Sintering of transparent Nd:YAG ceramics in oxygen atmosphere

Yttrium aluminum garnet (YAG) transparent ceramics were fabricated by sintering at oxygen atmosphere. Tetraethyl orthosilicate (TEOS) was added as the sintering additive to control the grain growth and densification. Pores were eliminated clearly at temperature lower than 1700oC, while grain size was around 3 μm. The in-line transmittance was 80% at 1064 nm when samples were sintered at 1710oC. The effect of TEOS was studied in oxygen atmosphere sintering for Nd:YAG transparent ceramics. At higher temperature like 1710oC, the grain growth mechanism was solute drag, while at 1630 and 1550 oC the grain growth was controlled by liquid phase sintering mechanism. And 0.5 wt.% TEOS was the best adding content for Nd:YAG sintered in oxygen atmosphere.     

Synthesis and properties of Yb:Sc_2O_3 transparent ceramics

Yb:Sc2O3 transparent ceramics were fabricated by solid-state reaction and vacuum sintering method.CaO was added as sinteringaids by a high energy ball milling.Transparent nearly-fully dense samples were obtained after 1840 oC sintering.Using transmitted-light microscopewe get the grain sizes are more than 100 μm.Using spectrophotometer we get the absorption coefficient centered at 975 nm was 2.65 cm-1.The phosphorescence spectra showed that the line-widths(FWHM) at 975 and 1041 nm were about 4 and 10 nm and the lifetime of Yb ionsin Sc2O3 transparent ceramics was about 883 μs.According to the absorption and fluorescence band centers of Yb:Sc2O3 transparent ceramics,the level scheme of Yb3+ ions in Sc2O3 ceramics could be gotten.     

Luminescent properties of Ce3+-doped transparent oxyfluoride glass ceramics containing BaGdF5 nanocrystals

The transparent oxyfluoride glass ceramics containing Ba Gd F5 nanocrystals were prepared with a composition of 42 Si O2-12Na2O-16Al2O3-24 Ba F2-4Gd2O3-2Ce F3(mol.%) by thermal treatment technology. The typical DSC curve, X-ray diffraction(XRD) and transmission electron microscopy(TEM) patterns were measured. The transmission spectra and luminescent properties were investigated. The decay times of the Gd3+ ions at 312 nm excited with 275 nm for the Ce3+ ions doped glass and glass ceramics specimens and the energy transfer process between Gd3+ ions and Ce3+ ions were also studied. The XRD analysis and the TEM images confirmed the generation of the spherical Ba Gd F5 nanocrystals. Compared with the PG specimen, the intensity of the luminescence spectra of the glass ceramics specimens was apparently enhanced with the heat treatment temperature increasing, and a blue shift in the excitation spectra and the emission spectra of glass ceramics specimens was obviously observed. In the fluorescence decay curves of the Gd3+ ions, it could be obviously observed that the fluorescent intensity decays in the Ce3+ ions doped glass and glass ceramics specimens decreased rapidly with the increase of the heat treatment temperature. In addition, the energy transfer efficiency from Gd3+ions to Ce3+ ions was also calculated.     

Synthesis and Spectral Properties of Nd3+:Gd3Ga5O12 Nanopowder for Transparent Laser Ceramics

Nd3 :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 Nd3 :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 Nd3 (4F3/2→4I11/2) transition. Homogenous Nd:GGG nanopowder with a small grain size synthesized using the sol-gel method is favorable for sintering the transparent ceramic, which proves that the nanopowder obtained is suitable as a precursor for preparing GGG transparent ceramics.     

Fabrication and long persistent luminescence of Ce3+-Cr3+ co-doped yttrium aluminum gallium garnet transparent ceramics

Persistent luminescence (PersL) materials are widely used in safety indication, traffic and transportation signs, architectural decoration and other fields. In this paper, (Y_1?xCe_x)₃(Al_0.9995Cr_0.0005)₂Ga₃O₁₂ (x = 0.001, 0.002, 0.003, 0.005) transparent ceramics were successfully prepared by solid-state reaction method in air followed by HIP post-treatment. With the increase of Ce³⁺ doping concentration, the optical quality of the as-prepared ceramics is improved and the morphology is denser. Luminescent quenching occurs when the Ce³⁺ concentration is more than 0.2%. The as-prepared transparent ceramics were annealed in different atmospheres. From the PersL decay curves, the transparent ceramics after air annealing show the best PersL performance: luminance with 4424.0 mcd/m² and PersL duration over 865 min after ceasing 365 nm excitation, respectively. The effects of Ce³⁺ doping concentration and annealing atmospheres are also discussed in detail.     

Microstructural characteristics of Nd:YAG powders leading to transparent ceramics

We reported on the successful synthesis of the Nd:YAG (Nd:Y3Al5O12) nano-powders by using urea as the precipitant with the microwave assisted homogeneous precipitation (MAHP) method. The different microstructural characteristics of the Nd:YAG nano-powders were affected by the concentrations of (Y3++Nd3+) and Al3+ ([Y3++Nd3+]=0.06 mol/L, [Al3+]=0.1 mol/L), aging time (6 d) and aging condition (in vessel). The optimum microstructural characteristics of the high quality Nd:YAG nano-powders leading to transparent Nd:YAG ceramics including the pure YAG phase, the smallest crystallite size, a uniform crystallite size distribution, less density defects, uniform micro-components and the proper molar ratio of (Y3++Nd3+) and Al3+ (0.6148) were discussed.     

Preparation and Upconversion Luminescence of Y3Al5O12∶Yb3+, Er3+ Transparent Ceramics

YAG:1% (atom fraction) Yb3 , 0.5% (atom fraction) Er3 transparent ceramics were fabricated by the solid state reaction method using high-purity Y2O3, Al2O3, Yb2O3, and Er2O3 powders as starting materials. The mixed powder compact was sintered at 1760 ℃ for 6 h in vacuum and annealed at 1500 ℃ for 10 h in an air atmosphere. The ceramics consisted of about 10 μm grains and exhibited a pore-free structure. The optical transmittance of the ceramics at 1064 nm was nearly 80%. Upconversion emissions were investigated on the ceramics pumped by a 980 nm continuous wave diode laser, and strong green emission centered at 523 and 559 nm and red emission centered at 669 nm were observed, which originated from the radiative transitions of 2H11/2→4I15/2, 4S3/2→4I15/2, and 4F9/2→4I15/2 of Er3 ions, respectively.     

Fabrication of Transparent Polycrystalline Yttria Ceramics by Combination of SPS and HIP

Transparent polycrystalline yttria is a promising optical ceramics with excellent physical and chemical properties. A commercial yttria powder with a mean particle size of 1.0 μm and narrow size distribution was selected as the starting material. Transparent polycrystalline yttria ceramics without any additives were successfully prepared by hot isostatic pressing (HIP) at 1700 ℃ for 2 h under the pressure of 200 MPa in Ar following spark plasma sintering (SPS). The as-prepared specimens consist of uniform grains of ～40 μm. Scanning electron microscopy (SEM) images show their pore-free structure. The influences of the yttria powder and sintering process on the properties of the yttria ceramics, including the microstructure and optical properties, were further investigated in our study.     

Preparation of transparent Y2O3 ceramic by slip casting and vacuum sintering

In the present work transparent Y2O3 ceramics were made by slip casting and vacuum sintering of nanopowders with sodium poly-acrylic acid(PAA-Na) as dispersant.The rheological properties of Y2O3 nanopowder slurry were investigated using different amounts of dis-persant and solid contents.The microstructures and transmittance of the sintered ceramics were also studied by means of scanning electron microscopy(SEM) and ultra-violet visible spectrometry.The results showed that rheological behaviors of the Y2O3 nanopowder slurry were effectively promoted by sodium polyacrylic acid.Highly dispersive and stable slurries were obtained as the dispersant was added over 1.0 dwb% under the fixed conditions of pH 11 and 45 wt.% solid content.All the slip cast green bodies were sintered into highly dense ceramics after sintering at 1700 oC for 5 h in vacuum,wherein the sample added with 1.1% sodium polyacrylic acid exhibited the highest relative den-sity of 99.36% and transmission of 30% at 800 nm wavelength.     

用于YAG透明陶瓷的喷雾造粒改性粉体的制备

通过喷雾造粒方法对共沉淀合成的纳米粉体进行改性,制备出球形的纳米颗粒.用XRD对粉体进行物相分析;用TEM观察了改性前粉体的颗粒形状、尺寸大小和团聚情况;用SEM观察改性前后粉体的团聚体的颗粒形状、尺寸大小与分散性,以及陶瓷热腐蚀抛光后的表面形貌.结果表明:PVB添加质量分数1.0%为最优添加量;改性后粉体所制素坯的密度显著提高,从而影响陶瓷的致密度和晶界形貌;经真空烧结制备出相对密度达99.95%的无孔净晶界YAG透明陶瓷,陶瓷晶粒的平均尺寸为10μm左右,尺寸分布较均匀,晶界清晰,晶粒中与晶界处较干净,无杂质与气孔的存在.     

Nanocrystals precipitation and up-conversion luminescence in Yb~(3 )-Tm~(3 ) co-doped oxyfluoride glasses

Rare earth ions doped oxyfluoride glass with composition of 28SiO2·22AlO1.5·40PbF2·10PbO·(4.8–x) GdF3·0.1NdF3·xYbF3·0.1TmF3 (x=0, 0.1, 0.2, 0.5, 1, 2, 3, 4 and 4.8) in molar ratio was developed. When the oxyfluoride glasses were heat-treated at the first crystallization temperature, the glasses gave transparent glass-ceramics in which rare earth containing fluorite-type nanocrystals of about 17.2 nm in diame-ter uniformly precipitated in the glass matrix. Compared with the glasses before heat treatment, the glass-ceramics exhibited very strong blue up-conversion luminescence under 800 nm light excitation. Rare earth containing nanocrystals were also space selectively precipitated upon laser irradiation in an oxyfluoride glass, the size of precipitated nanocrystals could be controlled by laser power and scan speed. The intensity of the blue up-conversion luminescence was strongly dependent on the precipitation of β-PbF2 nanocrystal and the YbF3 concentration. The reasons for the highly efficient Tm3 up-conversion luminescence after laser irradiation were discussed.     

Synthesis of ZnO：Dy Nanopowder and Photoluminescence of Dy^3＋ in ZnO

A type of dysprosium-doped ZnO （ZnO：Dy） nanopowder was synthesized by high temperature calcinations. XRD was used to analyze the structure. Photoluminescence spectra were used to study the optical characteristic. PL of ZnO：Dy shows two different spectra which are broad band resulted from the defect of Dy in ZnO and sharp lines from the 4f→4f transition of isolated Dy^3 ＋ luminescence center. The emission and excitation spectra depend on the excitation wavelength and the concentration of Dy^3＋ . The broad bands with peaks at 600 and 760 nm are attributed to the recombination from an electron of the defect Dy in ZnO to a hole in VB.     

Elevating photoluminescence properties of Y3MgAl3SiO12:Ce3+ transparent ceramics for high-power white lighting

Compared with Y₃Al₅O₁₂:Ce³⁺,Y₃MgAl₃SiO₁₂:Ce³⁺(YMASG:Ce³⁺) reveals great potential for highpower white lighting with red-shift spectrum.Herein,YMASG:Ce³⁺ transparent ceramics were explored to be synthesized in the air following hot isostatic pressure(HIP) treatment to obtain tunable and optimized optical properties.Then phase purity,microstructure,transmittance,and photoluminescence of YM...     

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.     

Preparation and luminescence properties of Eu3+ doped oxyfluoride borosilicate glass ceramics

Oxyfluoride borosilicate glass with the molar composition of 60SiO2-15B2O3-15Na2O-8CaF2-2NaF-0.25Eu2O3 was synthesized by a traditional glass melting method. Glass ceramics containing CaF2 nanocrystals were prepared by heat treating the glass samples at a tem-perature in the range of 620-680 °C. The results of X-ray diffraction (XRD) indicated that the average crystallite size and the lattice constant of CaF2 nanocrystals increased with the heat treatment temperature increasing. The luminescence spectra showed that the emission intensity of Eu3+ doped glass ceramics was stronger than that of the glass matrix, and increased with the heat treatment temperature increasing. The left edge of excitation band shifted to shorter wavelength in the glass ceramics. The local environments of Eu3+ ions in the glass and glass ceram-ics were different.     

Impact of Yb3+/Er3+ions on crystallization of phosphosilicate glass melts

Transparent glass ceramics were prepared from the phosphosilicate system by melt-quenching devitrification(MQD) method, i.e., nanocrystals spontaneously form during cooling of the melts. Introduction of 2.5 wt.% Yb2O3 and 0.5 wt.% Er2O3 into the glass melt induced the change of type and concentration of crystals. The comparison of rheological and thermodynamic properties of both undoped and Yb3+/Er3+ doped melts showed that addition of Yb3+/Er3+ oxides caused increase of liquid fragility, and degree of medium-range order. In addition, the thermodynamic barriers for nucleation ΔG* as a function of reduced temperature T/Tm were calculated with an assumption of wetting angle θ=90o, Yb3+/Er3+ doped melt tended to firstly nucleate as compared to undoped melt at small undercooling.     

Role of localized phonon vibration in luminescence performance of Pr doped Ba(Mg0.28Zr0.16Ta0.56)O3 transparent ceramics

Oxygen-assisted high temperature solid-state reaction approach was employed for the fabrication of Pr activated Ba(Mg_0.28Zr_0.16Ta_0.56)O₃ transparent ceramic phosphor. Retiveld refinement of X-ray diffraction pattern was carried out to reveal the lattice parameters and crystal structural information. Under the blue-light excitation of λ_ex = 473 nm, the phosphor exhibits a sharp intense red emission centered at 645 nm, accompanied by several other weak peaks. PL evolution with temperature shows a significant luminescence quenching behavior, and the underlying multi-phonon interaction with optical center is revealed by proposing an unprecedent theoretical calculation work. Such a phonon effect is further confirmed from the red-shift of peak position with temperature, and the involved phonon energy of 50.7 meV is determined from Raman scattering measurement. More interestingly, the fitted results of transient-state PL spectra show a fluctuation of luminescence lifetime at various temperatures, further indicating a significant effect of phonon vibration in the system.     

Preparation and luminescence properties of Ce3＋/Dy3＋-codoped fluorosilicate glass ceramics

The Ce3+and Dy3+ co-doped fluorosilicate glass and glass ceramics containing SrF2 or CeF3 nanocrystals were prepared under re-ducing atmosphere. The precipitated nano-crystalline phase shifted from cubic SrF2 to hexagonal CeF3 gradually with the heat treatment tem-perature increasing from 620 to 680 °C. The glass and glass ceramics emitted white light, deriving from a combination of the Ce3+ blue and the Dy3+ yellow light. The CIE coordinates could be tuned by adjusting the ratio of Ce3+/Dy3+ concentration. The luminescence could be en-hanced significantly by annealing the samples at the temperatures lower than 640 °C.     

Microwave assisted synthesis,sinterability and properties of Ca-Zn co-doped LaCrO_3 as interconnect material for IT-SOFCs

The interconnect materials La0.7Ca0.3Cr1-xZnxO3-δ(x=0,0.01,0.03,0.05,0.07) were prepared by a microwave assisted sol-gel auto-ignition process.The crystalline structures of the samples were characterized by X-ray diffraction(XRD) and the lattice parameters were evaluated with Rietveld method.For Ca-Zn co-doped LaCrO3 with x=0.03,the sintering activity was improved,and the relative density came up to 96.5% for the sample sintered at 1300 oC for 10 h.The electrical conductivity of the samples was increased from 21.1 S/cm to the maximum of 70.9 S/cm at 650 oC in air,with the x content increasing from 0.01 to 0.03.However,with x further increasing,the electrical conductivity was decreased.The average thermal expansion coefficient(TEC) of the samples at RT-1000 oC in air was ca.10.0×10-6 K-1.All data indicated that the La0.7Ca0.3Cr1-xZnxO3-δ series ceramics would be potential candidate to be used as an interconnect materials for IT-SOFCs.