Preparation and characterization of Y3Al5O12:Ln（Ln=Eu,Ce） phosphor powders by ultrasonic atomization and co-precipitation process

A novel technique for YAG:Ln(Ln=Eu,Ce) phosphor powder synthesis with a nanocrystalline structure was developed.Nanocrystalline YAG:Ln powder was prepared by an ultrasonic atomization and co-precipitation method using a mixture solution of ammonium hydroxide(NH3·H2O) and ammonium hydrogen carbonate(NH4HCO3) as precipitant.The as-prepared nano-powders were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),and fluorescence spectrometer.The obtained phosphor powders were homogenous and in size of 50-70 nm.The results demonstrated that by using ultrasonic atomization and co-precipitation process,we could synthesize a good quality YAG:Ln(Ln=Eu,Ce) phosphor powder that had many potential applications.     

Synthesis and characterization of YAG: Ce3+ fluorescence powders by co-precipitation method

YAG:Ce³⁺(Yttrium aluminum garnet) fluorescence powders were successfully prepared by co-precipitation method using aluminum nitrate, yttrium nitrate, cerous nitrate as the starting materials and ammonium carbonate as precipitant. The products were characterized by X-ray powder diffraction, luminescence spectrometer, transmission electron microscope (TEM). The XRD results showed that the obtained YAG:Ce³⁺ fluorescence powders had the crystalline structures of YAG at calcinations temperature of 900 °C and the TEM results showed that the grain diameters were about 100 nm. The YAG:Ce³⁺ fluorescence powders, synthesized by co-precipitation method, had the best luminescence property when the Ce doping amount was x=0.06 in the molecular formula of Y_3-xCe_xAl₅O₁₂, the calcinations time was 2 h and the calcinations temperature was 1000 °C.     

Synthesis and characterization of YAG:Ce³⁺ fluorescence powders by co-precipitation method

YAG:Ce3+(Yttrium aluminum garnet) fluorescence powders were successfully prepared by co-precipitation method using aluminum nitrate,yttrium nitrate,cerous nitrate as the starting materials and ammonium carbonate as precipitant.The products were characterized by X-ray powder diffraction,luminescence spectrometer,transmission electron microscope(TEM).The XRD results showed that the obtained YAG:Ce3+ fluorescence powders had the crystalline structures of YAG at calcinations temperature of 900 oC and the TEM results showed that the grain diameters were about 100 nm.The YAG:Ce3+ fluorescence powders,synthesized by co-precipitation method,had the best luminescence property when the Ce doping amount was x=0.06 in the molecular formula of Y3-xCexAl5O12,the calcinations time was 2 h and the calcinations temperature was 1000 °C.     

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+.     

Study on co-precipitation synthesized Y3Al5O12:Ce yellow phosphor for white LED

A precursor of the Y3Al5O12:Ce (YAG:Ce) phosphor was obtained by co-precipitation of the solution of high purity nitrates with ammonium bicarbonate solution. The precipitation process of the precursor was studied in this work. YAG:Ce yellow phosphors with fine morphology was synthesized by annealing the precursor at a reducing atmosphere. The crystal phase, microstructure of the phosphors and their photoluminescence were investigated. The results indicated that the pure phase of YAG:Ce could be obtained at ...     

Optical characteristics of Ce,Eu:YAG single crystal grown by Czochralski method

Eu-doped Ce:YAG single crystal (SC) was fabricated by the Czochralski method. The crystal structure, optical and photoelectric property of the constructed w-LED was investigated. The XRD and HRTEM results show that YAG crystal structure has little change when Eu³⁺, Ce³⁺ are doped. Absorption spectra and photoluminescence spectra show that the Ce,Eu:YAG single crystal can effectively absorb the 460 nm blue light to form a broadband emission center at 530 nm, decay curves of the crystal show that the energy transfer between Ce³⁺ and Eu³⁺ is highly suppressed. Compared with commercial Ce:YAG phosphor, Ce,Eu:YAG exhibits better thermal stability.     

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.     

共沉淀法制备稀土石榴石Ln3Al5O12(Ln=Y, Ce, Yb)

以Y2O3、Yb2O3、Al(NO3)3.9H2O和Ce(NO3)3.6H2O为原料,NH4HCO3、NH3.H2O做复合沉淀剂,用共沉淀法制备纳米稀土石榴石Ln3Al5O12(LnAG,Ln=Y,Ce,Yb)粉体。用TG/DTA、XRD、SEM、TEM等手段对LnAG前驱体及煅烧后的粉体进行表征。结果表明,用上述方法在1 000℃煅烧3h可得到分散性好、形状规则且粒径为50nm左右的Y3Al5O12、Yb3Al5O12、Y2.9Ce0.1Al5O12石榴石粉体,但不能得到Ce3Al5O12石榴石,合成石榴石粉体的最佳煅烧温度为1 050℃以上。     

Combustion synthesis and luminescence properties of blue NaBaPO4:Eu2+ phosphor

The blue-emitting phosphor NaBaPO4:Eu2+ was prepared by the combustion method. The phase structure and microstructure of the as-prepared samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Under the excita-tion wavelength of 360 nm, the emission spectrum exhibited only one blue band centering at 435 nm, which was ascribed to the 4f65d1→4f7 transition on Eu2+ ions. Compared with the phosphor obtained by solid-state reaction method, the relative emission intensity of sample ob-tained by combustion method increased slightly. The decay times and the temperature dependence luminescence intensities (25-300 oC) were discussed in order to further investigate the potential applications. Furthermore, Eu2+-doped NaBaPO4 phosphor showed higher thermally sta-ble luminescence comparable to commercially available Y3Al5O12:Ce3+ (YAG:Ce3+) phosphor. All the investigated suggestions that Na-BaPO4:Eu2+ is a good phosphor candidate applied in white light emitting diode.     

Luminescence modification of Eu3+-activated molybdate phosphor prepared via co-precipitation

Eu-activated CaMoO4 phosphors were co-precipitated in an aqueous solution, and NH3·H2O, NH4HCO3 and (NH2)2CO as pre-cipitating aid agents were compared based on the morphology and particle size distribution of the phosphor samples. Sm3+ as sensitizer ion was investigated on the luminescence of CaMoO4:Eu, and it could strengthen the 406 nm absorption of this phosphor. At last, the scheelite CaMoO4:Eu and wolframite ZnMoO4:Eu were selected to compare their host absorption. The result showed that the scheelite molybdate host exhibited stronger UV absorption than wolframite one.     

Influence of ammonium sulfate on YAG nanopowders and Yb:YAG ceramics synthesized by a novel homogeneous co-precipitation method

Homogeneous and dispersed Y_3 Al_5 O_(12)(yttrium aluminum garnet,YAG) nanopowders were synthesized via a homogeneous co-precipitation method from the mixed solutions of yttrium nitrate,aluminum nitrate and a small amount of ammonium sulfate using hot urea as the precipitant.The method has the superiorities that co-precipitation of cations is ensured and continuous decomposition of the hot urea is achieved to obtain the narrow size distribution particles.The addition of small amount of ammonium sulfate surfactant,although has no influence on YAG garnet phase formation,has significant effect on dispersion,particles distribution and sinterability of the resultant YAG and Yb:YAG powders.Compared with the undoped sample,the green body of Yb:YAG doped with ammonium sulfate has higher total shrinkage,linear shrinkage rate and relative density through sintering at 1600 ℃.The resultant Yb:YAG powders can be sintered into transparent ceramics at 1700 ℃ through vacuum sintering.The influence of the sulfate ions on characteristics of the resultant powders was thoroughly studied.     

Raman spectroscopy study of the phase transitions in rare-earth metal trichlorides

The structures of crystalline (over a wide temperature range) and molten rare-earth metal-LnCl₃ (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy) trichlorides are comprehensively studied by Raman spectroscopy.     

沉淀温度对制备铈掺杂YAG粉体的影响

文中采用共沉淀法来制备铈掺杂YAG前驱体.为获得纯相YAG:Ce3+粉体,实验以CeO₂、Y₂O₃、Al(NO₃)₃·9H₂O和NH₄HCO₃为原料,在不同的沉淀温度下来制备YAG:Ce3+前驱体,将所制得的前驱体经高温煅烧还原得到YAG:Ce3+粉体,并通过TG/DTA、XRD及光谱分析等手段分析了沉淀温度对YAG:Ce3+粉体性能的影响.实验结果表明:沉淀温度为25 ℃时制备出来的YAG:Ce3+粉体发光强度好.      

Citrate sol-gel combustion preparation and photoluminescence properties of YAG:Ce phosphors

Yellow-emitting YAG:Ce3+ nanocrystalline phosphors were prepared by citrate sol-gel combustion method using citric acid as the fuel and chelating agent. The influence of mole ratio of citric acid to metallic ions (MRCM), pH value of the solution, calcination temperature and Ce-doped concentration on the structures and properties of as-prepared powders were investigated in detail. Higher crystallinity and better luminescence performance powders were obtained at MRCM=2, pH=3 and the calcination temperature of 1200 °C. The phosphors exhibited the characteristic broadband visible luminescence of YAG:Ce. The optimum concentration of Ce3+ was 1.0 mol.%, and the concentration quenching was derived from the reciprocity between electric dipole and electric quadrupole (d-q). Especially, the pH value of the solution was a key factor to obtain a stable sol-gel system and then obtain pure and homogeneous rare earth ions doped YAG phosphors at a lower tem-perature. The Y3Al5O12:Ce0.03 phosphor with optimized synthesis-condition and composition had a similar luminescence intensity with the commercial phosphor YAG:Ce.     

Luminescence of Eu^3 ＋ in LnAlO3 （Ln = Gd, Y） under UV and VUV Excitation

Single phases of LnAlO3 : Eu^3 ( Ln = Gd, Y ) were obtained by the process of evaporation of their nitric acid solution, and then pyrolysis of their nitrate salts. On monitoring by 613 nm emission, broad bands at around 270 and 170nm were observed in the excitation spectrum of Gd0.95Eu0.05AlO3. These peaks could be assigned to charge transfer (CT)transitions of Eu^3 -O^2- and Gd^3 -O^2- respectively. All the transitions observed in Gd0.95Eu0.05AlO3 are faithfully reproduced in the Y0.95Eu0.05AlO3, but with an exception of the ^8S7/2→^6I11/2 transition of Gd^3 . The 153 nm broad band could be the CT transition of Y^3 -O^2 - . Accordingly, the efficiency luminescence of (Gd, Y) BO3 : Eu^3 was explained as a result of CT transitions of Gd^3 -O^2- and Y^3 -O^2- under 147 nm excitation. Under VUV excitation, Gd0.95Eu0.05AlO3 exhibits a bright red luminescence with CIE chromaticity coordinates of (0.623, 0. 335) with a PL intensity of 30 of the commercial phosphor (Gd, Y) BO3 : Eu^3 (KX-504A). The PL spectrum of Y0.95Eu0.05AlO3 is similar to that of Gd0.95Eu0.05AlO3. Calculation of the color coordinates gives x = 0. 636, y = 0. 340 with a PL intensity of 50 of the (Gd, Y) BO3 : Eu^3 ( KX-504A) for Y0.95Eu0.05AlO3, and confirms that it has the appearance of pure spectral red, corresponding approximately to 608 nm. It can be concluded that LnAlO3:Eu^3 is a promising red VUV phosphor.     

Study on photodegradation of Azo dye by polyoxometalates/polyvinyl alcohol

A series of photocatalysts, K11[Ln(PW11O39)2]/PVA (Ln=La, Ce, Pr, Nd, Sm) were prepared by K11[Ln(PW11O39)2] (Ln=La, Ce, Pr,Nd, Sm) containing five kinds of lanthanides and polyvinyl alcohol as the support. The catalysts obtained were characterized by Fourier trans-form infrared spectra, UV-vis spectra, powder X-ray diffraction, and scanning electron microscopy, indicating that the structure of K11[Ln(PW11O39)2] and polyvinyl alcohol remained intact, respectively. The photocatalysts exhibited efficient catalytic activity to degrade methyl orange, Congo Red, Ponceau 2R. The maximal degradation conversions of the three kinds of dyes were 99.58%, 47.61%, 72.42%, respectively.     

Microwave assisted synthesis,spectroscopic, thermal,and antifungal studies of some lanthanide（Ⅲ） complexes with a heterocyclic bishydrazone

A bishydrazone formed by the condensation of isatinmonohydrazone and salicylaldehyde reacted with lanthanide（Ⅲ） chloride to form complexes of the type [Ln（HISA）2Cl3], where, Ln=La（Ⅲ）, Ce（Ⅲ）, Pr（Ⅲ）, Nd（Ⅲ）, Sm（Ⅲ）, Eu（Ⅲ）, or Gd（Ⅲ） and HISA= [（2-hydroxybenzaldehyde）-3-isatin]bishydrazone. Both reactions were carried out under microwave conditions. The ligand and the metal complexes were characterized on the basis of elemental analysis, molar conductance, magnetic susceptibility measurements, UV visible, infrared, far infrared, and proton NMR spectral data. The ligand acted as neutral tridentate, coordinating through the carbonyl oxygen, azomethine nitrogen, and phenolic oxygen without deprotonation. The ligand and lanthanum（Ⅲ） complex were subjected to X-ray diffraction studies. The X-ray diffraction pattern of ligand exhibited its crystalline nature and that of the lanthanum（Ⅲ） complex indicated its amorphous character. The thermal decomposition behaviour of the complex, [La（HISA）2Cl3], was examined in the temperature range of 40-800 ℃ using TG, DTG, and DTA. The ligand and the metal complexes were screened for their antifungal activities.     

Thermodynamics of mixed oxide compounds, Li2O · Ln2O3 (Ln=Nd or Ce)

The thermodynamics of mixed oxide compounds of the type Li₂O · Ln₂O₃ (Ln=Nd or Ce) has been studied by measuring the lanthanide content of molten LiCl-Li₂O-Li solutions in equilibrium with the solid mixed oxide compound at 923 K. The observed total lanthanide mole fraction in the molten salt when in equilibrium with both solid Ln₂O₃ and LiLnO₂ was found to be 1.0×10⁻⁴ and 5.9×10⁻⁴ for Ln=Nd and Ce, respectively. The calculated mole fractions of LiLnO₂ in the molten salt when the solid mixed oxide compound was present are 2.6×10⁻⁵ and 2.1×10⁻⁴ for LiNdO₂ and LiCeO₂, respectively. The unexpectedly large “solubilities” of the sesquioxides in the presence of Li₂O can be explained by the formation of complex oxide species, LiLnO₂ and Li₃LnO₃, in the molten salt solutions. The equilibrium constants and the free energies of formation for these species were derived from the measured data. The free energies of formation of the solid mixed oxide compounds at 923 K were found to be −1014±1.5 kJ/mol for LiNdO₂ and −1006±11.0 kJ/mol for LiCeO₂.     

Preparation and luminescent properties of CaF2:Ln3+ (Ln:Er,Er/Yb)/Nafion composite films

In this work, CaF_2:Ln~(3+)(Ln:Er,Er/Yb)/Nafion composite films were prepared using Nafion as modifications and matrices by dripping method. The composite films were characterized by Fourier transform infrared spectroscopy(FT-IR), X-ray diffraction(XRD) and scanning electron microscopy(SEM). Composite films are transparent and CaF_2:Ln~(3+)(Ln:Er,Er/Yb) nanoparticles are well dispersed in Nafion films.The thicknesses of CaF_2:Er~(3+)/Nafion and CaF_2:Er~(3+),Yb~(3+)/Nafion composite film are about 77 and 73 μm,respectively. The nanoparticles in composite film possess cubic phase. CaF_2:Er~(3+),Yb~(3+)/Nafion composite film has stronger characteristic emission of Er~(3+) around 1530 nm with full width at half-maximum(FWHM) of 73 nm and longer luminescence lifetimes of 22.04 μs(25.03%) and 100.77 μs(74.97%).     

Insertion Reactions of PhEtCCO and PhNCO into Ln-S （Ln = Er, Y, Yb） Bond of [Cp2Ln（μ-SEt） ]2

The reactivity of lanthanocene thiolates [Cp2Ln（μ-SEt）]2（Ln = Er, Y, Yb） with PhEtCCO and with PhNCO was examined. Treatment of [ Cp2Ln（μ-SEt）]2 with PhEtCCO gives the α-thiolate-substituted enolate complexes [ Cp2Ln （μ-η^1 ：η^3-OC（SEt）CPhEt）]2（Ln = Yb, Y）, while [Cp2Ln（μ-SEt）]2 react with PhNCO to give the lanthanocene amido derivatives [Cp2Ln（OC（SEt）NPh ）]2（Ln = Er, Yb）. In both cases, the insertion reaction is independent of the stoichiometric ratio and the nature of lanthanides, demonstrating that lanthanocene thiolates are high reactive toward PhEtCCO and PhNCO under the conditions involved. All complexes are characterized by elemental analysis and spectroscopic properties, of which the structures of ytterbium enolate and erbium amido are also determined by X-ray single crystal diffraction analysis, indicating that both of them are centrosymmetric binuclear structures.