Synthesis and Spectral Properties of Nd^3＋： Gd3Ga5O12 Nanopowder for Transparent Laser Ceramics

Nd^3＋： Gd3Ga5O12（Nd ： GGG） nanopowder for transparent laser ceramics was synthesized using sol-gel method. XRD, SEM, and fluorescence spectrum were used to study the properties of Nd^3＋ ：Gd3Ga5O12 nanopowder. XRD patterns of samples show that it has a cubic structure. Meanwhile, pure Nd：GGG crystals were obtained at 1000 ℃ for 12 h. SEM photographs show that dispersed, uniform, ball-like Nd：GGG nanopowder is obtained. Both XRD and SEM results show that the crystallization degree and the grain size increase with the increase in calcining temperature. Analysis of fluorescence spectrum shows that fluorescence emission occurs at 1062.7 nm, which is the result of Nd^3＋ （^4F3/2→^4I11/2） transition. Homogenous Nd ： GGG nanopewder with a small grain size synthesized using the sol-gel method is favorable for sintering the transparent ceramic, which proves that the nanopewder obtained is suitable as a precursor for preparing GGG transparent ceramics.     

Microwave gel combustion synthesis and sinterability of Nd：GGG nanopowders

Neodymium doped gadolinium gallium oxide （Nd：GGG） nanopowders synthesized by microwave gel combustion using alanine as a fuel was reported. Metal nitrates solution with alanine fuel was combusted in microwave to give precursor. The micro-wave precursor powder was calcined at different temperatures from 800 to 1100 ℃. Phase pure Nd：GGG formation took place at 800 to 1100 ℃ as observed by X-ray diffraction （XRD） and Fourier transform infra-red （FTIR） spectroscopy. However particle size in-creased with calcinations temperature from 25 nm at 800 ℃ to 200 nm at 1100 ℃.Nd：GGG nanopowder obtained at different calci-nation temperatures were compacted and sintered at 1550 ℃ for 3 h in air. Most densified ceramic was obtained from Nd：GGG nanopowder calcined at 1100 ℃. Microstructure as observed from scanning electron microscopy （SEM） showed that the most densi-fied ceramic, obtained from nanopowder calcined at a higher calcination temperature, had a more uniform grain-size distribution, fewer pores and greater densification. XRD of sintered sample showed retention of phase purity.     

Effects of Nd, Sm, Gd, Dy, Er Dopant on Electrical Properties of BaTiO3 Ceramics

BaTiO3 ceramics doped with various quantities of Nd2O3, Sm2O3, Gd2O3, Dy2O3 and Er2O3 were prepared respectively ( the adulterate concentrations were 0. 001,0. 002, 0. 003, 0.005, 0. 007 mol fraction) through a sol-gel method and their electrical properties were researched. It is found that each adulteration of Nd2O3, Sm2O3 Gd2O3,Dy2O3 and Er2O3 all can make the resistivity of BaTiO3 ceramics decline , especially Sm2O3 and Gd2O3. When the addition of Sm2O3 is 0. 001 mol, the resistivity is the smallest, declining from 4.0 × 1012 to 6.5 × 103 Ω different kind of rare earth exhibits different regularity. The grain resistance of BaTiO3 ceramics doped with Sm2O3 or Gd2O3 exhibits a NTC effect, at the same time the grain boundary resistance has a PTC effect, and the grain boundary resistance is much larger than the grain resistance, so the PTC effects of BaTiO3 ceramics doped with Sm2O3 or Gd2O3 originate from the grain boundary. The additions of Nd2O3 , Gd2O3 or Er2O3 make the dielectric constant and the dielectric loss of BaTiO3 ceramics change evidently, especially Nd2O3. The dielectric constant is larger than that of pure BaTiO3 ceramics, on the other hand, the dielectric loss is much lower, which is useful in capacitor fields.     

Single step low temperature synthesis of gadolinium gallium garnet nanopowders

Solution combustion synthesis of single-phase gadolinium gallium oxide(Gd3Ga5O12,GGG)nanopowders,by a fuel mixture approach using urea and glycine at a low temperature of 500oC,was being reported for the first time.Based on the fact that urea and glycine are good fuels for gallium oxide and gadolinium oxide synthesis,the fuel mixture composition was obtained,which could lead to direct phase pure cubic Gd3Ga5O12 formation without any subsequent calcination step.Combustion was carried out in furnace pre-heated at 500oC.Thermogravimetric analysis(TGA)of combustion product showed negligible mass loss indicating direct formation of GGG powder.Fourier transform infrared(FTIR)spectrum of combusted product showed peak characteristic of GGG in case of mixed fuel.X-ray diffraction(XRD)confirmed formation of phase pure GGG at 500°C in preheated furnace.Very fine,well dispersed nanometric particles of size range of 50-100 nm were obtained,being uniform and close to spherical morphology as observed by transmission electron microscope(TEM).     

Synthesis of La3+ and Nd3+ co-doped yttria nanopowder for transparent ceramics by oxalate precipitation method

Polycrystalline Nd3+ and La3+ co-doped yttria nanopowder Nd3+:Y1.90La0.10O3 for transparent ceramics was synthesized by co-precipitation method using oxalate acid as the precipitant and(NH4)2SO4 as the electrical stabilizer under ultrasonic radiation.Nanopowders calcined at different temperatures were characterized with thermal gravimetric-differential thermal analysis(TG/DTA),X-ray diffraction(XRD),transmitting electron microscopy(TEM),energy dispersive spectrometry(EDS) and spectral analysis techniques.Th...     

Synthesis and Luminescence Properties of Gd_2O_3∶Eu~(3+) Phosphors

Gd2 O3∶Eu3+ isanefficientredemittinglumines centmaterial ,whichcanbeappliedindisplays[1,2 ] .TheconventionalcommercialGd2 O3∶Eu3+ ismainlysynthesizedbyhightemperaturesolid statereactionandchemicalco precipitationmethods .Anadvancedperformanceofdisplaysrequireshighqualityphospho rssuchashighbrightnessandefficiency ,monodisper sityandfinegrainsize .Muchresearchhasanticipatedthatsubmicrometer sizedandnanometerluminescentmaterialswillhavethesepotentialadvantages[3～ 8] ,sosubmicrometer sizedan…     

Nanostructured Yb：GGG polycrystalline powders via gel combustion method

Gadolinium gallium garnet (GGG) nanopowders doped with ytterbium ions (Yb:GGG) were synthesized with citric acid as a fuel via gel combustion method. The optimized conditions for preparing Yb3+:Gd3Ga5O12 nanopowders were discussed. The heat behavior, struc-ture and morphology of powders were analyzed with thermal analysis (TG-DTA), X-ray diffraction (XRD), infrared spectra (IR) and trans-mission electron microscope (TEM). TG-DTA analysis revealed that the weight loss of the precursor occured below 800 ℃ and its crystalli-zation temperature was 830.6 ℃. XRD and IR analysis showed that the precursor converted directly into pure GGG at a relatively lower tem-perature (900 ℃) without any other intermediate phase. The lattice constant was 1.2377 calculated by extrapolation method. TEM results in-dicated that the spherical powders showed good dispersity and had a relatively narrow size distribution with average particle size of approxi-mately 40-50 nm, which was favorable for good sinterability of Yb:GCG laser ceramic.     

Fabrication and Luminescence Properties of Ca2Gd8(SiO4)6O2:Er3+ Phosphors via Sol-Gel Process

Ca2RE8(SiO4)6O2 (RE=Y, Gd, La) is a kind of ternary rare-earth-metal silicate with the oxyapatite structure, which was used as host materials for the luminescence of various rare earth and mercury-like ions. Ca2Gd8(SiO4)6O2:Er3 phosphors were prepared through the sol-gel process. X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectra were used to characterize the resulting phosphors. The results of XRD indicate that the phosphors crystallized completely at 1000 ℃. SEM study reveals that the average grain size is 400～1000 nm. In Ca2Gd8(SiO4)6O2:Er3 phosphors, the Er3 shows its characteristic green emission at 528 nm (2H11/2-4I15/2) and 548 nm(4S3/2-4I15/2) upon excitation into 382 nm, with an optimum doping concentration of 5% (mole fraction) of Gd3 in the host lattices.     

Lattice Parameter Change of Nd∶Gd3Ga5O12 Crystal with Growth Direction

The lattice parameter change of Nd∶GGG crystal was studied by X-ray powder diffraction and the least square fitting method. The results indicate that the lattice parameters of Nd∶GGG increase along the crystal growth direction. By analyzing the Nd∶GGG crystal structure and ions occupying site, the reason of lattice parameter change is mainly attributed to the volatilization of gallium ingredient and lead to the Ga vacancy sites(Oxygen octahedral center) were occupied by Gd3 with large ionic radii, and that the substitute increases with the crystal growth direction. In addition, the Gd sites(oxygen dodecahedron center) were occupied by dopant Nd3 with large ionic radii and the Nd3 distribution coefficient in GGG crystal is smaller than 1, therefore, the substitute also increased with the crystal growth direction, which is another reason led to the lattice parameter increase along the crystal growth direction. In order to decrease the lattice parameter change and improve the crystal quality, some methods were adopted to restrain effectively the Ga2O3 volatilization and decrease the Nd3 concentration change along the crystal growth direction.     

Preparation and Gas－Sensing Properties of NdFeO3 Nanocrystalline

With the Nd2O3, Fe(NO3)3·9H2O, nitric acid(1∶1 vloume fraction) for the starting materials, rare earth composite oxide NdFeO3 with the structure of perovskite type was synthesized by sol-gel method in the system of citric acid. Structural characteristics were characterized by XRD and TEM which indicate that the sample is nanocrystallite with uniform grain size distribution and the a verage grain size is about 28 nm. Moreover, the gas sensing properties of the material were tested. The results show that NdFeO3 sensors have high sensitivity, excellent selectivity and quick response and recovery behavior to H2S, hence, this gas sensing material has a better prospects in industrial practice.     

Effect of Gd2O3 and La2O3 on BaTiO3 -Based Ceramics

The addition of rare-earth oxides Gd2O3 and La2O3 to BaTiO3-based ceramics can restrain the growth of grain size, which obtained small grain size below 1 μm and high density. The dielectric constant at room temperature increased and the curve of ε-T was flattened which illustrated that the ferroelectricity of BaTiO3-based ceramics was weakened. In addition, it is illustrated that Gd2O3 leads to chemical nonhomogeneous property, i.e. core-shell structure and La2 O3 leads to chemical homogenous property, which take different effects on capacitance- temperature characteristic.     

Specific features of Eu~(3+) and Tb~(3+) magnetooptics in gadolinium-gallium garnet (Gd_3Ga_5O_(12))

We reported magnetooptical properties of Eu3+(4f(6)) and Tb3+(4f(8)) in single crystals of Gd3Ga5O12 (GGG), Y3Ga5O12 (YGG), and Eu3+(4f(6)) in Eu3Ga5O12 (EuGG) for both ions occupying sites of D2 symmetry in the garnet structure. Absorption, luminescence, and magnetic circular polarization of luminescence (MCPL) spectra of Tb3+ in GGG and YGG and absorption and magnetic circular dichroism (MCD) of Eu3+ in EuGG were studied. The data were obtained at 85 K and room temperature (RT). Magnetic susceptibility of...     

Preparation and Photocatalytic Activity of Nanocrystalline GdFeO3

Photocatalytic reactions at semiconductor particleshave been the focus of numerous investigations in re-cent years ,since their applicationresults inthe quan-titative degradation of a large number of chemical con-taminants . Of many semiconductor oxides , TiO2hasbeen provento be the benchmark photocatalyst for ef-fective degradation of organic pollutants ,pri marily be-cause of its optical and electronic properties ,lowcost ,chemical stability and non-toxicity .However ,sinceitsband-gapis larg…     

Preparation of Neodymium-Doped Yttrium Aluminum Garnet Transparent Ceramics by Homogeneous Precipitation Method

Neodymium-doped yttriumaluminumgarnet(Nd∶YAG)transparent polycrystalline ceramics,laser ce-ramic matrix materials,are gradually becomingsubsti-tutes for single crystals because they are provided withpredominantly chemical stability,highly doped ionconcentration,excellent optical performance and hightemperature stability[1,2].Presently,the conventionallyused methods to produce Nd∶YAG powders are solid-state processes[3],chemical precipitation methods[4,5]andlowtemperature combustiontechniqu…     

Luminescence and Energy Transfer Properties of Ca2Gd8(SiO4)6O2∶ A (A=Pb2+,Tm3+)Phosphors

Ca2Gd8(SiO4)6O2∶ A(A=Pb2 , Tm3 )phosphors were prepared through the sol-gel process. X-ray diffraction(XRD), scanning electron microscopy(SEM)and photoluminescence spectra were used to characterize the resulting phosphors. The results of XRD indicate that the phosphors crystallized completely at 1000 ℃. SEM study reveals that the average grain size is 300～1000 nm. In Ca2Gd8(SiO4)6O2∶ Tm3 phosphors, the Tm3 shows its characteristic blue emission at 456 nm(1D2-3F4)upon excitation into its 3H6 - 1D2(361 nm), with an optimum doping concentration of 1mol% of Gd3 in the host lattices. In Ca2Gd8(SiO4)6O2∶ Pb2 , Tm3 phosphors, excitation into the Pb2 at 266 nm(1S0-3P1)yields the emissions of Gd3 at 311 nm(6P-8S)and Tm3 at 367 nm(1D2 -3H6)and 456 nm(1D2-3F4), indicating that energy transfer processes of Pb2 - Gd3 and Pb2 - Tm3 have occurred in the host lattices.     

Rare earth doped CaCu_3Ti_4O_(12) electronic ceramics for high frequency applications

Ca1-xRxCu3Ti4O12(R=La,Y,Gd;x=0,0.1,0.2,0.3) electronic ceramics were fabricated by conventional solid-state reaction method.The microstructure and dielectric properties as well as impedance behavior were carefully investigated.XRD results showed that the secondary phases with the general formula R2Ti2O7 existed at grain boundaries of rare earth doped ceramics,which inhibited abnormal grain growth.The dielectric constant decreased from 4×105 in pure CaCu3Ti4O12(CCTO) ceramics to 2×103 with rare earth doping.However,all samples showed high dielectric constant in broad frequency range(10 MHz).The cutoff frequency(f0) was remarkably shifted to higher frequency from 13 MHz(pure CCTO ceramics) to 80 MHz(Gd-doped CCTO ceramics).Meanwhile,the dielectric loss tangent rapidly decreased approximately 10 times.These improvements of dielectric properties by rare earth doping are very useful in wide frequency chip capacitor and LTCC devices.     

铽在硫氧化镧基质中的光致发光

采用高温固相反应法制备了La2O2S∶Tb3+、La2O2S∶Tb3+,RE3+(RE=Dy,Gd,Ce,Sm)荧光粉样品并进行了相关表征。结果表明,合成样品的晶体结构与La2O2S相同,为六方晶系;荧光粉颗粒的形貌多为长方形片状;发射光谱由494 nm、545 nm、587 nm、622 nm的一系列锐发射峰组成。研究发现Tb3+的掺杂浓度对样品主发射峰545 nm的发光强度影响很大,且在摩尔分数x(Tb3+)=0.02时达到最强。稀土离子Dy3+、Gd3+对La2O2S∶Tb3+荧光粉的发光有明显的敏化作用。     

Preparation and Ionic Conductivity of Ultrafine Li2+xRExSi1-xO3 by Sol-Gel Method

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氧化钆对钛酸钡陶瓷结构和介电性能的影响

采用固相法制备得到了掺杂 1% (mol) Gd2 O3的钛酸钡陶瓷 ,并通过 X射线衍射分析和扫描电镜对其结构进行了表征。对其介电常数、介电损耗和室温电阻率进行了测定 ,结果表明 Gd2 O3掺杂 Ba Ti O3陶瓷的介电常数明显增加 ,介电损耗也有所升高 ,室温电阻率明显降低     

Sm~(3+)掺杂ZnO-SiO_2-B_2O_3系微晶玻璃的制备及发光性能的研究

通过高温熔融法制备了ZnO-SiO2-B2O3:Sm3+系微晶玻璃,并采用SEM、XRD及荧光光谱仪研究了该微晶玻璃的析晶过程及发光性能。结果表明,该微晶玻璃的主晶相为尖晶石(ZnAl2O4),被紫外光激发能够发出红色光;晶化时间的改变导致了尖晶石的逐渐析出,改变了光谱谱线的强度但不改变谱线的位置。Sm3+最佳掺杂摩尔分数为0.4%。