Browsing by Author "Shi, Shikao"
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- Combustion synthesis of Ce 2 LuO 5.5:Eu phosphor nanopowders: structure, surface and luminescence investigationsPublication . Shi, Shikao; Wei, Dan; Li, Keyan; Wang, Shuping; Fu, Lianshe; Yang, Tao; Meng, LijianThe spherical shape, uniform size and small degree of agglomeration of the particles play crucial roles in promoting the practical applications of the phosphor powders. In this paper, the novel Eu3+ -doped cerium lutetium Ce2LuO5.5 composite nanopowders with a cubic fluorite structure were prepared via a typical solution combustion route, and their internal structure, surface morphology as well as luminescence properties were investigated. The Eu3+ could substitute in either Lu3+ or Ce4+ sites and the existence of oxygen vacancy was confirmed in the composite by X-ray diffraction and Raman spectra techniques. Without the addition of surfactant, most of the as-prepared particles were bound together, and the luminescence was very weak even after a sintering process. Assisted with appropriate polyvinyl alcohol (PVA) surfactant in the combustion reaction and a subsequent heat-treatment process, the bound-particles were evidently separated and seemed to be nearly spherical shape. The particle size could be controlled to 30-120 nm and the luminescence was enhanced by adjusting the subsequent sintering temperature. Excited with 466 nm blue light, the nanopowders exhibited characteristic 5D0→7FJ (J = 0∼ 4) emission transition of Eu3+ and showed enhanced red luminescence as Eu3+ occupied Ce4+ site rather than Lu3+ site. The maximum emission was obtained as 40 mol% Eu substitutes Ce in the composite. Due to the coincidence of 466 nm excitation light with the emission of InGaN chips in white light-emitting diodes, the surface-morphology improved Eu-doped Ce2LuO5.5 phosphor nanopowders have a potential application in solid state lighting fields.
- Highly branched Pt Cu nanodandelion with high activity for oxygen reduction reactionPublication . Yang, Tao; Pukazhselvan, D.; da Silva, E.L.; Santos, Mario C.; Meng, Lijian; Ramasamy, Devaraj; Jothi, Sathiskumar; Graça, Vanessa; Shi, ShikaoA facile hydrothermal route has been developed to synthesize the highly branched Pt58Cu42 nanoparticles via mixing the H2PtCl6 and CuCl2 with octadecylamine. The Pt58Cu42 after post treatment forms a dandelion flower 3-D structure. A combination of both the branched shape and PtCu composition effects in the Pt58Cu42-nanoparticles shows superior electrocatalytic activity and durability to commercial Pt black for oxygen reduction reaction. The mechanism for the de-alloying and reconstructing of the Pt58Cu42-nanoparticles in electrochemical activity and durability tests has been proposed. It is found that after the durability process, the Pt58Cu42 precursor alloy changes into a substantially Pt enriched PtCu alloy (Pt79Cu21) with a Pt skin. The Pt skin effectively prevents the further dissolution of the Cu below the near-surface to enhance its durability. What's more, the Pt skin exposed to (111) planes which have the lowest surface energy among the low-index planes further promotes the improvement of durability of the PtCu catalyst.
- Hydrothermal synthesis and optimization of boron doped LiZr2(PO4)3 Li-ion solid electrolytePublication . Yang, Tao; Almeida, Carlosde; Han, Dezhi; Meng, Lijian; Deng, Jiguang; Silva, E.L. da; Santos, M.C.; Shi, ShikaoBoron doped LiZr2(PO4)3 electrolyte was successfully synthesized via facile hydrothermal synthesis. Our results show that boron doping mainly happens on the Zr-site of Li1+xZr2-xBx(PO4)3 not the P-site of Li1+6xZr2(P1-xBxO4)3. Rietveld refinement of the unit-cell parameters was performed, and it was verified by consideration of Vegard’s law that it is possible to obtain phase purity up to x= 0.05 in Li1+xZr2-xBx(PO4)3. This corresponds with phases present in the XRD data, which shows the additional presence of the low temperature (monoclinic) phase for the powder sintered at 1200ºC for 12h of compositions with x ≥ 0.075. The compositions inside the solid solution undergo the phase transition from triclinic to rhombohedral when heating from 25 to 100ºC.
- Study of nanostructural bismuth oxide films prepared by radio frequency reactive magnetron sputteringPublication . Meng, Lijian; Xu, Wei; Zhang, Qingyu; Yang, Tao; Shi, ShikaoBismuth oxide films were deposited onto quartz substrates by radio frequency reactive magnetron sputtering using a bismuth metal target. The substrate temperature was varied from room temperature to 500 oC. The state of Bi ions in the deposited films was characterized by XPS and the results showed that Bi ions existed as Bi3+ ions. The film structure was characterized by XRD and Raman scattering. The film deposited at room temperature shown a δ-phase predominant amorphous structure. As the substrate temperature was higher than 300 ºC, polycrystalline structure was formed. The film optical properties were studied by measuring the transmittance. The optical band gap was estimated by the Tauc plot, showing a red shift with the increase of the substrate temperature which gives it a potential application as a photocatalytic material for visible light.