Fan Xianping

Luminescence of Bi3+ ions and energy transfer from Bi3+ ions to Eu3+ ions in silica glasses prepared by the sol-gel process

Abstract Luminescence of Bi3+ ions and energy transfer from Bi3+ ions to Eu3+ ions in silica glasses prepared by the sol-gel process have been investigated. The results showed that the excitation band of Bi3+ ions corresponds to the 1 S 0 → 1 P 1 transition and emission spectra consists of a single broad band without structure centred at 395 nm, which corresponds to 3 P 1 → 1 S 0 transition. When a small amount of Bi3+ ions was introduced to 1 mol% Eu3+ ions the doped silica gel glass emission intensity of Eu3+ ions got significantly stronger, which suggests very efficient energy transfer from Bi3+ ions to Eu3+ ions. It can be assigned to significant energy overlap between the emission band of the Bi3+ ion and the excitation band of the Eu3+ ion. However, due to a larger energy overlap between emission and excitation bands of Bi3+, when Bi3+ ion concentration in silica gel glasses was more than 0.5 mol% the probability of energy transfer between Bi3+ ions increased rapidly and the probability of energy transfer from Bi3+ ions to Eu3+ ions decreased relatively. As a consequence, the sensitized effectiveness of the Bi3+ ion on the emission spectrum of the Eu3+ ion drastically decreased with increasing Bi3+ ion concentration.

Synthesis in situ of 2,2′-dipyridyl-Tb(iii) complexes in silica gel

Abstracts are not published in this journal

Structural evolution and fluorescence properties of Tb3+-doped silica xerogels in the gel to glass conversion

The Tb3+-doped silica glasses were prepared by a sol-gel process with appropriate heat treatment. The structural changes during the gel to glass transition of Tb3+-doped silica xerogels and the effect on fluorescence properties of Tb3+ were studied in this paper. The results show that the doped silica glasses may be obtained after the xerogels are heat-treated at 800 °C for 24 h. During heat treatment at 400 °C, the residual organic molecules and most of the absorbed water molecules in silica xerogels are removed, and the SiO4 tetrahedral structural network forms and strengthens gradually with decreasing number of silanol (SiOH) groups. The fluorescence intensity of Tb3+ ions increases remarkably when the doped xerogel is heat-treated in the range 300–500 °C, and increases slowly above 500 °C(up to 800 °C). This observation leads to a conclusion that the radiative transitions of Tb3+ ion in the aqueous gels are quenched strongly by the high-frequency vibrations of OH groups from the coordinated water rather than physically absorbed water. The inhomogeneity in the site state of Tb3+ ions increases with rise in temperature of heat treatment, which broadens the emission bands of Tb3+ ions doped in silica glasses. Moreover, there will also be an additional interaction owing to the influence of the ligand field of the glasses, which makes the emission bands shift to red and produces Stark splitting of the Tb3+ ion energy levels.

Synthesis of Yttrium Oxide Nanocrystal via Solvothermal Process

Abstract Y 2 O 3 nanomaterials have been widely used in transparent ceramics and luminescent devices. Recently there are many studies focusing on controlling the size and morphology of Y 2 O 3 in order to obtain better materials performance. In present study, yttrium oxyhydroxide precursor was synthesized via a facile solvothermal process through the dissolution-recrystallization mechanism of Y 2 O 3 raw powders in the ethylenediamine solvent, then nanosized yttrium oxide crystal was prepared from the precursor through post heat treatment process. The effects of solvothermal treatment temperature, holding time, solvent kinds and post heat treatment parameters on crystalline structure, grain shape and size of nanocrystal were investigated by XRD, TEM and TGA-DTA measurements. TEM images reveal that the morphology of product after post heat treatment at 460 °C for 12 h is rice-like nanocrystal. XRD shows that this product is pure cubic Y 2 O 3 cphase. Present study reveals that high purity Y 2 O 3 with rice-like morphology can be easily prepared with average size around 30 nm under suitable post heat treatment parameters. In addition the effects of solvents such as water and ethanol etc. on the crystal structure and morphology were also investigated. It is suggested that dissolution-recrystallization process may be the main mechanism for the formation of nano-sized YOOH precursors under solvothermal reaction condition, and the ethylenediamine solvent is likely to play an important role in controlling the transformation process of yttria precursors to the Y 2 O 3 nanocrystal.

Study of phase separation in Na2OB2O3SiO2 glasses by tem and optical diffraction

Abstract As an extension of the small angle X-ray scattering and electron microscopy techniques for investigating phase separation in glasses, a method has been developed which involves taking electron microscopy phase separation morphology micrographs and then using an optical diffractometer (OD) to perform a Fourier transformation so as to obtain the small angle scattering intensity. By using this method, phase separation in Na 2 OB 2 O 3 SiO 2 glasses was investigated. The results obtained are as follows: (1) The size of the interconnecting phase-separated particles measured by this method seemed to be proportional to the cube root of the heat treatment time. (2) The sequence of phase separation in the three liquid regions of the Na 2 OB 2 O 3 SiO 2 system is as follows: first, the glasses separate into a silica-rich phase and a sodium-borate-rich phase , and then the sodium-borate-rich phase separates into two other phases, on being borate-rich and the other sodium-rich.

The influence of the matrix on the fluorescence properties of pyrene

The fluorescence properties of pyrene doped in silica xerogels by a sol-gel process and dissolved in ethanol in various concentrations were studied comparatively. With increasing gelation time the fluorescence spectra of pyrene doped in silica gels change greatly. Pyrene monomer excitation bands arise gradually with decreasing intensity of pyrene excimer excitation bands, which increases the intensity of the monomer emission and decreases that of the excimer emission. Compared with dissolving pyrene in ethanol, doping with pyrene in silica xerogels can increase the quenching concentration of pyrene enormously and thus increase the monomer fluorescence intensity of pyrene by a factor of approximately 20 with respect to that in ethanol solution. These changes can be explained by the modification of the pyrene surroundings. The pyrene molecules are isolated and absorbed in the tiny pores of the silica network steadily to avoid aggregate formation in silica xerogels.

A Novel Method for the Preparation of Ag/SnO2 Electrical Contact Materials

Abstract A novel method was presented to prepare Ag/SnO2 (12 wt% SnO2) electrical contact materials. First, Ag-SnO2 nano composite powder with 42 wt% SnO2 synthesized by a coprecipitation method was characterized. XRD results reveal that the synthesized composite powder is composed of cubic Ag and rutile type of SnO2. SEM and TEM images show that nano-Ag and nano-SnO2 particles are homogeneously dispersed in the composite powder. The preparation process of nano composite powder was analyzed with the help of the TG-DTA curves of the precipitation. Then, the obtained Ag-SnO2 nano composite powder was mixed with Ag powder to prepare Ag/SnO2 electrical contact materials (ECM) by powder metallurgy process and the prepared Ag/SnO2 electrical contact materials was characterized. The results demonstrate that owing to the higher dispersion of nano SnO2 particles in Ag matrix, the physical properties of ECM prepared by the new method, such as the density, hardness and conductivity are better than that by the traditional method.

Luminescence Characterization of Mg Doped Y2O2S:Ti Long Afterglow Phosphor

Abstract Y 1.94- x Mg x O 2 S:0.06Ti (0≤ x ≤0.10) phosphors with long afterglow were synthesized by solid state reaction route. The photoluminescence spectra, decay curves, thermoluminescent spectra and chromaticity coordinate curves were investigated. The results show that the luminescence intensity of Y 1.94- x Mg x O 2 S:0.06Ti (0≤ x ≤0.10) phosphors decrease gradually with increasing Mg 2+ ion content, and the shape of luminescence spectra and chromaticity coordinate change as well. Furthermore, two thermoluminescent peaks in single Ti-doped Y 2 O 2 S sample are found at 91.8 and 221.5 °C, respectively. Nevertheless, significant different spectra were found for the Mg, Ti co-doped Y 2 O 2 S samples that three thermoluminescence peaks appear at 52.3, 141.7 and 226.8 °C, respectively. These results indicate that the co-doped Mg ion changes the inherent trap depth of single Ti-doped Y 2 O 2 S: Ti phosphor, and induces simultaneously a new trap level in the Y 1.94- x Mg x O 2 S:0.06Ti phosphor. Based on the analysis of thermoluminescent spectra, photoluminescent spectra, decay curve and crystal structure defect, it was proposed that the varied structure defect and introduced new trap level by the doped Mg 2+ ions should be responsible for reducing luminescence intensity and varying color in the Y 1.94- x Mg x O 2 S:0.06Ti phosphor.

The Preparation and Photoluminescence Properties of Fluorosilicate Glass Ceramics Containing CeF3:Dy3+ Nanocrystals

Ce3+ and Dy3+ co-doped oxyfluoride glasses and glass ceramics containing CeF3 nanocrystals are prepared in a reducing atmosphere. XRD measurements and the calculated lattice parameters suggest that Dy3+ ions are incorporated with precipitated CeF3 nanocrystals along with a rise in the Dy3+ concentration or an increase in the annealing temperature. The glass ceramics emit white light close to the CIE coordinates of (0.3,0.3), derived from a combination of Ce3+ and Dy3+ emission. The CIE chromaticity coordinates of the Ce3+ and Dy3+ co-doped glass ceramics can be tuned by varying the ratio of Ce3+/Dy3+, while the luminescence intensity can be enhanced by heat treatment above 620°C.

Anti-Arc Erosion Properties of Ag-La2Sn2O7/SnO2 Contacts

Abstract La2Sn2O7/SnO2 composite powder was synthesized by chemical co-precipitation, and Ag-La2Sn2O7/SnO2 electrical contact material was prepared by a powder metallurgy method. Anti-arc erosion properties, mass loss and Vickers hardness of the Ag-La2Sn2O7/SnO2 composite were investigated, and its anti-arc erosion mechanism was discussed. Results show that the welding force of Ag-La2Sn2O7/SnO2 composite is much better than that of Ag-SnO2, because the new phase La2Sn2O7 can increase the viscosity of melt pool and improve wettability between silver and tin oxide to some extent. Meanwhile, Flatter arcing area and “beads-like” particles embedded scatteredly in the surface could decentralize arc energy via “pinning effect”, which decreases temperature rise and weakens the damage of surface structure, and better anti-welding property is obtained. Ag-La2Sn2O7/SnO2 composite could be a leading candidate material for electrical contacts in the future.