Materials Science Forum Vols. 663-665

Abstract: A simple solution chemical route for bulk synthesis of hand-like Bi2O3 microcrystals has been demonstrated. The microcrystals are assembled by several short rods that have a diameter in the range of 50-500 nm, and a length in the range of 1-20 μm. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) were employed to characterize the structure and morphology of these novel structures. The field emission of the sample started at a turn-on field of 2.1 V/μm at a current density of 0.1 μA/cm2, while the emission current density reached about 0.1mA/cm2 at an applied field of 5.5 V/μm. These results suggest that hand-like Bi2O3 microcrystals can be an excellent FE material candidate.

Abstract: PL spectra of Ca2-xBO3Cl:xDy3+ phosphors excited by 390 nm n-UV light. The intensity of both blue and yellow emissions starts to increases with the growing contents of Dy3+ ions, the strongest intensity of Dy3+ emission courses in the Ca1.95BO3Cl:0.05Dy3+ phosphor, subsequently it decreases with further adding Dy3+ ions due to concentration quenching. it can be concluded that the environment of Dy3+ ions may be less influenced due to the clustering of Dy3+ ions in the investigated phosphors after concentration quenching.

Abstract: In the laser forming of metal plates, there is a substantial waiting time required for cooling down the workpiece so that a steep temperature gradient can be reestablished during the next scan. Currently, there are no standard techniques that can be used to reduce this waiting time. This paper discusses the possibility of using non-natural cooling systems to cool down the workpiece. A numerical model of thermo-mechanical analyses with moving boundary conditions to simulate the traveling of laser beam and moving forced water cooling system is presented. Based on the proposed model, cooling effects under different laser powers and scanning velocities with various cooling conditions are investigated. The results show that the forced water cooling can significantly reduce the temperature with no adverse effect on the forming of plates.

Abstract: We report the structural and photoluminescence properties of CdTe/Porous silicon (PS) composite system prepared by chemical vapor deposition. The XRD pattern accord with the standard pattern of cadmium telluride of the samples was evaluated and the morphology of CdTe particles was characterized by scanning electron microscopy. The composite sample gives a strong luminescence and the mechanism of photoluminescence with CdTe/PS has also been discussed.

Abstract: A series of long persistent phosphors Sr1-3x Al2O4 : Eu2+xDy3+2x (X=0.005, 0.010, 0.015, 0.020, 0.025)were prepared through a combustion method at 600oC. We found that all the series of samples have good long afterglow properties by the naked eye. Then we use the laser to stimulate phosphors at 325nm, and their emission spectrums were tested by a spectrograph. We can found that the emission peaks of all samples are all results from the 4f65d  4f7 (8S7/2) transition of Eu2+ instead of the 4f7 (6P7/2)  4f7 (8S7/2) transition of Eu2+ ions. In addition, the afterglow characteristic of the various samples and the same sample at different wavelengths was investigated. Our results show that each decay curve consists of a rapid decay part followed by a long slow one and all samples have the same afterglow mechanism.

Abstract: Rare-earth metal-organic frameworks [Tb2(pdc)3(H2O)9]n3nH2O, were synthesized and characterized by elemental analysis, IR spectra and single-crystal X-ray diffraction. The title compound consisted of one-dimensional dual-chains, in which each metal atom is nine-coordinated with oxygen atoms. The carboxylate groups of pdc provided two kinds of coordination ways as bidentate and monodentate. The solid-state photoluminescence measurement exhibited green light-emitting characteristic of terbium (III) coordination polymer, and the fluorescence intensities were stronger than that of the europium compound with the same ligand.

Abstract: New electron doped double perovskite compound (Sr2-xSmx) FeMoO6 (0≤x≤0.25) has been synthesized by solid-state reaction. Crystal structure and magnetic properties of the compounds have been investigated by X-ray powder diffraction (XRD) and magnetic measurements. XRD revealed that all the compounds were of single phase and belonged to a I 4/m lattice. The degree of cationic ordering on the B site was decreased pronouncedly by the electron doping. Different from the results of La- and Nd-doped Sr2FeMoO6, Curie temperature (TC) of (Sr2-xSmx) FeMoO6 decreased first with the doping and then increased beyond x = 0.15, indicating that steric effect was enhanced as the radius of rare-earth ions decreased.

Abstract: Sapphire (α-Al2O3) single crystal, as an important photoconducting device substrate material, stringent surface quality requirements, i.e. surface finish and flatness, are required. The use of chemical mechanical polishing (CMP) technique can produce high quality surface finishes at low cost and with fast material removal rates. The polishing mechanism was studied in this paper, and it was pointed that there were chemical and mechanical kinetics process respectively. The chosen polishing temperature was 40 oC. SiO2 sol was chosen as abrasive and the particle size is 40nm. The pH value was determined at 11.5~12. During CMP process C6382I-W/YJ single side polisher and SUBA 600 pad were used. After polishing and cleaning of sapphire surface, the measured removal rate was above 183.3nm /min and the surface roughness by using AFM was lower than Ra 0.3 nm. From the results, it was found that using such method, the optimal sapphire surface can be gotten, which is advantaged for epitaxial growth and device making-up.

Abstract: A series of long persistent phosphors Sr0.985-x Al2O4 : Eu2+0.015Dy3+x (X=0.000, 0.010, 0.020, 0.030, 0.040) were prepared through a combustion method at 600oC. We found that all the series of samples have good long afterglow properties by the naked eye. Then we use the laser to stimulate phosphors at 325nm, and their emission spectrums were tested by a spectrograph. We can found that the main emission peaks of all samples are all results from the 4f65d  4f7 (8S7/2) transition of Eu2+ instead of the 4f7 (6P7/2)  4f7 (8S7/2) transition of Eu2+ ions located about 515nm. In addition, the afterglow characteristic of all samples was investigated. Our results show that each decay curve consists of a rapid decay part followed by a long slow one and all samples have the same afterglow mechanism. And the Dy ions play an important role on the afterglow process.

Abstract: ZnO nanorod arrays were prepared using a chemical solution route on fluorine-doped SnO2 conductive glass pre-coated by a thin ZnO seed layer. Morphology, crystal structure and growth direction of the nanorod arrays were characterized by SEM and XRD respectively. The SEM results demonstrated that ordered arrays of ZnO nanorods grew vertically on the substrate. XRD measurement revealed the ZnO nanorods were grown along the [002] direction of the ZnO crystallites. Under optimal condition, ZnO nanorods with the average length about 6-7 μm and the diameters about 10nm at the tip and 150 nm at the base were obtained. The optical properties of ZnO nanorod arrays were characterized by transmittance spectra and photoluminescence measurement at room temperature.