygen element in the phosphor and escapes from phosphor particles.The reaction results in the phosphor breaking into smaller particles.The phosphors were characterized by laser light scattering for particle size distribution,scanning electron microscopy(SEM),transmission electron microscopy for morphologies,X-ray diffraction refinements for crystal structure and electron energy-loss spectroscopy for elemental analysis.It is demonstrated that the median diameter(D_(50)) of the phosphor particle size is significantly reduced from 19.1 to 0.96 μm yet the photoluminescent properties have little changes.The carbon coating and further heat treatment method show potential application in size control of phosphors.     

Effect of LowFrequency AC Power Supply During Electroslag Remelting on Qualities of Alloy Steel

The effect of frequencies of AC power supply on the quality of the electroslagmelted ingot is studied. The results show that with a decrease in the frequency, electromagnetic force becomes more violent, and the temperature in the slag bath becomes more homogeneous, and therefore, the depth of molten metal pool is decreased; electrochemical reactions occur with the decrease in the frequency, and the atomic oxygen electrolyzed dissolves in the molten metal pool; the nonmetallic inclusions, which are distributed dispersively in the ingot, have an increased content, and their size is approximately in the range of 2-3 μm.     

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.     

Synthesis of Spherical (Y,Gd)BO3∶Eu3+ Phosphor Using W/O Emulsion System

Spherical (Y, Gd)BO3:Eu3 phosphor particles with a narrow size distribution(2～4 μm) was obtained by firing the Y-Gd-Eu-BO3 precursor prepared in a W/O style emulsion system. In the W/O emulsion system, kerosene, used as oil phase, was mixed with Span 80 and Tween 80 compounds which were employed as the emulsifier with an HLB (hydrophile-lipophile balance) value of 5.2～5.3. Both rare earths (Y, Gd and Eu) nitrate and boric acid solution or ammonia solution were used as aqueous phase. The synthesis conditions, such as emulsion composition, emulsifying style, precipitation reaction process, reaction temperature, morphology control, and so on, were investigated, and the optimum synthesis conditions for preparing spherical (Y, Gd)BO3∶Eu3 phosphor was obtained. The phosphor was characterized by XRD, SEM, laser particle size analysis, emission and excitation spectrum under vacuum ultraviolet (VUV), and so on. The phosphor synthesized using the water-in-oil emulsion method with median diameter (D50) of 2～4 μm shows agreeable photoluminescence (PL) property and sphericity. The main emission peak appears at about 593 nm, which corresponds to 5D0→7F1 transition (magnetic-dipole transition) of the Eu3 ion. The cell parameters and powder diffraction data were indexed. The structure of the phosphor belongs to the hexagonal system with space group P63/m.     

Effect of scandia on tungsten oxide powder reduction process

Scandia doped tungsten powders were prepared by spray drying combined with two-step hydrogen reduction.The particle size of doped tungsten powder,powder morphology and doped tungsten matrix were characterized by scanning electron microscope,X-ray diffrac-tion and laser diffraction particle size analyzer,respectively.The reduction behavior of Sc2O3 doped tungsten oxide and the effect of Sc2O3 on the property of tungsten powder were studied by the temperature programmed reduction.The experimental results showed that the pre-cursor powders prepared by spray drying had spherical shape.The addition of Sc2O3 could decrease the reduction temperature of tungsten oxide.The scandia doped tungsten powder had sub-micrometer size in the range of 0.1 to1 μm and scandium distributed evenly in the powder.By using this kind powder,sub-microstructure cathode matrices with semispherical grains and homogenous distribution of scan-dium were obtained.     

Photoluminescence enhancement of YAG：Ce~（3＋） phosphor prepared by co-precipitation-rheological phase method

YAG:Ce3+ phosphor was prepared by a novel co-precipitation-rheological phase method.The resulting YAG:Ce3+ phosphor was characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM) and photoluminescent emission spectra.By using acetic acid as solvent,YAG:Ce3+ powder with small particle size(≤2 μm) was obtained at a relatively lower sintering temperature of 1400 oC.With the content of acetic acid increasing,small particles dissolved and disappeared,but larger particles grew up and changed its shape from spherical to partially rectangular.Meanwhile,the emission intensity of the sample prepared by co-precipitation-rheological phase method was about 43% higher than that of the sample prepared by co-precipitation method.It was assumed that the significant improvement of luminescence was mainly because the rheological phase presented a better diffusion environment,and therefore,a better homogeneity of activators of Ce3+.     

Preparation and Luminescent Properties of GdMgB5O10 Doped with Ce^3＋ or／and Tb^3＋ by sol-Gel Method

Ce^3 or/and Tb^3 doped GdMgB5O10 phosphors were prepared by sol-gel technique. XRD, SEM and PL (photolumineseent) measurements were used to characterize the phosphor powders. The results of XRD reveal that phase pure GdMgB5O10 powders are formed at 800℃ and conform the good quality of the synthesized materials obtained by such a process. The luminescent properties of GdMgB5O10:Ce^3 and/or Tb^3 are presented. Their luminescent mechanism and host-to-activator energy transfer were discussed.     

Review on Rare Earth／Polymer Composite

The epecial properties of rare earth/polymer composite were described.More emphasis was put on the radiation shielding and magnetic properties,In the application to X-ray shielding,rare earth/polymer composite can make up the feeble absorbing area.If the rare earth content is high enough,it can demonstrate strong ability for thermal neutron absorption,The composite has strong paramagnetism.The feasibility of preparing magnetic rare earth/polymer compostite was discussed,In addition,three preparation methods were introducde:simlle polymerization,mixing and reaction processing,The effect of the rare earth/polymer composties pre-sturcture and the coordinate number of rare eatrh ions on the light property was analyzed,Rare earth/polmer compostie may have the structure and property simlar to those of the ionomer,The feasibility of the in-situ preparation of the rare earth/polymer nano structure is indicated ,Besides,the relationship between struchture and properties of the rare earth/polymer composite was discussed,The problems associated with such composite materials were also presented.     

Synthesis of high quality Ce:YAG nanopowders by graphene oxide nanosheet-assisted co-precipitation method

(Ce_(0.04)Y_(2.96))Al_5O_(12) phosphor nanoparticles were prepared by a modified co-precipitation method with graphene oxide(GO) nanosheets used as dispersing agent. The GO concentration is controlled at 0.0.005,0.01, 0.02, and 0.03 g/L. The addition of lamellar GO nanosheets in the precipitant solution possibly enhances both the dispersity of precursor particles and the crystallinity of phosphor nanoparticles. Pure Ce-doped YAG phase is obtained by calcining the precipitate at 1000 ℃ for 3 h. The(Ce_(0.04)Y_(2.96))Al_5 O_(12)phosphor nanoparticles have an average size of 64 nm and there is no significant change on particle size with increase of the GO concentration in precipitant solution. The luminescence property of(Ce_(0.04)Y_(2.96))Al_5O_(12) phosphor nanoparticles varies with different concentrations of GO. The photoluminescence emission intensity of the optimum sample with 0.02 g/L GO is about 1.6 times higher than the sample without using GO.