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TADASHI HASEGAWA,TAKESHI AKASAKA,YUTAKA MAEDA,MASAHIRO HASHIMOTO,MAKOTO KANDA,TAKAHIRO TSUCHIYA,TAKATSUGU WAKAHARA,YUHEI MIYAUCHI,SHIGEO MARUYAMA,JING LU,SHIGERU NAGASE 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2007 NANO Vol.2 No.4
Single-walled carbon nanotubes (SWNTs) synthesized by catalytic decomposition of an alcohol were purified by extraction. The purified SWNTs were characterized on the basis of visible-near infrared (vis-NIR) absorption, photoluminescence and Raman spectroscopic analyses, scanning electron microscopy (SEM) observation, and thermal analysis. Selective extraction of metallic nanotubes was also achieved by the extraction condition.
STEREOCHEMISTRY IN LONG-CHAIN BIRADICAL CYCLIZATION
Hasegawa, Tadashi,Yamazaki, Yuko,Yoshioka, Michikazu Korean Society of Photoscience 1997 Journal of Photosciences Vol.4 No.1
The structures of 8-membered azalactone isomers produced from photocyclization of 2-(N,N-dibenzylamino)ethyl benzoylacetate were determined by the X-ray structure analysis to clarify the stereochemical behavior of a 1,8-biradical. The remarkable stereoselectivity in cyclization of the 1,8-biradical to form cis- and trans-isomers of the azalactone was not observed. The ring conformations were boat-chair like and dihedral angles between C$_5$- and C$_6$- phenyl groups were ca 45$\circ$ in the both isomers. The 1,8-biradicals in the transition state for the cyclization would have nearly same boat-chair like conformation and twisted configuration with the dihedral angle of ca 45$\circ$ as the corresponding isomer, and this is responsible for luck of stereoselectivity in long-chain biradical cyclization.
Hasegawa, Tadashi,Yamazaki, Yuko,Yoshioka, Michikazu Korean Society of Photoscience 1997 Journal of Photosciences Vol.4 No.2
The model based on the idea that the p$_y$-orbital of the carbonyl oxygen is responsible to receiving hydrogen was devised for simulation of intramolecular hydrogen transfer. A Monte Carlo method was applied to free rotation of a molecular chain performed by changing the dihedral angles, and a "hit" was defined as the case when the migrating hydrogen comes within the region defined as the p$_y$-orbital and satisfies all the geometrical requirements for abstraction. A set of parameters was employed for defining the region and the requirements; $\tau$ was defined as the angle formed between O...H vector and its projection on the mean plane of the carbonyl group (- 43$\circ$ < $\tau$ < + 43$\circ$), $\Delta$ as the C=O...H angle (90 -15$\circ$ < $\Delta$ < 90 + 15$\circ$), $\theta$ as the O...H - C angle ( 180 - 80$\circ$< 0 < 180 + 80$\circ$), d as the distance from the center of the lobe of the p$_y$-orbital to hydrogen (0 < d < 1.04 ${\AA}$). The minimum value for the distance between carbonyl oxygen (O$_1$) and the migrating hydrogen (H$_i$) and for that between non-bonded atoms except the pair of O$_1$ and H$_i$ were assumed to be 0.52 ${\AA}$ and 1.54 ${\AA}$, respectively. The apphcation of this model to intramolecular $\beta$-, $\gamma$-, $\delta$-, $\epsilon$-, and $\zeta$-hydrogen abstraction in ketones and $\eta$- and $\theta$- proton transfer in oxoesters gave good results reflecting their photochemical behavior. The model was also used for prediction of photoreactivities of 2-(N,N-dibenzylamino)ethyl 2-, 3- and 4-benzoylbenzoate (1a - c). (1a - c).
Hasegawa, Takuya,Kim, Sun Woog,Ueda, Tadaharu,Ishigaki, Tadashi,Uematsu, Kazuyoshi,Takaba, Hiromitsu,Toda, Kenji,Sato, Mineo The Royal Society of Chemistry 2017 Journal of Materials Chemistry C Vol.5 No.36
<▼1><P>A novel red emitting, Ce<SUP>3+</SUP>-activated Sr3Sc4O9 phosphor were discovered, and its luminescent properties were investigated.</P></▼1><▼2><P>Most conventional white light emitting diodes (white-LEDs) that are widely used as a new lighting system in next generation lights with Y3Al5O12:Ce<SUP>3+</SUP> (YAG:Ce<SUP>3+</SUP>)-based phosphors have a low colour rendering index (CRI) because the YAG:Ce<SUP>3+</SUP> phosphor shows a weak emission intensity in the red spectral region. Therefore, discovering a red-emitting phosphor with a high-efficiency is quite important to enhance the CRI of white-LEDs. In this study, we successfully discovered a novel, red-emitting Ce<SUP>3+</SUP>-activated Sr3Sc4O9 phosphor that can be excited by blue-light irradiation at 425 nm. A crystal structure of the host material was first determined by Rietveld refinement, which indicated that it should be isostructural with Ba3Ln4O9 (Ln = Sc, Y and Dy-Lu). As the Ce<SUP>3+</SUP> content increased, the X-ray diffraction patterns shifted to a lower angle, which suggested that the Ce<SUP>3+</SUP> ion could substitute Sc in the Sr3Sc4O9 host. Under UV and blue-light excitation, the Ce<SUP>3+</SUP>-activated Sr3Sc4O9 phosphor exhibited a broad emission band with a maximum peak at 620 nm, and its full width half maximum (FWHM) was 180 nm (4530 cm<SUP>−1</SUP>). The highest emission intensity was obtained for Sr3(Sc0.997Ce0.003)4O9, and the internal quantum efficiency of this phosphor under excitation at 425 nm was 53%. To the best of our knowledge, the emission band of the Ce<SUP>3+</SUP>-activated Sr3Sc4O9 phosphor is the longest wavelength for a reported Ce<SUP>3+</SUP>-activated oxide phosphor.</P></▼2>
김선욱,Takuya Hasegawa,Hiroyuki Yumoto,Tadashi Ishigaki,Kazuyoshi Uematsu,Kenji Toda,Mineo Sato 한양대학교 세라믹연구소 2014 Journal of Ceramic Processing Research Vol.15 No.3
Rare earth-free white emitting (Sr,Sn)(Zn,Mn)P2O7 phosphors were synthesized in a single phase form by a conventional solidstate reaction method and photoluminescent properties were characterized. These phosphors showed three broad band in emission spectra at 340, 440, and 690 nm, and the ratio of emission intensity between blue-green light and red light changes with Mn2+ content increasing because of energy transfer from Sn2+ to Mn2+. The emission color of the phosphors varied from blue-white to orange-white with the increase in the Mn2+ content and the emission color of the (Sr0.90Sn0.10)(Zn0.97Mn0.03)P2O7 phosphor was very close to white light.
Synthesis of blue-emitting (K1−xNax)Mg4(PO4)3:Eu2+ phosphors
김선욱,Takuya Hasegawa,Tadashi Ishigaki,Kazuyoshi Uematsu,Mineo Sato,Kenji Toda 한국정보디스플레이학회 2014 Journal of information display Vol.15 No.2
Blue-emitting (K1−xNax)Mg4(PO4)3:Eu2+ phosphors were synthesized through a conventional solid-state reaction method, and their photoluminescence properties were characterized. These phosphors exhibited the typical emission band assigned to the transition from 4f65d1 to 4f7 of Eu2+, and the emission intensity was effectively enhanced by Na+-doping into the host lattice. The highest blue emission peak intensity was obtained for (K0.65Na0.35)Mg4(PO4)3:1 mol%Eu2+, where the relative emission peak intensity was 33% of that for the commercial blue-emitting BaMgAl10O17:10 mol%Eu2+ phosphor. In addition, these phosphors have excellent thermal stability in the temperature quenching effect.
INTERACTION OF SINGLE-WALLED CARBON NANOTUBES WITH AMINE
YUTAKA MAEDA,MICHIO YAMADA,TADASHI HASEGAWA,TAKESHI AKASAKA,JING LU,SHIGERU NAGASE 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2012 NANO Vol.7 No.1
Single-walled carbon nanotubes (SWNTs) have excellent mechanical and electrical properties that have led to the proposal of many potential applications. However, SWNTs are typically grown as bundles of metallic and semiconducting tubes. This prevents their widespread application. Therefore, it is technologically critical to disperse and purify SWNTs and separate metallic and semiconducting SWNTs effectively. Recent progress and advances have been made on dispersion, separation, assemble, and control of electronic property of SWNTs by the interaction of organic molecules. This paper presents a brief review of the interaction of SWNTs with amine.
C60(OH)n-ASSISTED DISPERSION OF SINGLE-WALLED CARBON NANOTUBES
YUTAKA MAEDA,TAKAAKI KATO,JUNKI HIGO,TADASHI HASEGAWA,TAKAHIRO KITANO,TAKAHIRO TSUCHIYA,TAKESHI AKASAKA,TOSHIYA OKAZAKI,JING LU,SHIGERU NAGASE 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2008 NANO Vol.3 No.6
We demonstrate that C60(OH)n-assists the dispersion of SWNTs in aqueous and nonaqueous solutions, which effectively exfoliates large-diameter SWNTs. The SWNT dispersions are characterized by absorption and photoluminescence spectra.
Development of Water Assisted Solid State Reaction for the Ceramic Materials
Toda, Kenji,Kim, Sun Woog,Hasegawa, Takuya,Watanabe, Mizuki,Kaneko, Tatsuro,Toda, Ayano,Yamanashi, Ryota,Kumagai, Shota,Muto, Masaru,Itadani, Atsushi,Sato, Mineo,Uematsu, Kazuyoshi,Ishigaki, Tadashi,K Trans Tech Publications, Ltd. 2017 Key Engineering Materials Vol.751 No.-
<P>We report a novel soft chemical synthesis method, water assisted solid state reaction (WASSR) method. This method is very simple and can synthesize many ceramic materials just by storing or mixing raw materials added a small amount of water in a reactor at low temperature below 373 K. For example, well-crystalline SrMoO4 was obtained using the WASSR method.</P>
Kim, Sun Woog,Toda, Kenji,Hasegawa, Takuya,Watanabe, Mizuki,Kaneko, Tatsuro,Toda, Ayano,Itadani, Atsushi,Sato, Mineo,Uematsu, Kazuyoshi,Ishigaki, Tadashi,Koide, Junko,Toda, Masako,Kudo, Yoshiaki,Masak American Scientific Publishers 2018 Science of advanced materials Vol.10 No.4
<P>Lithium orthophosphate Li3PO4 nanoparticles were synthesized through a water assisted solid state reaction (WASSR) method. The nanoparticles obtained in this study adopt a stable orthorhombic structure (beta-type), which is a low temperature phase, in a single phase with high crystallinity. The Li3PO4 nanoparticles have a granular particle morphology and the particle size is less than 50 nm.</P>