• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.4
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• pp.131-135
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• 2020

Single crystal phased CaZrO₃ : Eu³⁺ phosphor have been synthesized by skull melting method. The crystal structure, morphology and optical properties of synthesized phosphor were investigated XRD (X-ray diffraction), SEM (scanning electron microscopy), UV (ultraviolet) fluorescence reaction and PL (photo luminescence). The starting materials having chemical composition of CaO: ZrO₂ : Eu₂O₃= 0.962 : 1.013 : 0.025 mol% were charged into a cold crucible. The cold crucible was 120 mm in inner diameter and 150 mm in inner height, and 3 kg of mixed powder (CaO, ZrO₂ and Eu₂O₃) was completely melted within 1 hour at an oscillation frequency of 3.4 MHz, maintained in the molten state for 2 hours, and finally air-cooled. The XRD results show that synthesized phosphor is stabilized in orthorhombic perovskite structure without any impurity phases. The synthesized phosphor could be excited by UV light (254 or 365 nm) and the emission spectra results indicated that bright red luminescence of CaZrO₃ : Eu³⁺ due to magnetic dipole transition ⁵D₀→⁷F₂ at 615 nm was dominant.

• Journal of Astronomy and Space Sciences
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• v.22 no.3
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• pp.187-196
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• 2005

From the line ratios of Si III] 1892 to C III] 1909 (Feibelman & Aller 1987), we estimated the BLR electron densities and their changes of Seyfert 1 galaxy NGC 7469 using IUE spectra observed from June 11 to July 29, 1996 (Wanders et al. 1997). We separated blended Si III] and C III] lines using the STARLINK/DIPSO and measured their fluxes within the error of $12.4\%\;and\;6.6\%,$ respectively. Electron density fluctuated from $10^{9.69}\;to\;10^{10.93}$ during about two month period, i.e. 17.3 times density variation within 50 days. We also derived time delays from UV emission line variations .elative to the continuum $(at\;1315{\AA}):$ 2 days for C IV, 4 days for C III], 8 days for Si III]. This suggests that their stratified UV line emission regions are at 0.002 pc, 0.004 pc and 0.006 pc, respectively, from the central region. Based on the BLR sizes and their rotation velocities deduced from the line profiles, we estimate the central black hole mass as about $10^6M_{\odot}$

• Journal of the Korean Ceramic Society
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• v.42 no.3 s.274
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• pp.145-149
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• 2005

[ $Eu^{2+}$ ]-activated barium magnesium silicate phosphor, $(Ba,Ca)_{3}MgSi_{2}O_{8}:Eu_{x}$, has been known to emit blue-green light. In this study we report the manufacturing processes for producing either pure green or pure blue light-emitting phosphor from the same composition of $Ba_{2-x}Ca_{2}CaMgSi_{2}O_{8}:Eu_{x}$ (0 < x < 1) by controlling heat treatment conditions. Green light emitting phosphor of $Ba_{1.9}CaMgSi_{2}O_{8}:Eu_{0.1}$ can be produced under the sample preparation condition of highly reducing atmosphere of $23\%\;H_2/77\%\;N_2$, while blue or blue-green light emitting phosphor under reducing atmosphere of $5\~20\%\;H_2\;/\;95\~80\%$ N_2. The green light-emitting phosphors are prepared in two steps: firing at $800\~1000^{\circ}C$ for $2\~5$ h in air then at $1100\~1350^{\circ}C$ for 2-5 h under reducing atmo­sphere $23\%$ $H_2/77\%\;N_2$. The excitation spectrum of the green light-emitting phosphor shows a broadband of $300\~410$ nm. The emission spectrum has a maximum intensity at the wavelength of about 501 nm. The CIE value of green light emission is (0.162, 0.528). The pure blue light-emitting phosphors can be produced using the $Ba{2_x}CaMgSi_{2}O_{8}:Eu_{x}$ by introducing additional firing step at $1150\~1300^{\circ}C$ in air before the final reducing treatment. The XRD analysis shows that the green light-emitting phosphor mainly consisted of $Ba_{1.31}Ca_{0.69}SiO_{4}$ (JCPDS $\#$ 36-1449) and other minor phases i.e., $MgSiO_3$ (JCPDS $\#$ 22-0714) and $Ca_{2}BaMgSi_{2}O_{8}$ (JCPDS $\#$ 31-0128). The blue light-emitting phosphor mainly consisted of $Ca_{2}BaMgSi_{2}O_{8}$ phase.

• Korean Chemical Engineering Research
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• v.44 no.6
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• pp.609-613
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• 2006

Ba2-xSrxSiO4:Eu2+ phosphor particles with the high photoluminescence (PL) intensity under long wavelength ultraviolet (UV) were prepared by spray pyrolysis. The photoluminescence, morphological and crystalline characteristics of $Ba_{2-x.}Sr_{x.}SiO_4:Eu^{2+}$ phosphor particles prepared by spray pyrolysis were investigated. $Ba_{2-x.}Sr_{x.}SiO_4:Eu^{2+}$ phosphor particles prepared by spray pyrolysis had various colors from bluish green to yellow by changing the ratio of barium and strontium of the host material. In case of x=0, the main emission peak of $Ba_2SiO_4:Eu^{2+}$ phosphor was 500 nm. In case of x=2, the main emission peak of $Sr_2SiO_4:Eu^{2+}$ phosphor was 554nm. $Ba_{2-x.}Sr_{x.}SiO_4:Eu^{2+}$ phosphor particles obtained by spray pyrolysis had spherical shape and hollow structure. On the other hand, the post-treated $Ba_{2-x.}Sr_{x.}SiO_4:Eu^{2+}$ phosphor particles had large size and irregular shape. The $Ba_{1.488}Sr_{0.5}SiO_4:Eu_{0.012}{^{2+}}$ phosphor particles had the maximum PL intensity after post-treatment at temperature of $1300^{\circ}C$ for 3h under reduction atmosphere.

• Clean Technology
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• v.15 no.2
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• pp.81-90
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• 2009

In this study various cleaning evaluation methods were tested and comparatively evaluated to help cleaning industry. In order to select alternative cleaning agents objectively and systematically, various cleaning evaluation methods such as gravimetric, optically simulated electron emission (OSEE), contact angle, and analytical instrument methods were employed for cleaning contaminants such as flux, solder and grease. The analytical instruments used in this work were Fourier transform infrared spectroscopy (FTIR), ultraviolet visible spectroscopy (UV-VIS) and high performance liquid chromatography (HPLC). The gravimetric method was able to measure cleaning efficiencies easily and simply, but it was not easy to analyze them precisely because of its limitation in the gravimetric measurement. However, the OSEE technique was able to measure quickly and precisely the clean ability of cleaning agents in comparison with the gravimetric method. The contact angle method was found to be necessary for taking special precaution in its application to the cleaning evaluation due to possible formation of tiny organic film on the substrate surface which might be generated from contaminants and cleaning agents. In case of precision analysis that cannot be done by gravimetric method, fine analytical instruments such as UV-VIS, FTIR and HPLC could be used in analyzing trace amount of flux, solder and grease quantitatively, which were extracted from the surface by special solvents.

• Atmosphere
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• v.21 no.4
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• pp.429-438
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• 2011

The climatology of surface UV radiation for Seoul, presented in Cho et al. (1998; 2001), has been updated using measurement of surface erythemal ultraviolet (EUV) and total ultraviolet (TUV) irradiance (wavelength 286.5~363.0 nm) by a Brewer Spectrophotometer (MK-IV) for the period 2004~2010. The analysis was also carried out together with the broadband total (global) solar irradiance (TR ; 305~2800 nm) and cloud amount to compare with the UV variations, measured by Seoul meteorological station of Korean Meteorological Agency located near the present study site. Under all-sky conditions, the day-to-day variability of EUV exhibits annual mean of 98% in increase and 31% in decrease. It has been also shown that the EUV variability is 17 times as high as the total ozone in positive change, whereas this is 6 times higher in negative change. Thus, the day to day variability is dominantly caused rather by the daily synoptic situations than by the ozone variability. Annual mean value of daily EUV and TUV shows $1.62kJm^{-2}$ and $0.63MJm^{-2}$ respectively, whereas mean value of TR is $12.4MJm^{-2}$ ($143.1Wm^{-2}$). The yearly maximum in noon-time UV Index (UVI) varies between 9 and 11 depending on time of year. The highest UVI shows 11 on 20 July, 2008 during the period 2004~2010, but for the period 1994~2000, the index of 12 was recorded on 13 July, 1994 (Cho et al., 2001). A 40% of daily maximum UVI belongs to "low (UVI < 2)", whereas the UVI less than 5% of the maximum show "very high (8 < UVI < 10)". On average, the maximum UVI exceeded 8 on 9 days per year. The values of Tropospheric Emission Monitoring Internet Service (TEMIS) EUV and UVI under cloud-free conditions are 1.8 times and 1.5 times, respectively, higher than the all-sky measurements by the Brewer. The trend analysis in fractional deviation of monthly UV from the reference value shows a decrease of -0.83% and -0.90% $decade^{-1}$ in the EUV and TUV, respectively, whereas the TR trend is near zero (+0.11% $decade^{-1}$). The trend is statistically significant except for TR trend (p = 0.279). It is possible that the recent UV decrease is mainly associated with increase in total ozone, but the trend in TR can be attributed to the other parameters such as clouds except the ozone. Certainly, the cloud effects suggest that the reason for the differences between UV and TR trends can be explained. In order to estimate cloud effects, the EUV, TUV and TR irradiances have been also evaluated for clear skies (cloud cover < 25%) and cloudy skies (cloud cover ${\geq}$ 75%). Annual mean values show that EUV, TUV and TR are $2.15kJm^{-2}$, $0.83MJm^{-2}$, and $17.9MJm^{-2}$ for clear skies, and $1.24kJm^{-2}$, $0.46MJm^{-2}$, and $7.2MJm^{-2}$ for cloudy skies, respectively. As results, the transmission of radiation through clouds under cloudy-sky conditions is observed to be 58%, 55% and 40% for EUV, TUV and TR, respectively. Consequently, it is clear that the cloud effects on EUV and TUV are 18% and 15%, respectively lower than the effects on TR under cloudy-sky conditions. Clouds under all-sky conditions (average of cloud cover is 5 tenths) reduced the EUV and TUV to about 25% of the clear-sky (cloud cover < 25%) values, whereas for TR, this was 31%. As a result, it is noted that the UV radiation is attenuated less than TR by clouds under all weather conditions.

• Journal of the Korean Ceramic Society
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• v.56 no.2
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• pp.178-183
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• 2019

A process of fabricating the foamed glass that has closed pores with 8 ~ 580 ㎛ sizes without a blowing agent by sintering 10 ㎛ boron-free glass powder composed of CaO, MgO, SO₃, Al₂O₃-83 wt% SiO₂ at a molding pressure of 0 ~ 120 MPa and a sintering temperature of 750 ~ 1000℃ was investigated. To analyze the glass transition temperature of glass powder, thermogravimetric analysis-differential thermal analysis (TGA-DTA) method were used. The microstructure and pore size of foamed glass were examined using the optical microscopy and field emission scanning electron microscopy (FE-SEM). For the thermal diffusivity and color of the fabricated samples, a heat flow meter and ultraviolet-visible-near-infrared (UV-VIS-NIR)-colormetry were used, respectively. In the TGA-DTA result, the glass transition temperature of glass powder was confirmed to be 626℃. In the microstructure result, closed pores of 7 ~ 20 ㎛ were formed at 750 ~ 900℃, and they were not affected by the molding pressure and sintering temperature. However, at 1,000℃, when there was 0 MPa molding pressure, closed pores of 580 ㎛ were confirmed, and the pore size decreased as the molding pressure increased. Moreover, at a molding pressure of 30 MPa or higher, closed pores of approximately 400 ㎛ were formed. The porosity showed an increasing trend of smaller molding pressure and larger sintering temperature, and it was controllable in the range of 5.69 ~ 68.45%. In the thermal diffusivity result, there was no change according to the molding pressure, and, by increasing the sintering temperature, up to 0.115 W/m·K could be obtained. The Lab color index (CIE-Lab) results all showed a similar translucent white color regardless of molding pressure and sintering temperature. Therefore, based on the foamed glass without boron and blowing agent, it was confirmed that white foamed glass, which has closed pores of 8 ~ 580 ㎛ and a thermal diffusivity characteristic of 0.115 W/m·K, can be fabricated by changing the molding pressure and sintering temperature.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.6
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• pp.658-663
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• 2018

Current measuring methods for air quality are based on ground measurement networks and satellite data. New methods of collecting evidence with advanced sensors are needed because current methods have limitations in collecting evidence for the illegal emission of air pollutants at narrow areas or specific sites. This study analyzed the possibility of using an ultraviolet hyperspectral sensor to measure the concentration of nitrogen dioxide and sulfur dioxide. Two types of spectra were used: simulated spectra for gases with various concentrations using a radiative transfer model and observed spectra for each gas for a concentration. To understand the possibility of using a hyperspectral sensor, the differences between the simulated spectra and the observed spectra were analyzed, and the variation of simulated spectra were then analyzed according to the concentration. The results showed good agreement between observed spectra and simulated spectra. In addition, the absorption depth at specific wavelengths in the simulated spectra had a very strong correlation with the gas concentration. The gas concentration could be estimated using the hyperspectral sensor. In the future, validation would be needed to estimate the gas concentration through observations of various concentrations of gases using a hyperspectral sensor.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.293-293
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• 2014

Over last decade InGaN alloy structures have become the one of the most promising materials among the numerous compound semiconductors for high efficiency light sources because of their direct band-gap and a wide spectral region (ultraviolet to infrared). The primary cause for the high quantum efficiency of the InGaN alloy in spite of high threading dislocation density caused by lattice misfit between GaN and sapphire substrate and severe built-in electric field of a few MV/cm due to the spontaneous and piezoelectric polarizations is generally known as the strong exciton localization trapped by lattice-parameter-scale In-N clusters in the random InGaN alloy. Nonetheless, violet-emitting (390 nm) conventional low-In-content InGaN/GaN multi-quantum wells (MQWs) show the degradation in internal quantum efficiency compared to blue-emitting (450 nm) MQWs owing higher In-content due to the less localization of carrier and the smaller band offset. We expected that an improvement of internal quantum efficiency in the violet region can be achieved by replacing the conventional low-In-content InGaN/GaN MQWs with ultra-thin, high-In-content (UTHI) InGaN/GaN MQWs because of better localization of carriers and smaller quantum-confined Stark effect (QCSE). We successfully obtain the UTHI InGaN/GaN MQWs grown via employing the GI technique by using the metal-organic chemical vapor deposition. In this work, 1 the optical and structural properties of the violet-light-emitting UTHI InGaN/GaN MQWs grown by employing the GI technique in comparison with conventional low-In-content InGaN/GaN MQWs were investigated. Stronger localization of carriers and smaller QCSE were observed in UTHI MQWs as a result of enlarged potential fluctuation and thinner QW thickness compared to those in conventional low-In-content MQWs. We hope that these strong carrier localization and reduced QCSE can turn the UTHI InGaN/GaN MQWs into an attractive candidate for high efficient violet emitter. Detailed structural and optical characteristics of UTHI InGaN/GaN MQWs compared to the conventional InGaN/GaN MQWs will be given.

• Analytical Science and Technology
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• v.25 no.3
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• pp.197-206
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• 2012

Ambers are composed of polymer molecules which contain aromatic moieties such as benzene, naphthalene, phenanthrene and anthracene. They emit fluorescence when irradiated with ultraviolet light, which was used for confirming an amber. The fluorescence of amber, however, tends to decrease as the surface of amber is weathered with light, heat, oxygen for a long time. In this study, the reliability of confirming amber with its fluorescence by measuring the changes of fluorescence after artificial aging. Aging factors were UV light (${\lambda}$=340 nm), oxygen with heat (100%, $90^{\circ}C$) and heat ($90^{\circ}C$) and aging time was for 5, 15, 30 and 60 days, respectively. In the excitation and emission spectra of amber, the intensity decreased and the maximal wavelength was shifted to longer wavelength with artificial aging time. Especially, there was a drastic decrease in the intensity of spectra to 1.7% of initial value after 60 days aging under oxygen with heat. Only in Colombian amber there showed an increase of fluorescence intensity for a certain aging time, which could be explained by the production of aromatic ring in the presence of light and heat. Conclusively, the fluorescence can be lessened by the natural weathering with light, heat and oxygen and it is not accurate to recognize amber just with UV irradiation method.