• Title/Summary/Keyword: CE

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ARPES Study of Quasi-Two Dimensional CDW System CeTe2 (준이차원 전하밀도파 CeTe2의 각분해 광전자 분광 연구)

  • Kim, D.H.;Lee, H.J.;Kang, J.S.;Kim, H.D.;Min, B.H.;Kwon, Y.S.;Kim, J.W.;Min, B.I.
    • Journal of the Korean Magnetics Society
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    • v.20 no.5
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    • pp.173-177
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    • 2010
  • The electronic structure of charge-density-wave (CDW) system $CeTe_2$ has been investigated by using angle-resolved photoemission spectroscopy (ARPES). The clearly dispersive band structures are observed in the measured ARPES spectra, indicating the good quality of the single-crystalline sample employed in this study. The four-fold symmetric patterns are observed in the constant energy (CE) mappings, indicating the $2{\times}2$ lattice deformation in the Te(1) sheets. The observed CE images are similar to those of $LaTe_2$, suggesting that Ce 4f states have the minor contribution to the CDW formation in $CeTe_2$. This study reveals that the carriers near the Fermi level should have mainly the Te(1) 5p and Ce 5d character, that the Te(1) 5p bands contribute to the CDW formation, and that the Ce 5d bands cross the Fermi level even in the CDW state.

A Study on the Luminescence Properties of LiGd9(SiO4)6O2:Ce3+ (LiGd9(SiO4)6O2:Ce3+ 형광 특성 연구)

  • Jin, Seongjin
    • Journal of the Korean Society of Radiology
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    • v.9 no.3
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    • pp.169-174
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    • 2015
  • $LiGd_9(SiO_4)_6O_2:Ce^{3+}$ phosphors were synthesized by solid-state reaction method. The structural characteristic was investigated by X-ray powder diffraction analysis. The emission and excitation spectra of the $Ce^{3+}$ ions doped $LiGd_9(SiO_4)_6O_2$ phosphors were obtained under the UV excitation. The emission spectra of $LiGd_9(SiO_4)_6O_2:Ce^{3+}$ shows the band at 410 nm corresponding to the $^2F_{5/2}$ and $^2F_{7/2}$ states of $Ce^{3+}$. The red shift of $Ce^{3+}$ emission is found as the $Ce^{3+}$ concentration increases, which could be explained by the change in crystal-field symmetry and strength with increasing $Ce^{3+}$ concentration. Fluorescence decay time of $Ce^{3+}$ was about 20 ns. When the concentration of $Ce^{3+}$ increases life time was slightly reduced.

The study on the dry etching characteristics of $CeO_2$ thin films ($CeO_2$ 박막의 건식 식각 특성 연구)

  • Oh, Chang-Seck;Kim, Chang-Il
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2001.05b
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    • pp.84-87
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    • 2001
  • In this study, $CeO_2$ thin films were etched with a $CF_4/Ar$ gas combination in inductively coupled plasma (ICP), The maximum etch rate of $CeO_2$ thin films is $270{\AA}/min$under $CF_4/(CF_4+Ar)$ of 0.2, 600 W/-200 V, 15 mTorr, and $25^{\circ}C$. The selectivities of $CeO_2$ to PR and SBT are 0.21, 0.25. respectively. The surface reaction of the etched $CeO_2$ thin films was investigated with x-ray photoelectron spectroscopy (XPS). There is a chemical reaction between Ce and F, Compounds such as $Ce-F_x$ are remains on the surface of $CeO_2$ thin films. Those products can be removed by Ar ion bombardment effect, The results of secondary ion mass spectrometer (SIMS) were equal to these of XPS. Scanning electron microscopy (SEM) was used to examine etched profiles of $Ce-F_x$ thin films. The etch profile of over-etched $CeO_2$ films with the $0.5 {\mu}m$ line was approximately $65^{\circ}$.

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Li-doped Y2SiO5:Ce, Blue-emitting Phosphor (Li-이온이 도핑된 Y2SiO5:Ce 청색 형광체)

  • Park, Jung-Cheol;Jeon, Gi-Wan
    • Journal of the Korean Chemical Society
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    • v.50 no.3
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    • pp.232-236
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    • 2006
  • The Y1.99-xMxCe0.01SiO5(M=Li, La, Nd, and Gd) phosphors were synthesized by solid-state reaction at 1350oC for 10h under reducing atmosphere in order to improve properties of blue emitting phosphors. Compared with commercial blue phosphors, the Y2SiO5:Ce blue phosphors substituted with various elements showed significant enhancement of the emission intensity. Particularly, 1 mol% Li doped Y2SiO5:Ce phosphors indicated the maximum emission intensity in the photoluminescence spectra. Thanks to SEM analyses revealed that the morphology of Y2SiO5:(Ce,Li) blue phosphors was a pseudo-spherical with particle size of 3m.

3원계 U-Ce-O의 소결 Kinetics 연구

  • Kim, Hyeong-Su;Park, Chun-Ho;Bae, Gi-Gwang;Jeong, Sang-Tae;Choe, Chang-Beom
    • Korean Journal of Materials Research
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    • v.3 no.3
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    • pp.276-281
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    • 1993
  • In order to study the sintering kinetics of the ternery system, U-Ce-O, its shrinkage rate with time and temperature at the Ar atmoshpere were measured by using the dilatometer. At the sintering kinetics of U-Ce-O, sintering rate curve revealed bimodal and the first extreme point at bimodal curve was affected by the $UO_2$ the second one was due to the $CeO_2$. The sintering of $(U, Ce)O_2$ was delayed as increasing the $CeO_2$. At the same lOwt. % content, the highest sintering rate was observed at the $(U, Ce)O_2$ sample ball-milled for 4 hours.

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Ce $L_Ⅲ$-edge X-ray Absorption Spectroscopic Studies on the Tetrameric Ce-polyoxyhydroxy Cation Intercalated Aluminosilicate

  • Yun, Ju Byeong;Hwang, Seong Ho;Kim, Dong Guk;Gang, Seong Gu;Choe, Jin Ho
    • Bulletin of the Korean Chemical Society
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    • v.21 no.3
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    • pp.305-309
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    • 2000
  • The cerium ion intercalated aluminosilicate was prepared by ion exchange reaction between $Na^+$ in montmorillonite and $Ce^{+4}$ in aqueous solution. The X-ray absorption near edge structrure(XANES) analyses indicate that the $Ce^{+4}$ ions are partially reduced to the $Ce^{+3}$ ones during the intercalation into layered aluminosilicate due to a charge transfer between host and intercalant. From the EXAFS analysis, two different (Ce-O) bonding pairs could be characterized with the distances and coordination numbers of 2.31 $({\pm}0.02){\AA}$ ${\times}$ 8.2 $({\pm}1.5)$ and 2.66 $({\pm}0.02){\AA}$ ${\times}$ 2.7 $({\pm}1.0)$, respectively, with the oxygen atoms as the first nearest neighbor, and two (Ce-Ce) pairs at 3.78 ${\AA}$ as the second neighbor. It is therefore concluded that the most probable Ce-species stabilized in the interlayer space of aluminosilicate after the intercalation is the tetrameric Ce-polyoxy/hydorxy cations with the mixed valent state of 0.75 $Ce^{+4}$.0.25 $Ce^{+3}$.

Preparation and Characterization of Ceria Stabilized Tetragonal Zirconia Polycrystals(I) : Effect of CeO2 Contents on the Mechanical Properties of Ce-TZP (세리아 안정화 지르코니아의 제조 및 특성(I) : CeO2첨가량 변화에 따른 Ce-TZP의 기계적 특성)

  • Jung, Seung-Hwa;Kang, Jong-Bong
    • Korean Journal of Materials Research
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    • v.20 no.7
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    • pp.379-384
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    • 2010
  • The usual ceramic process of mixing and milling in state of oxides $ZrO_2$ and $CeO_2$ was adopted in this study in a wet process to manufacture Ce-TZP. $CeO_2$-$ZrO_2$ ceramics containing 8~20 mol% $CeO_2$ were made by heat treatment at $1250\sim1500^{\circ}C$ for 5hr. The maximum dispersion point of every slurry manufactured with a mixture of $ZrO_2$ and $CeO_2$ was neat at pH10. A stable slurry with average particle size of 90 nm can be manufactured when it is dispersed with the use of ammonia water and polycarboxylic acid ammonium. The sintered Ce-TZP ceramics manufactured with the addition of $CeO_2$ in a concentration of less than 10 mol% progressed to the fracture of the specimen due to the existence of a monoclinic phase of more than 30% at room temperature. More than 99% of the tetragonal phase was created for the sintered body with the addition of $CeO_2$ beyond 18 mol%, but the degradation of the mechanical properties on the entire specimen was brought about due to the $CeO_2$ existing in a percentage above 3%. Consequently, the optimal Ce-TZP level combined in the oxide state was identified to be 16 mol% of $CeO_2$ contents.

Synthesis and luminescence properties of $Sr_{1-x}Ca_xGa_2S_4:Ce,Na$ phosphors ($Sr_{1-x}Ca_xGa_2S_4:Ce,Na$ 형광체의 합성과 발광 특성)

  • Sung, Hye-Jin;Huh, Young-Duk
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.16 no.6
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    • pp.267-272
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    • 2006
  • A series of $Sr_{1-x}Ca_xGa_2S_4:Ce,Na$ phosphors have been synthesized by solid-state reaction. The photoluminescence and structural properties of $Sr_{1-x}Ca_xGa_2S_4:Ce,Na$ have been examined. The $Sr_{1-x}Ca_xGa_2S_4:Ce,Na$ phosphors have a strong absorption at 400 nm, which is the emission wavelength of a violet light emitting diode (LED). The emission peaks of $SrGa_2S_4:Ce,Na$are located at 448 nm and 485 nm. The partial replacement of Sr by Ca in $Sr_{1-x}Ca_xGa_2S_4:Ce,Na$ causes a red shift of emission wavelengths. The $Sr_{1-x}Ca_xGa_2S_4:Ce,Na$ can be used as blue emitting phosphors pumped by the violet LED for fabricating the multi-band white LED.

Texture Development of CeO2 Buffer Layer and its Effect on Superconducting MOD-YBCO Films (CeO2 완충층의 결정성장 특성 및 금속 유기물 증착법으로 제조된 초전도 YBCO층에 미치는 영향)

  • Chung, Kook Chae;Kim, Y.K.;Wang, X.L.;Dou, S.X.
    • Korean Journal of Metals and Materials
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    • v.47 no.10
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    • pp.681-685
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    • 2009
  • $CeO_2$ buffer layers have been deposited on YSZ single crystal substrates via a radio-frequency sputtering method. We focused on the texture development of $CeO_2$ with out-of-plane alignment and its effects on a superconducting YBCO layer, which was deposited by metal organic deposition. $CeO_2$ layers were grown epitaxially on single crystal YSZ substrates and subsequent YBCO layers were also grown epitaxially from $CeO_2$ layers. It was observed that the intensity of $CeO_2$(200) decreased with deposition temperature. ${\theta}-2{\theta}$ scan FWHM values of $CeO_2$(200) were inversely proportional to the peak intensities of $CeO_2$(200). The sample with the lowest $CeO_2$(200) intensity and poor out-of-plane alignment showed a strong reaction with the MOD-YBCO layer resulting in a thicker $BaCeO_3$ layer. The texture and superconducting property of the YBCO layer were affected indirectly by the formation of a $BaCeO_3$ layer at the interface between the $CeO_2$ and YBCO layers.