• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.156-156
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• 2011

Nanocrystalline $Ca_2Gd_8Si_6O_{26}$ (CGS) : $Sm^{3+}$ and CGS : $Tb^{3+}/Sm^{3+}$ phosphors were prepared by solvothermal reaction method for light emitting diode (LED) and field emission display (FED) applications. The XRD patterns of these phosphors confirmed their oxyapatite structure in the hexagonal lattice. The visible luminescence properties of these phosphors were investigated by exciting with ultraviolet (UV) or near-UV light and low voltage electron beam. The photoluminescence (PL) properties of $Ca_2Gd_8Si_6O_{26}$ (CGS) : $Sm^{3+}$ and CGS : $Tb^{3+}/Sm^{3+}$ phosphors were investigated as a function of $Sm^{3+}$ concentration. Cathodoluminescence (CL) properties were examined by changing the acceleration voltage. The CGS : $Sm^{3+}$ showed the dominant orange emission due to the $^4G_{5/2}{\rightarrow}^6H_{7/2}$ transition. The CGS : $Tb^{3+}/Sm^{3+}$ phosphor showed the green, white and orange emissions when excited with 275, 378, and 405 nm wavelengths, respectively. The chromaticity coordinates of these phosphors were comparable to or better than those of standard phosphors for LED or FED devices.

• Journal of The Korean Astronomical Society
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• v.39 no.3
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• pp.73-80
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• 2006

We analyze the extinction law towards several B1V stars-members of our Galaxy, searching for possible discrepancies from the galactic average extinction curve. Our photometric data allow to build extinction curves in a very broad range: from extreme UV till infrared. Two-colour diagrams, based on the collected photometric data from the ANS UV satellite, published UBV measurements and on the infrared 2MASS data of the selected stars, are constructed. Slopes of the fitted straight lines are used to build the average extinction curve and to search for discrepant objects. The selected stars have also been observed spectroscopically from the Terskol and ESO Observatories; these spectra allow to check their Sp/L's. The spectra of only about 30% of the initially selected objects resemble closely that of HD144470, considered as the standard of B1 V type. Other spectra either show some emission features or belong clearly to another spectral types. They are not used to build the extinction curve. Two-colour diagrams, constructed for the selected B1 V stars, showing no emission stellar features, prove that the interstellar extinction law is homogeneous in the Galaxy. Both the shape of the curve and the total-to-selective extinction ratio do not differ from the galactic average and the canonical value(3.1) respectively. The circumstellar emissions usually cause some discrepancies from the average interstellar extinction law; the discrepancies observed in the extraterrestrial ultraviolet, usually follow some misclassifications.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.535-537
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• 2015

Interpreting ultraviolet-to-infrared (UV-to-IR) observations of galaxies in terms of constraints on physical parameters-such as stellar mass ($M_{\ast}$) and star formation rate (SFR)-requires spectral synthesis modelling. We investigate how increasing the level of sophistication of the standard simplifying assumptions of such models can improve estimates of galaxy physical parameters. To achieve this, we compile a sample of 1048 galaxies at redshifts 0.7 < z < 2.8 with accurate photometry at rest-frame UV to near-IR wavelengths from the 3D-HST Survey. We compare the spectral energy distributions of these galaxies with those from different model spectral libraries to derive estimates of the physical parameters. We find that spectral libraries including sophisticated descriptions of galaxy star formation histories (SFHs) and prescriptions for attenuation by dust and nebular emission provide a much better representation of the observations than 'classical' spectral libraries, in which galaxy SFHs are assumed to be exponentially declining functions of time, associated with a simple prescription for dust attenuation free of nebular emission. As a result, for the galaxies in our sample, $M_{\ast}$ derived using classical spectral libraries tends to be systematically overestimated and SFRs systematically underestimated relative to the values derived adopting a more realistic spectral library. We conclude that the sophisticated approach considered here is required to reliably interpret fundamental diagnostics of galaxy evolution.

• Journal of the Korean Ceramic Society
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• v.40 no.3
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• pp.262-267
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• 2003

The heteroepitaxial ZnO thin film on sapphire (0001) substrate was prepared by an off-axis Radio Frequency(RF) magnetron sputtering. The crystallinity of ZnO thin film was affected by deposition pressure, RF power, and substrate temperature. High quality heteroepitaxial ZnO thin film was obtained when the kinetic energy of sputtered particles is well harmonized with the surface mobility. In the result of Photoluminescence(PL) of heteroepitaxial ZnO thin film, Ultraviolet(UV) emissions at 3.36 and 3.28 eV were observed at low(17 K) and Room Temperature(RT). respectively. As the ZnO thin film was annealed in O$_2$ambient, the crystallinity was improved while UV emission was drastically decreased.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.473-474
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• 2005

Blue-emitting polymers containing carbazole units In main chains were synthesized by palladium catalyzed polycondensation of aniline with dibromo-substituted monomers such as 3,6-dibromocarbazole, N-(2-ethylhexyl)-3,6-dibromocarbazole, and bis[6-bromo-N-(2-ethylhexyl)-carbazole-3-yl], respectively. All synthesized polymers exhibited relatively good solubility in common organic solvents, considerable molecular weights and high resistance to thermal degradation. From UV-Vis absorption and photoluminescence (PL) spectra of these solution-processable polymers, $\lambda_{max,UV}$ were in the range of 290 ~ 340 nm and $\lambda_{max,PL}$ were in the blue emission range of 440 ~ 478 nm, The polymers had HOMO energy (-5.19 ~ -5.64 eV) and wide band gap energy (2,91 - 3.42 eV).

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.565-568
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• 2008

In this study, a blue-emitting $Sr_2MgSi_2O_7:Eu^{2+}$ (SMS) phosphor for white light-emitting diodes is reported. Through transition of $4f{\rightarrow}5d$ in $Eu^{2+}$, SMS showed a strong blue emission under UV excitation. Additionally, the variation of emission wavelength of SMS is explained by crystal field effect and is supported by rietveld refinement.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1090-1092
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• 2006

There is provided white light illumination system including a radiation source, a first luminescent material having a peak emission wavelength of about 575 to about 620 nm, a second luminescent material having a peak emission wavelength of about 495 to about 550 nm, which is different from the first luminescent material and a third luminescent material having a peak emission wavelength of about 420 to about 480 nm, which is different from the first and second luminescent materials. The LED may be a UV LED and the luminescent materials may be a blend of three phosphors. A human observer perceives the combination of the blue, green and red phosphor emissions as white light.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.968-971
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• 2003

Due to a low efficiency of phosphor with large Stoke shift in Vacuum Ultra Violet (VUV) excitation environment, new PDP phosphors which can be excited in UV excitation environment need to be developed. In this study, $Zn_2SiO_4:Tb$ phosphor was synthesized by solid-state reaction method at $1300^{\circ}C$ with varying Tb concentration, and its cross relaxation effect was observed by Photoluminescence (PL) measurement. In order to decrease $^5D_3{\to}7F_j$ transition with blue emission in $Zn_2SiO_4:Tb$ phosphor, Dy, co-activator element, was added to $Zn_2SiO_4:Tb$ phosphor. In 254nm excitation environment, broad-emission peak was observed around 524nm, green emission.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.69.2-69.2
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• 2010

The far-ultraviolet (FUV) H2 and C IV emission images and spectra of Orion Eridanus Superbubble (OES) is hereby presented. The OES seems to consists of multiple phase through the detection of highly-ionized gas and pervasive neutral hydrogen. The former is traced by hot gas while the latter is traced by cold medium. A spectral image made with H2 fluorescent emission shows that the spatial distribution of hydrogen molecule is well correlated with the dust map. The model spectra was taken from a photodissociation region (PDR) radiation code which find a best suitable parameter such as hydrogen density, gas temperature and incident uv intensity of the radiation field. C IV emission is caused by intermediate temperature ISM about 10^4.5 K~10^6 K. Therefore we could get more clear evidence to reveal the structure of OES. Feature of spectra for the each sub region is also presented and discussed. The data were obtained with the Far-Ultraviolet Imaging Spectrograph (FIMS) and the whole data handling were followed by previous FIMS analysis.

• Analytical Science and Technology
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• v.11 no.3
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• pp.194-201
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• 1998

The formaldehyde vapor produced from wood and steel furniture was absorbed in distilled water and derivatized with acetylacetone and determined by UV-visible spectrophotometry. Variation in HCHO emission with time was monitored at room temperature. The emission of volatile compounds from wood, wood-based and steel-based materials was investigated in a 50 mL glass vial. The concentration of the gases emitted in a glass vial was determined by ion-trap GC-MS.