Hiroshi Okura

A microfluidic device fully integrated with three pH sensing electrodes and passive mixer for nanoparticle synthesis

We have proposed a novel microfluidic device for nanoparticle synthesis which is integrated with a pH sensing electrode array for in situ real time pH monitoring and a passive mixer for effective reaction of two chemical fluids within a small scaled microfluidic device. The passive mixer is fabricated with three glass substrates and the mixing channel is designed 3 dimensionally to maximize the mixing efficiency. Moreover, our pH sensing is achieved with three electrodes measurement method. The three electrodes are working electrode of IrO2, counter electrode of Pt and reference electrode of Ag/AgCl, which are fabricated by lift-off process on a silicon substrate. By the anodic bonding of the Si substrate having pH sensing electrode array to the glass substrates having passive mixer, we have accomplished the microfluidic device fabrication. The liquid junction between the flow channel and KCl solution chamber for reference electrode is realized by pores created at both sides of dummy metal layer of Pt during the anodic bonding process. We have performed pH measurement and mixing experiment as well. As a result, we have verified the performance of our microfluidic device.

X-ray Absorption Fine Structure Analysis of Valence State of Ce in Y3Al5O12:Ce Phosphor Synthesized by Coprecipitation Method

To clarify the activation procedure of Ce through the synthesis of Y3Al5O12:Ce (YAG:Ce) phosphor by a coprecipitation method, the valence state of Ce has been studied by X-ray absorption fine structure (XAFS) analysis. A linear combination of reference spectra was fit to the X-ray absorption near-edge structure (XANES) and the extended XAFS (EXAFS) oscillation curves of the oxidized samples. It was found that YAG and CeO2 are formed above 1000 °C. The fitting result indicates that Ce atoms with a concentration of about 0.6 mol % are directly incorporated into the YAG lattice upon oxidation at above 1000 °C without their segregation as CeO2. The incorporated Ce3+ ions are considered to be uniformly distributed in the YAG particles and act as efficient luminescent centers.

Silica-coating of quantum nanorods by a sol–gel process and their photo-bleaching properties

AbstractThis paper describes silica-coating of rod-structured nanoparticles composed of cadmium compounds, or quantum rods (QR), by means of a sol–gel method. QRs surface-modified with polyethyleneimine (PEI) (QR/PEI) had an average lateral size of 6.7 ± 0.9 nm and an average longitudinal size of 24.4 ± 2.5 nm. Silica-coated QR nanoparticles (QR/SiO2) were fabricated with a sol–gel process using water, sodium hydroxide, and tetraethylorthosilicate in ethanol in the presence of the QR/PEI nanoparticles. The QR/SiO2 nanoparticles were core-shell particles composed of the QRs as the core, the PEI as the matrix, and the silica as the shells. The colloid solution of QR/SiO2 nanoparticles showed more stable fluorescence to aging in a dark box in atmosphere at room temperature than that of QR/PEI nanoparticles.