Papers by Author: Shi Kao Shi

Abstract: (PO4)3- -doped red phosphors, Na5Eu(MoO4)4-x(PO4)x (x ≤ 0.10), were prepared by the conventional solid-state reaction method, and their luminescent properties were studied. Under the excitation of near-UV 395 nm, the phosphors show intense red emission. In particular, the relative emission intensity of Na5Eu(MoO4)3.96(PO4)0.04 sample reaches about 5.0 times in comparison with that of the commercial red phosphor Y2O2S:Eu3+. The phosphor could be suitable for the application of white light-emitting diodes.

Abstract: The lithium ions doped red-emitting phosphors of (Ca,Eu)WO4 and (Ca,Eu)MoO4 were synthesized by solid-state reaction method, and their luminescent properties were investigated. The XRD patterns show that the phosphors are isostructural and share a tetragonal scheelite structure, even some lithium ions are doped. The excitation spectra consist of broad charge transfer bands in the short-wave UV region of W6+→O2- and Eu3+→O2- with three sharp lines around 395, 465 and 535 nm of the Eu3+ 4f excitation transitions. The characteristic emissions of WO4 2- and MoO4 2- are quenched absolutely and red light emission of Eu3+ exhibits predominate peak around 615 nm due to the electric dipole energy transition of 5D0→7F2. Excited with 395 nm, the evident enhanced emission of the phosphors were observed when Li+ doped in the host, which implies that the addition of some Li+ is beneficial for the energy transfer from WO4 2- or MoO4 2- to Eu3+.

Abstract: Surfactant-zirconium phosphate composites were prepared by surfactant cetyltrimethylammonium bromide intercalating to α-zirconium phosphate. The interlayer spacing of the lamellar structure was greatly expanded to 39.6 Å, as compared to 7.6 Å of α-zirconium phosphate. The molar ratio of surfactant to α-zirconium phosphate in the composites was found to be 1/1.46. The expanded interlayer separation is beneficial for complicated guest molecules intercalating to the galleries of the composites.

Abstract: Sulfide nanowire arrays have been synthesized by DC electrodeposition from an electrolyte containing S in DMSO. The AAO membrane with the barrier layer has been directly used as template in electrodeposition. The as-synthesized products are characterized by SEM, TEM and resonance Raman spectroscopy. CdS and ZnS nanowires have been obtained, respectively.

Abstract: A series of powders of (Ba1-xLa2x/3)(Ti1-xNb4x/5)O3 (0.05≤x≤0.3) have been synthesized by solid-state reaction route, and the effects of the dopants on the microstructure of BaTiO3 were investigated by XRD, SEM, HTEM and EDS in the BaTiO3-La2O3-Nb2O5 ternary system. It was found that the secondary titanium-rich phase occurred for x ≤ 0.1, while Ba3La3Ti5Nb5O30 yields as secondary phase for x ≥ 0.2. In the whole range of 0.05 ≤ x ≤ 0.3, the crystal structure of BaTiO3 solid solutions is cubic system. There are two substitution modes in the system: the substitution mode of La ions dissolved into Ba sites is significant for x ≤ 0.2, but the substitution mode of Nb ions dissolved into Ti sites is significant for x>0.2. TEM observation and EDS analysis revealed that the concentration gradient of Nb existed and La almost distributed homogeneously in a grain. Thus, the dielectric materials composed of La-Nb-codoped BT are not fitted to form the core-shell structure for the higher dopants.

Abstract: Infrared-to-visible upconversion phosphors Y2O3: Yb, Er and Gd2O3:Yb, Er with narrow size distribution were synthesized by using a stable microemulsion system, which included triton X-100, n-hexanol, cyclohexane and water. Appearance-controllable nanocrystals were achieved by adjusting the ratios of assistant surfactant and surfactant. The X-ray diffraction patterns of the samples showed that the powders were cubic phases of Y2O3 and Gd2O3, respectively. After calcination with different temperature settings in air atmosphere, the particles were spherical through the observation by scanning electronic microscopy. Red and green upconversion luminescence was obtained under 980 nm infrared excitation. Several contributions to the intensity of upconversion emission were also investigated. These upconversion phosphors may be used as fluorescent labels for the sensitive detection of biomolecule, immunoassay or DNA assays.

Abstract: The precursor powder of Sr2CeO4 was prepared from a nitrate starting solution by a combustion route with urea as a fuel. Sintering the precursor powder at different temperatures for 6h, a blue-white emission phosphor was synthesized. The microstructure and photoluminescence studies of Sr2CeO4 compound are reported. The particle sizes of the powder phosphor are around 0.5-2 µm when heat treated between 9500C to 11500C and the emission spectrum exhibits a broad band maximum at about 470 nm. The chemical purity and photoluminescence intensity of Sr2CeO4 powder phosphor strongly depend on the post-heat-treated temperature.

Abstract: We have improved an electrochemical process in which the alternate current (AC) electrodeposition combined with the etching of substrate to prepare transparent metallic nanoparticles and anodic alumina oxide (AAO) composite films. The new process greatly simplifies the direct current (DC) electrodeposition process to get transparent composite films. Moreover, the electrocrystallization mechanism has been analyzed. The Ag, Cu and Ag-Cu co-deposited nanoparticles/AAO films have distinct absorption peaks, which can be ascribed to the surface plasmon resonance (SPR) of these noble metal nanoparticles.

Abstract: Carbonate precursor of Eu3+ doped Sr2CeO4 is obtained from a mixed solution of strontium, cerium and europium nitrate using ammonium carbonate as precipitant. Calcining the carbonate precursor at different temperatures, the Eu3+ doped Sr2CeO4 phosphor is synthesized. The phase purity of the material is closely related with the calcination temperature, and the phosphor with high purity can be achieved after the precursor annealed at 1200°C. The photoluminescence performance for Eu3+ doped Sr2CeO4 depends on the concentration of Eu3+. The excitation and emission reveal efficient energy transfer from Ce4+ to Eu3+, making the emission light from blue-white to red-white, further to red as the Eu3+ concentration gradually changes from low concentration (1 mol%) to high concentration (10 mol%).