Papers by Author: Hiromichi Takebe

Abstract: We investigated epitaxial assembly in aggregates of CaTiO3 nanoparticles, which were synthesized under a hydrothermal condition at 150°C using water/ethanol solvent, by transmission electron microscopy analysis combined with a three-dimensional tomography technique. The obtained results indicate that epitaxial assembly is involved in the crystal growth of CaTiO3 nanoparticles, and that in aggregates of CaTiO3 nanoparticles epitaxial assembly occur on their {101} planes.

Abstract: Nanosized Y2O3:Eu3+ crystalline powders with average particle sizes around 100 nm, measured by field-emission scanning electron microscopy (FE-SEM), have been synthesized by a polymerized precursor method using carboxymethyl cellulose (CMC). The nanocrystalline phosphors exhibit intense photoluminescence (PL) and cathodoluminescence (CL) around 612 nm, being attributed to the 5D0-7F2 transition of Eu3+. Electroluminescence (EL) properties of the nanophosphors in the form of thick films were investigated, and emission of red light with maximum intensity at 612 nm (corresponding to x = 0.57 and y = 0.32 in the CIE chromaticity diagram) was observed under high ac field at 1 kHz. The obtained results suggest a possibility that Y2O3:Eu3+ nanopowders can be used as a red-emitting phosphor for EL devices.

Abstract: An investigation has been made on the state of barium titanate (BaTiO3; BTO, hereafter) nanoparticles of 10-15 nm in diameter dispersed in various suspension media, such as 2-methoxyethanol (ethylene glycol monomethyl ether: EGMME) with and without acetylacetone (Acac), ethanol, and isopropanol. The state of the nanoparticles dispersed in these suspension media is deduced from the behavior pattern of their optical transmittance (T), in the wavelength (λ) range of 300-900 nm; the concentration (c) of BTO nanoparticles in the suspensions was varied from 0.01 to 0.25 mol/L. T-c plots obtained for EGMME+Acac and EGMME suspensions at various wavelengths indicate that BTO nanoparticles take two and three different states in the suspensions, respectively, from mono-dispersed to agglomerated states with increasing c.