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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>
Hirotaka Hasegawa,Masahiro Shin,Jun Kawagishi,Hidefumi Jokura,Toshinori Hasegawa,Takenori Kato,Mariko Kawashima,Yuki Shinya,Hiroyuki Kenai,Takuya Kawabe,Manabu Sato,Toru Serizawa,Osamu Nagano,Kyoko Ao 대한뇌졸중학회 2022 Journal of stroke Vol.24 No.2
Background and Purpose To assess the long-term outcomes of intracranial dural arteriovenous fistula (DAVF) treated with stereotactic radiosurgery (SRS) alone or embolization and SRS (Emb- SRS) and to develop a grading system for predicting DAVF obliteration. Methods This multi-institutional retrospective study included 200 patients with DAVF treated with SRS or Emb-SRS. We investigated the long-term obliteration rate and obliteration-associated factors. We developed a new grading system to estimate the obliteration rate. Additionally, we compared the outcomes of SRS and Emb-SRS by using propensity score matching. Results The 3- and 4-year obliteration rates were 66.3% and 78.8%, respectively. The post-SRS hemorrhage rate was 2%. In the matched cohort, the SRS and Emb-SRS groups did not differ in the rates of obliteration (P=0.54) or post-SRS hemorrhage (P=0.50). In multivariable analysis, DAVF location and cortical venous reflux (CVR) were independently associated with obliteration. The new grading system assigned 2, 1, and 0 points to DAVFs in the anterior skull base or middle fossa, DAVFs with CVR or DAVFs in the superior sagittal sinus or tentorium, and DAVFs without these factors, respectively. Using the total points, patients were stratified into the highest (0 points), intermediate (1 point), or lowest (≥2 points) obliteration rate groups that exhibited 4-year obliteration rates of 94.4%, 71.3%, and 60.4%, respectively (P<0.01). Conclusions SRS-based therapy achieved DAVF obliteration in more than three-quarters of the patients at 4 years of age. Our grading system can stratify the obliteration rate and may guide physicians in treatment selection.
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.
Novel yellowish white-emitting Eu2+-activated phosphate phosphor based on Rb2Ba3P4O14
Kazuma Sugimoto,Takuya Hasegawa,김선욱,Kazuyoshi Uematsu,Kenji Toda,Mineo Sato 한양대학교 세라믹연구소 2016 Journal of Ceramic Processing Research Vol.17 No.5
Eu2+-doped Rb2Ba3P4O14 phosphors were synthesized in a single phase form by a conventional solid state reaction method andtheir optical properties were characterized. These phosphors showed broad optical absorption bands that can cover the UVand near-UV region, and exhibited a narrow deep-blue emission and broad reddish-yellow emission with peaks at 423 nm and550 nm, respectively. The highest reddish-yellow emission intensity was obtained for Rb2(Ba0.99Eu0.01)3P4O14.
Park, Jae-Hong,Hasegawa, Takuya,Senbu, Osamu,Park, Dong-Cheon Korea Concrete Institute 2012 International Journal of Concrete Structures and M Vol.6 No.3
In order to predict the neutralization of concrete which is the reaction of carbonation dioxide from the outside and cement hydration product, such as calcium hydroxide and C-S-H, it was studied the numerical analysis method considering change of the pore structure and relative humidity during the neutralization reaction. Diffusion-reaction neutralization model was developed to predict the neutralization depth of concrete with coating finishing material. In order to build numerical analysis models considering outdoor environment and finishing materials, the adaption of proposed model was shown the results of existing outdoor exposure test results and accelerated carbonation test.
Jae-Hong Park,Takuya Hasegawa,Osamu Senbu,Dong-Cheon Park 한국콘크리트학회 2012 International Journal of Concrete Structures and M Vol.6 No.3
In order to predict the neutralization of concrete which is the reaction of carbonation dioxide from the outside and cement hydration product, such as calcium hydroxide and C?S?H, it was studied the numerical analysis method considering change of the pore structure and relative humidity during the neutralization reaction. Diffusion?reaction neutralization model was developed to predict the neutralization depth of concrete with coating finishing material. In order to build numerical analysis models considering outdoor environment and finishing materials, the adaption of proposed model was shown the results of existing outdoor exposure test results and accelerated carbonation test.
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>
Novel Soft Chemical Synthesis Methods of Ceramic Materials
Toda, Kenji,Kim, Sun Woog,Hasegawa, Takuya,Watanabe, Mizuki,Kaneko, Tatsuro,Toda, Ayano,Itadani, Atsushi,Sato, Mineo,Uematsu, Kazuyoshi,Ishigaki, Tadashi,Koide, Junko,Toda, Masako,Kudo, Yoshiaki,Masak Trans Tech Publications, Ltd. 2016 Key Engineering Materials Vol.690 No.-
<P>We report novel soft chemical synthesis method, solid hydratethermal reaction (SHR) method as a new soft chemistry. This method is very simple and can synthesize the ceramic materials just by storing the mixture of raw materials added a small amount of water in a reactor at low temperature below 373 K. For example, nanosize YVO4 (under 100 nm in diameter) was obtained using the SHR method.</P>