Tomokatsu Hayakawa

Sharp cubic and octahedral morphologies of poly(vinylpyrrolidone)-stabilised platinum nanoparticles by polyol method in ethylene glycol: their nucleation, growth and formation mechanisms

Pt nanoparticles (NPs) were synthesised by a modified polyol method with the addition of silver nitrate. The results showed that the specific shapes of Pt NPs were influenced by the relevant factors, which are the contents of silver nitrate, synthetic time and temperature. A small content of silver nitrate has played an important role in determining their final shapes of platinum NPs. We observed that Pt NPs in the forms of very sharp shapes such as Pt cubes, octahedrons, cuboctahedrons and tetrahedrons have been obtained. In addition, the shape growth mechanisms and formation of Pt NPs have been studied. They exist in both cubic and octahedral shapes. Importantly, Pt nanocrystals can grow into main cubic and octahedral shapes for a short time less than 15 min. Moreover, Pt nanocrystals can also grow into different shapes from cubic and octahedral into spherical ones for several hours. Especially, they exhibited interesting shapes of multiple-branched Pt nanostructures because of their overgrowth and aggregations. Clearly, large cubic and octahedral Pt NPs of 160 nm diameter were observed. The growth and formation of large cubic and octahedral Pt NPs were due to the aggregation of Pt clusters or initial Pt seeds, even small Pt nanocrystals.

Size-dependence of LaF3:Eu3+ nanocrystals on Eu3+ photo-luminescence intensity

Size-dependence of Eu3+-doped LaF3 nanocrystals on the 5D0-7FJ photoluminescence intensity was investigated, where LaF3:Eu3+ nanocrystals were prepared through a hydrothermal route with a cationic surfactant cetyltrimethylammonium bromide (CTAB) as size-controlled agent and by post-annealing at an appropriate temperature at N2 atmosphere. It was found that LaF3:Eu3+ obtained was in hexagonal structure with space group P3c1 and had good crystalinity. When LaF3:Eu3+ nanocrystals were synthesized with 0.006 mol/L CTAB the average particle size was maximized to be 25.4 nm and the luminescence intensity was 1.5 times higher than that prepared without CTAB or with more CTAB concentration. The mechanism of the particle growth was also discussed in this paper.

Doping Effect of Transition Metal Ions on Magnetic and Optical Properties of EuO-Al2O3-SiO2 Glass

We previously reported Faraday rotation of EuO-Al2O3-SiO2 glass operating in the visible region. At that time, magnetic/magnetooptic improvement of EuO-Al2O3-SiO2 glasses could be expected by incorporating divalent transition metal ions M2+ such as Co2+ and Fe2+ ions. In this paper, we report magnetic and optical properties of 70EuAl2O4-30SiO2 glasses doped with Co2+ or Fe2+ ions. Faraday rotation effects of these glasses are also presented. Conclusively, it is revealed that the ferromagnetic couplings of the dimmer Eu2+ ↑ -Fe2+ ↑ and the trimer Eu2+ ↑ -Co2+ ↑ -Eu2+ ↑ formed in the glasses enhance Faraday Rotation effects.