• Title/Summary/Keyword: $BaWO_4$

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Luminescent Properties and Energy Transfer Efficiency of BaWO4:Dy3+, Eu3+ White Light-Emitting Phosphors (BaWO4:Dy3+,Eu3+ 백색광 형광체의 발광 특성과 에너지 전달 효율)

  • Cho, Shinho
    • Journal of the Korean institute of surface engineering
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    • v.54 no.3
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    • pp.112-118
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    • 2021
  • Dy3+- and Eu3+-codoped BaWO4 phosphors for white light-emitting diode were synthesized with different activator ions via a solid-state reaction process. The structural, morphological, and optical properties of the BaWO4:Dy3+,Eu3+ phosphors were investigated as a function of Eu3+ concentration at a fixed concentration of Dy3+ ions. XRD patterns exhibited that all the synthesized phosphors had a tetragonal system, irrespective of the concentrations of Dy3+ and Eu3+ ions. The excitation spectra of the synthesized phosphors were composed of three intense bands centered at 251, 355, and 393 nm and several weak peaks. For the BaWO4:Dy3+,Eu3+ phosphors synthesized with 1 mol% of Eu3+, the emission spectra under ultraviolet excitation at 393 nm showed two strong blue and yellow bands at 485 and 577 nm corresponding to the 4F9/26H15/2 and 4F9/26H13/2 transitions of Dy3+ ions, respectively and several weak bands in the range of 600-700 nm resulting from the 4f transitions of Eu3+ ions. As the concentration of Eu3+ ions increased, intensities of the blue and yellow emission bands gradually decreased while those of the red emissions increased rapidly and the energy transfer efficiency from Dy3+ to Eu3+ ions was 95.3% at 20 mol% of Eu3+. The optimum white light emission with x=0.363, y=0.357 CIE 1931 chromaticity coordinates was obtained for the sample doped with 5 mol% Dy3+ and 1 mol% of Eu3+.

Effect of Annealing Temperature on the Properties of BaWO4:Eu Thin Films deposited by RF Magnetron Sputtering (RF 마그네트론 스퍼터링으로 증착한 BaWO4:Eu 박막의 특성에 열처리 온도가 미치는 영향)

  • Jeong, U-Jin;Hwang, Su-Min;Park, Tae-Jun;Jang, Won-U;Kim, Chun-Su;Jo, Sin-Ho
    • Proceedings of the Korean Institute of Surface Engineering Conference
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    • 2012.11a
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    • pp.160-160
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    • 2012
  • 라디오파 마그네트론 스퍼터링 방법을 사용하여 유리 기판 위에 Eu 이온이 도핑된 $BaWO_4$ 박막을 성장 시킨 후에 온도 범위 $400{\sim}550^{\circ}C$에서 급속 열처리를 수행하였다. 박막의 결정 구조와 표면 형상은 각각 x-선 회절법과 주사전사현미경으로 조사였다. 급속 열처리 온도에 관계없이 모든 적색 형광체 박막은 622 nm에 피크를 갖는 적색 발광을 나타내었고, 열처리 온도가 $400^{\circ}C$에서 $550^{\circ}C$로 증가함에 따라 적색 발광 스펙트럼의 세기는 감소하는 경향을 보였다.

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Microwave Dielectric Properties of (Sr$_{1-x}$Bax)(Mg$_{1/3}$Nb$_{2/3}$)O$_3$ with SrWO$_4$ addition (SrWO$_4$가 첨가된 (Sr$_{1-x}$Bax)(Mg$_{1/3}$Nb$_{2/3}$)O$_3$의 마이크로파 유전특성)

  • Heo, Hoon;Park, Chan-Sik;Kim, Kyoung-Young;Byun, Jae-Dong
    • Journal of the Korean Ceramic Society
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    • v.36 no.3
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    • pp.325-331
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    • 1999
  • SrWO4가 첨가된 (Sr1-xBax)(Mg1/3Nb2/3)O3의 마이크로파 유전특성에 관하여 조사하였다. 관찰된 조성영역에서 Sr(Mg1/3Nb2/3)O3과 Ba(Mg1/3Nb2/3)O3은 (Sr1-xBax)(Mg1/3Nb2/3)O3고용체를 형성하고 SrWO4의 첨가는 고용체의 소결성을 향상시켜 소결온도 155$0^{\circ}C$에서 상대밀도 97% 이상을 얻었다. 소결한 시편의 EDS분석결과, SrWO4의 첨가량이 많은 시편에서 2차상이 존재하는 것을 알수 있었다. 순수한 Sr(Mg1/3Nb2/3)O3에 SrWO4를 0.01 mole첨가하여 1550~1$600^{\circ}C$에서 소결한 시편의 유전특성은 $\varepsilon$r 30, Q$\times$fo$\geq$55000,$ au$f -23 ppm/$^{\circ}C$이었다. 0.01 mole SrWO4가 첨가된 (Sr1-xBax)(Mg1/3Nb2/3)O3 고용체의 유전율과 온도계숙가 x에 따라 점차적으로 계속 증가하였고 Q$\times$fo는 x$\leq$0.25에서 x에 따라 감소하고 x$\geq$0.3에서 다시 증가하였다. (Sr0.65Ba0.35)(Mg1/3Nb2/3)O3+0.01SrWO4의 조성을 갖는 시편에서 $\varepsilon$r 34.4, Q$\times$fo$\geq$55000,$\tau$f 0 ppm/$^{\circ}C$이었다.

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A Study on the Effective Utilization of Intensifying Screens in the Region of Diagnostic Radiology (진단방사선 영역에서 증감지의 유효이용에 관한 연구)

  • Kim, Young-Keun;Lee, Kyung-Sup
    • Journal of radiological science and technology
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    • v.22 no.1
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    • pp.43-47
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    • 1999
  • In order to obtain effective utilization of intensifying screens[$CaWO_4(W),\;Gd_2O_2S:Tb(Gd)$, BaFCl : Eu(Ba)] over the diagnostic radiology range, we calculated absorption coefficient (${\mu}$), absorption efficiency (${\eta}_{\alpha}$) and absorbed energy ratio(R) and analyzed effects of these properties on X-ray image, finally concluded as below. Regardless of presence of contrast media, absorption coefficient of Gd the highest and decreased with increase of thickness and kVp. Absorption efficiency related with absorbance of fluorescent materials showed the highest value for the Gd, and discontinuous points exhibited at around $80{\sim}90\;kVp$ and $90{\sim}100kVp$ for the Ba and the Gd, respectively. Furthermore, the absorbed energy ratio(R) correspond to contrast of reflection showed the largest value for the W in the absence of contrast media, and for the Gd in the case of the existence of it, and the ratio was decreased with increasing of incident energy. Owing to these properties, we assumed that it was more preferable to use rare earth type intensifying screen for the radiography using in the C.M.(I, Ba), while in the general radiography, $CaWO_4$ intensifying screen was applicable.

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Synthesis and Luminescence Properties of Tb3+-Doped K2BaW2O8 Phosphors (Tb3+ 이온이 첨가된 K2BaW2O8 형광체의 합성 및 형광특성)

  • Jang, Kyoung-Hyuk;Koo, Jae-Heung;Seo, Hyo-Jin
    • Korean Journal of Materials Research
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    • v.22 no.9
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    • pp.489-493
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    • 2012
  • Green phosphors $K_2BaW_2O_8:Tb^{3+}$(1.0 mol%) were synthesized by solid state reaction method. Differential thermal analysis was applied to trace the reaction processes. Three endothermic values of 95, 706, and $1055^{\circ}C$ correspond to the loss of absorbed water, the release of carbon dioxide, and the beginning of the melting point, respectively. The phase purity of the powders was examined using powder X-ray diffraction(XRD). Two strong excitation bands in the wavelength region of 200-310 nm were found to be due to the ${WO_4}^{2-}$ exciton transition and the 4f-5d transition of $Tb^{3+}$ in $K_2BaW_2O_8$. The excitation spectrum presents several lines in the range of 310-380 nm; these are assigned to the 4f-4f transitions of the $Tb^{3+}$ ion. The strong emission line at around 550 nm, due to the $^5D_4{\rightarrow}^7F_5$ transition, is observed together with weak lines of the $^5D_4{\rightarrow}^7F_J$(J = 3, 4, and 6) transitions. A broad emission band peaking at 530 nm is observed at 10 K, while it disappears at room temperature. The decay times of $Tb^{3+}$ $^5D_4{\rightarrow}^7F_5$ emission are estimated to be 4.8 and 1.4 ms, respectively, at 10 and 295 K; those of the ${WO_4}^{2-}$ exciton emissions are 22 and 0.92 ${\mu}s$ at 10 and 200 K, respectively.

Study on the X-ray Spectra Dependence for Intensifying Screens (증감지의 X선 Spectra 의존성에 관한 연구)

  • 김영근;이경섭
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 1998.11a
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    • pp.93-96
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    • 1998
  • The X-ray spectra dependence for intensifying screens of medical radiography was investigated through analysis of the absorbed coefficiency(${\mu}$), absorbed efficiency(η$\sub$${\alpha}$/) and absorbed ratio(R). It was found that the absorbed coefficiency was increased in the order of CaWO$_4$$_4$ screen showed the highest value.

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Studies on Effective Utilization of X -ray Energy Using Intensifying Screens (증감지의 X-선 에너지 유효 이용에 관한 연구)

  • Kim, Y.K.;Lee, K.S.
    • Proceedings of the KIEE Conference
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    • 1998.11c
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    • pp.825-828
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    • 1998
  • The X-ray spectra dependence for intensifying screens of medical radiography was investigated through analysis of the absorbed coefficiency($\mu$), absorbed efficiency(${\eta}_{\alpha}$) and absorbed ratio(R). It was found that the absorbed coefficiency was increased in the order of $CaWO_4$$CaWO_4$ screen showed the highest value.

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Oxide and fluoride single crystals for scintillator applications

  • M. Nikl;K. Blazek;P. Fabeni;A. Vedda;M. Martini;M. Kobayashi;K. Shimamura;T. Fukuda
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.12 no.1
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    • pp.21-26
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    • 2002
  • Luminescence and scintillation properties of $PbWO_{4},\;XAIO_{3}$ (X = Y, Lu, Y-Lu) and $LiBaF_{3}$ based scintillators are reported. The effect of present and often not understood defect states is demonstrated in different scintillator parameters and related measurements are discussed. Importance of understanding of defect states participating in the processes of energy transfer and storage in the scintillating materials is emphasised.

Microwave Dielectric Properties of (Ba1-2xNa2x)(Mg0.5-xZrxW0.5)O3 Ceramics ((Ba1-2xNa2x)(Mg0.5-xZrxW0.5)O3 세라믹스의 마이크로파 유전특성)

  • Yoon, Sang-Ok;Hong, Chang-Bae;Lee, Yun-Joong;Kim, Shin
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.30 no.6
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    • pp.356-360
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    • 2017
  • We investigated the phase evolution, microstructure, and microwave dielectric properties of Na- and Zr-doped $Ba(Mg_{0.5}W_{0.5})O_3$ [i.e., ($Ba_{1-2x}Na_{2x})(Mg_{0.5-x}Zr_xW_{0.5})O_3$] ceramics. $BaWO_4$ as a secondary phase was observed in all compositions, and it increased as the dopant concentration increased. All specimens revealed a dense microstructure. For the composition of x=0.01, polyhedral grains were observed. As the dopant concentration increased, the densification and the grain growth were promoted by a liquid phase. The quality factor($Q{\times}f_0$) decreased remarkably, whereas the dielectric constant (${\varepsilon}_r$) tended to decrease as the dopant concentration increased. The dielectric constant, quality factor, and temperature coefficient of the resonant frequency of the composition of x=0.01 sintered at $1,700^{\circ}C$ for 1 h were 18.6, 216,275 GHz, and $-22.0ppm/^{\circ}C$, respectively.