Papers by Author: Xu Dong Sun

Abstract: LYSO:Ce single crystal was widely manufactured by Czochralski method. Considering its high cost and the pollution of the crucible, we tried to prepare the crystal by Verneuil method. Unlike Czochralski method, the Verneuil method need the powders with excellent fluidity and high purity. By comparing the powders annealed at 1100°C,1200°C,1300°C,1400°C and 1500°C, we can obtained the needed powders at 1500°C. We also increased the content of silica to satisfy the volatilization in crystal growth process. The single crystal was prepared by changing the growth parameter. We investigated the phase and the microstructure of the powders and observed the microstucture of the crystal fracture. We discussed the improved method of the process of crystal growth.

Abstract: Sulfate-ion pillared layered hydroxide of Eu₂(OH)₄SO₄·nH₂O (n~2, SO₄^2--LEuH) was synthesized through controlled hydrothermal reaction, and the phase evolution of which upon calcination in the air and hydrogen was studied in detail. It was found that annealing in the air produced orthorhombic Eu₂O₂SO₄ in the temperature range of 300-1000 °C while in flowing H₂ hexagonal Eu₂O₂S was resulted in the 600-1000 °C range. Strong red emissions were found at 621 nm for the SO₄^2--LEuH and 627 nm for Eu₂O₂S under excitation at 396 nm (the ⁷F₀-⁵L₆ transition of Eu³⁺). Improved luminescence intensity was also observed for the Eu₂O₂S powder calcined at a higher temperature.

Abstract: Two dimensional nanophosphors of high quality play an important role in the miniaturization and intelligentization of opto-electronic components. In this present work, ultra-large (30μm) single crystals of (Y_0.95Eu_0.05)₂(OH)₅NO₃·nH₂O layered rare earth hydroxide (LRH) with a hexagonal shape have been synthisized via autoclaving the rare-earth nitrate/NH₄OH reaction system in the presence of ammonium nitrate (NH₄NO₃). The nitrate ions, existing in the interlayer gallery of layered rare earth hydroxide, exhibit facile exchanges with oleate anions by hydrothermal anion exchange. Furthermore, the interlayer distance can thus be expanded from ~0.9 nm for the pristine LRHs to ~3.60 nm for the intercalated ones, which are then efficiently delaminated into unilamellar nanosheets with a lateral size of 10μm and a thickness of ~1.50 nm. The obtained nanosheets are single crystaline. Highly [11 oriented, dense (Y_0.95Eu_0.05)₂O₃ phosphor films with excellent optical transparency and a greatly enhanced luminescence intensity have been constructed via self-assembly of ultra-large unilamellar LRH nanosheets, followed by proper annealing.

Abstract: Uniform spherical alumina powders have been synthesized via homogeneous precipitation method from aluminum nitrate using urea as the precipitant. The amount of ammonium sulfate has a significant effect on morphology and particle size of the precursor powders. It was found that spherical particles can be obtained when the molar ratio of ammonium sulfate to aluminum nitrate is about 0.72 and the concentration of the aluminum nitrate is 0.005M. Spherical alumina particles with 400 nm in diameter were obtained by calcining the precursors at 1100°C for 4 hrs.

Abstract: Ca₃Co₄O₉ powders were synthesized by a solid-state reaction method. Porous Ca₃Co₄O₉ ceramics with parallel sheet shaped pores were prepared by a template sacrifice method using epispastic polystyrend (EPS) hollow spheres as the templates. During compaction of the green body, the EPS hollow spheres change into EPS discs due to the pressing force. After sintering, the pores in the Ca₃Co₄O₉ ceramics are sheet shaped, well distributed and parallel to the pressing surface of compaction. The value of ZT merit of the porous Ca₃Co₄O₉ sample obtained with 10 wt% EPS spheres is 0.0489. It was found that the ZT merit value can be improved by changing the density of sample to achieve a high ratio of electrical conductivity to thermal conductivity.

Abstract: Magnesium has been recently recognized as a biodegradable metal for bone substitute applications. In the present work, a novel magnesium based scaffold with a specific two-layer structure was prepared for powder metallurgical process. The outer layer of the scaffold shows an interconnected porous structure, so that the fresh fluid can be easily sent into the material, allowing the ingrowth of new bone tissue. The inner compact structure reinforced by the salt particles can increase the strength of the material. Structural characterizations and mechanical tests of the materials demonstrate that the structural and mechanical properties of the magnesium-based scaffold with an appropriate salt content prepared by the current method are quite comparable to those of cancellous bone. Therefore, the magnesium-based scaffold with such a two-layer structure has the potential to serve as degradable implants for bone substitute applications.

Abstract: A series of layered rare-earth hydroxides (LRHs) of (Y,Ln)₂(OH)₅NO₃•nH₂O ( Ln=Tb,Eu), have been synthesized via a hydrothermal route. Crystal structures and optical properties of the materials have been investigated in detail by the combined techniques of XRD, FT-IR, FE-SEM, HR-TEM, and PLE/PL spectroscopies. It is shown that Tb³⁺ and Eu³⁺ are successfully incorporated into the Y-LRH host lattice to form solid solutions. Under UV excitation, the binary (Y_0.97Tb_0.03)- and (Y_0.97Eu_0.03)-LRHs exhibit their respective characteristic photoluminescence of the Eu³⁺ and Tb³⁺ activators. The ternary (Y_0.965Eu_0.005Tb_0.03)-LRH simultaneously shows red and green emissions and both the intensity and emission color can be adjusted by changing the excitation wavelength. Compared with (Y_0.995Eu_0.005)-LRH, the ternary (Y_0.965Eu_0.005Tb_0.03)-LRH exhibits appreciably enhanced 615nm red-emission, which indicates the existence of non- radiative energy transfer from Tb³⁺ to Eu³⁺. The ternary (Y_0.965Eu_0.005Tb_0.03)-LRH also readily undergoes anion exchange with a series of inorganic and organic anions at room temperature.

Abstract: Fine yttrium stearate powder was produced at a relatively low temperature using yttrium nitrate hexahydrate, ammonia and stearic acid as the raw materials. Dispersed Y₂O₃ nanopowder was synthesized by calcining the yttrium stearate. The formation mechanism of the precursor and the Y₂O₃ nanopowder was studied by means of XRD, TG-DTA, FT-IR, BET, FE-SEM and HR-TEM. Pure and dispersed Y₂O₃ nanopowder with an average particle size of 30 nm was produced by calcining the precursor at 600 °C. The particle size increases to about 60 nm with the increase of the calcination temperature to 1000 °C. In the preparation of Y₂O₃ from yttrium stearate, no water medium is involved, thus capillarity force and bridging of adjacent particles by hydrogen bonds can be avoided, resulting in good dispersion of the particles. The dispersed Y₂O₃ nanopowder prepared in this work has potential application in phosphors and transparent ceramic materials.

Abstract: To suppress the thermal decomposition and to stabilize the crystal structure of Gd₃Al₅O₁₂ (GdAG) garnet, doping GdAG with smaller Ln³⁺ (Ln=Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y, respectively) to form (Gd,Ln)AG solid solutions was proposed in work. Carbonate precursors of (Gd,Ln)AG with an approximate composition of (NH₄)_x(Gd,Ln)₃Al₅(OH)_y(CO₃)_z•nH₂O were synthesized via coprecipitation from a mixed solution of ammonium aluminum sulfate and rare earth nitrate, using ammonium hydrogen carbonate as the precipitant. The precursors and the calcination derived oxides were characterized using FT-IR spectroscopy, DTA/TG, XRD, BET and FE-SEM. The results showed that smaller Ln³⁺ doping can indeed stabilize GdAG against its thermal decomposition to a mixture of GdAlO₃ (GdAP) and Al₂O₃ phases at elevated temperatures and at the same time effectively lowers the temperature for garnet crystallization. The carbonate precursors are loosely agglomerated and the resultant (Gd,Ln)AG powders show good dispersion and a fairly uniform particle morphology. The (Gd,Ln)AG solid solutions exhibit decreasing lattice parameters along with decreasing radius of the dopant ions at the same dopant content of 50 at%. Photoluminescence properties of some of the garnet solid solutions are also studied. The materials developed herein may potentially be used for photoluminescent and scintillation applications.

Abstract: Ce0.5Ti0.5O2 ion storage films were prepared by using sol–gel routes employed butyltitanate（Ti(OC4H9)4） and cerium nitrate（Ce(NO3)3•6H2O） as main initial materials. Structural, optical and electrochemical properties were investigated by XRD, SEM, cyclic voltammetry curves and utraviolet visible spectroscopy in this work. Ce0.5Ti0.5O2 ion films contained crystallization CeO2 and amorphous TiO2, and had large ion storage capacity. Its injection of charge density was high to 12.01 mC•cm-2 and K value was 0.75. It had better cyclic reversibility and high transparency, which kept colorless and transparent during the whole injection and extraction process of Li+. Light insert ion storage films of Ce0.5Ti0.5O2 has important significance in the preparation of electrochromic device.