Yutaka Kaihatsu

Novel rare-earth-free tunable-color-emitting BCNO phosphors

We present a facile synthesis of novel, rare-earth (RE)-ion-free boron carbon oxynitride (BCNO) phosphors. The preparation method, chemical composition, luminescent properties and emission mechanisms, as well as current trends in BCNO phosphors are reviewed. The novel BCNO phosphors were synthesized from inexpensive and environmentally friendly raw materials by a straightforward route using liquid precursors at low temperatures under atmospheric pressure. The newly developed BCNO phosphors demonstrated tunable color emission, high quantum efficiency, and long-duration afterglow. The color emission of these phosphors can be tuned across almost the entire visible light spectrum by varying the molar ratios of the raw materials.

Fabrication and Characterization of a Yellow-Emitting BCNO Phosphor for White Light-Emitting Diodes

A yellow-emitting phosphor comprised of boron, carbon, nitrogen, and oxygen (BCNO) atoms without any rare-earth ions as luminescence centers was successfully synthesized using a facile process at low temperature and atmospheric pressure. The synthesized BCNO powders showed a broad emission spectrum centered at 540 nm under excitation at 460 nm due to the radiation transitions of local 2 H g → 1 Σ - g luminescence provided in the BO - 2 species. Further analysis revealed that the BCNO yellow phosphor exhibited a high external quantum efficiency (60%) having a hexagonal-BN crystalline structure mixed with cubic-B 2 O 3 . The synthesized yellow-emitting BCNO phosphor is promising for high-efficiency phosphor conversion-based white light-emitting diodes.

Effect of the Carbon Source on the Luminescence Properties of Boron Carbon Oxynitride Phosphor Particles

The effect of the carbon source on the optimization of the photoluminescence (PL) performance of boron carbon oxynitride (BCNO) phosphor particles was systematically investigated. Ethylene glycol, tetraethylene glycol (TEG), and poly(ethylene glycol) of various Mw values were used as the organic sources. When TEG was used, the BCNO phosphors exhibited high PL performance under excitation at 365 nm with a quantum efficiency of up to 60%. The emission spectrum peak of the prepared BCNO particles was affected by the Mw of the carbon sources. An additional study investigated in detail the effects of the carbon/boron and nitrogen/boron molar ratios on PL properties. The emission spectra with a wavelength peak ranging from 380 nm (near UV) to 570 nm (near red) could be adjusted by varying the carbon/boron or nitrogen/boron ratios.

Controllable Mesopore-size and Outer Diameter of Silica Nanoparticles Prepared by a Novel Water/Oil-Phase Technique

Tunable pore size and outer particle diameter of spherical mesoporous silica particles in the nanometer range were successfully synthesized using a novel water/oil-phase synthesis technique. This method involves (i) simultaneous hydrolytic condensation of tetraorthosilicate to form silica and polymerization of styrene into polystyrene (PS), (ii) self-assembly nanocluster silica and nanocluster PS to form silica/PSL nanoparticle, and (iii) calcination process to remove organic components and to produce mesoporous silica particle. In this study, an amino acid (e.g. lysine) was utilized to catalyze and to maintain the silica formation due to its ability in covering prepared silica after reaction. Further, another advantage of this catalyst is more harmless than other catalysts (e.g. ammonia, N 2 H 4 ). The result showed spherical particles with controllable pore size (from 4 to 15 nm) and outer diameter (from 20 to 80 nm) was produced. The ability to control pore size and outer diameter was drastically altered by adjusting the concentration of styrene and hydrophobic molecules, respectively. After the preparation of particle was understood clearly, the large-molecule-adsorption performance of the prepared porous particles was conducted. As expected, relatively large organic molecules (i.e. Rhodamine B) were well-absorbed in the prepared sample but not by the commercial non-porous particles. With this reason, the prepared mesoporous silica particles may be used efficiently in various applications, including electronic devices, sensors, pharmaceuticals, and environmentally sensitive pursuits, due to its harmless process, compatibility for bio-application, and excellent adsorption properties.