• Macromolecular Research
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• v.17 no.9
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• pp.672-681
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• 2009

A series of inert and photo-stable Er(III)-encapsulated complexes based on ${\pi}$-extended dendritic anthracene ligands bearing G3-aryl-ether dendron ([G3-AnX]-$CO_2H$), which retain different ${\pi}$-bridging systems, such as single (X= S), double (X= D) and triple (X= T) bonds was designed and synthesized to establish the structure-property relationship. The near infrared emission intensities of Er(III)-encapsulated complexes were enhanced dramatically by increasing the ${\pi}$-conjugated extension of anthracene ligands. The time-resolved luminescence spectra show monoexponential decays with a lifetime of $2.0{\sim}2.4ms$ for $Er^{3+}$ ions in thin films, and calculated intrinsic quantum yields of $Er^{3+}$ ions are in the range of $0.025{\sim}0.03%$. As a result, all Er(III)-encapsulated dendrimer complexes exhibit the near IR emission with the following order: $Er^{3+}-[G3-AnD]_3$(terpy) > $Er^{3+}-[G3-AnS]_3$(terpy) ${\approx}$ $Er^{3+}-[G3-AnT]_3$(terpy), because $Er^{3+}-[G3-AnD]_3$(terpy) has a higher relatively spectral overlap J value and energy transfer efficiency. In addition, the lack of detectable phosphorescence and no significant spectral dependence of the ${\pi}$-extended anthracene moieties on the solvent polarity support energy transfer from their singlet state to the central $Er^{3+}$ ion taking place in $Er^{3+}-[G3-AnX]_3$(terpy).

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.44.2-44.2
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• 2015

Radiative transfer programs have been developed to simulate near-IR spectra of Titan. The formalism of the radiative transfer calculations includes the absorption and emission lines of $CH_4$, $C_2H_2$, $C_2H_6$, and HCN, and continua produced by Titanian haze particles. Absorption and scattering of sunlight by haze particles are considered by employing a two-stream approximation and a spherical-shell model for the atmospheric layers of Titan. Various constraints on the radiative transfer calculations for generating synthetic spectra will be discussed and presented. Several examples of comparisons between the synthetic spectra and recent spectral observations of Titan will also be presented.

• Journal of the Korean earth science society
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• v.26 no.2
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• pp.149-159
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• 2005

Simultaneous observations of MODIS (Moderate-resolution Imaging Spectroradiometer) onboard the Aqua and Terra satellites and weather station at ground near the Inchon International Airport (37.2-37.7 N, 125.7-127.2 E) during the period from December 2002 to September 2004 have been utilized in order to analyze the characteristics of satellite-observed infrared (IR) and visible data under fog and clear-sky conditions, respectively. The differences $(T_{3.7-11})$ in brightness temperature between $3.75{\mu}m\;and\;11.0{\mu}m$ were used as threshold values for remote-sensing fog (or low clouds) from satellite during day and night. The $T_{3.7-11}$ value during daytime was greater by about 21 K when it was foggy than that when it was clear, but during nighttime fog it was less by 1.5 K than during nighttime clear-sky. The value was changed due to different values of emission of fog particles at the wavelength. Since the near-IR channel at $3.7{\mu}m$ was affected by solar and IR radiations in the daytime, both IR and visible channels (or reflectance) have been used to detect fog. The reflectance during fog was higher by 0.05-0.6 than that during clear-sky, and varied seasonally. In this study, the threshold values included uncertainties when clouds existed above a layer of fog.

• Bulletin of the Korean Chemical Society
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• v.28 no.8
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• pp.1256-1260
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• 2007

Two β-diketone derivatives bearing triphenylene (1-naphthalene-2-yl-3-triphenylen-2-yl-propane-1,3-dione (NTPD)) and naphthalene (1,3-di-naphthalene-2-yl-propane-1,3-dione (DNPD)) and their Ln(III) complexes (Ln = Er or Gd) were synthesized and their photophysical properties were investigated. The sensitized emission of Er3+ ion in Er3+-[NTPD]3(terpy) and Er3+-[DNPD]3(terpy) was observed upon excitation at absorption maximum of ligands. Their photophysical studies indicate the sensitization of Er3+ luminescence by energy transfer through the excited triplet state of β-diketone ligand. The energy transfer rate through the excited triplet state of β-diketone ligand to Er3+ ion occurs faster than that of the oxygen quenching rate.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.52.1-52.1
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• 2010

The Japanese infrared (IR) space mission AKARI monitored the brightness in the fields very close to the north ecliptic pole (NEP) with nine wavebands in Infrared Camera (IRC), which cover the wavelength range from 2 to $24{\mu}m$. We reduced the NEP monitor observations and examined the smoothness of the sky background brightness. Our analysis shows that the background brightness is smooth over a frame of about $10'\times10'$ within about 0.1% deviation in mid-IR. Because the zodiacal light (ZL) and emission (ZE) dominate the diffuse sky brightness in the near- and mid-IR wavelengths, the background brightness varies with season through a year. We tried sinusoidal fittings to the observed NEP background brightness. The fitting analysis shows that the sine function is successful in describing the seasonal variation of the ZL and ZE within 2% deviations from the observed brightness, especially for the 15, 18, and $24{\mu}m$ bands, within 0.3%. These results will provide limits and caveats for the studies of the cosmic infrared background radiation.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.68.1-68.1
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• 2019

Using IPHAS $H{\alpha}$ data, we found bright $H{\alpha}$ regions inside the elongated $^{13}CO$ cavity around a Herbig star, MWC 1080. To investigate the ionized hydrogen regions and the molecular cavity, we perform near-IR high-resolution spectroscopic of hydrogen Brackett lines and molecular hydrogen lines by Immersion GRating INfrared Spectrograph (IGRINS) observations. We detected broad Brackett line series and sharp molecular lines with various velocity components. We present three ionized hydrogen regions (near MWC 1080A, MWC 1080E, and CO boundary) with different line widths, central radial velocities, and line ratios. We also show two spatially-separate $Br{\gamma}$ ${\lambda}2.1662{\mu}m$ peaks near MWC 1080A. To reveal a 3D structure of the cavity around MWC 1080, we try to use the detected sharp molecular lines.

• 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.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.207-207
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• 2013

기존의 그래핀 성장에 관한 연구는 열화학기상증착법(Chemical vapor deposition; CVD)을 이용한다. 그래핀 성장 제어 요소로는 촉매 기판인 전이 금속[Ru, Ir, Co, Re, Pt, Pd, Ni, Cu], 기판 전처리 과정, 수소/메탄 가스 혼합비, 작업 진공 상태, 기판온도[$800{\sim}1,000^{\circ}C$, 냉각 속도 등으로 보고 되고 있다. 그래핀 성장 원리는 Cu 촉매 기판에 메탄 가스를 $1,000^{\circ}C$ 온도에서 분해해서 탄소를 고용 시킨 후 급랭하는 도중에 석출되는 탄소에 의해 그래핀 시트가 형성되는 것으로 알려져 있다. 기존의 CVD를 열원을 이용할 경우 내부 챔버에 생기는 잠열에 의해 cooling profile의 제어가 용이하지 않다. 본 연구에서는 근적외선(Near Infrared; NIR) 열원을 이용한 CVD로 챔버 내부 잠열을 최소화하고, 냉각 공정을 Natural, Linear, Convex cooling type으로 디자인해서 cooling profile 제어가 그래핀 성장에 미치는 영향을 연구 하였다. 이렇게 성장된 그래핀을 임의의 기판(SiO2, Glass, PET film) 위에 습식방법으로 전이 시킨 후, 전기적 구조적 및 광학적 특성을 면저항(four-point probe), 전계방사 주사전자현미경(Field Emission Scanning Electron Microscope; FE-SEM), 마이크로 라만 분광법(Micro Raman spectroscopy) 및 광학현미경(optical microscope), 투과도(UV/Vis spectrometer)의 측정으로 잠열이 최소화된 NIR-CVD에서 cooling profile에 따른 그래핀 성장을 평가하였다.

• Korean Journal of Materials Research
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• v.28 no.2
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• pp.124-128
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• 2018

N-type porous silicon (PS) layers and thermally oxidized PS layers have been characterized by various measuring techniques such as photoluminescence (PL), Raman spectroscopy, IR, HRSEM and transmittance measurements. The top surface of PS layer shows a stronger photoluminescence peak than its bottom part, and this is ascribed to the difference in number of fine silicon particles of 2~3 nm in diameter. Observed characteristics of PL spectra are explained in terms of microstructures in the n-type PS layers. Common features for both p-type and n-type PS layers are as follows: the parts which can emit visible photoluminescence are not amorphous, but crystalline, and such parts are composed of nanocrystallites of several nm's whose orientations are slightly different from Si substrate, and such fine silicon particles absorb much hydrogen atoms near the surfaces. Light emission is strongly dependent on such fine silicon particles. Photoluminescence is due to charge carrier confinement in such three dimensional structure (sponge-like structure). Characteristics of visible light emission from n-type PS can be explained in terms of modification of band structure accompanied by bandgap widening and localized levels in bandstructure. It is also shown that hydrogen and oxygen atoms existing on residual silicon parts play an important role on emission stability.

• Current Optics and Photonics
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• v.3 no.3
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• pp.248-255
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• 2019

Spherical $CeO_2:Ho^{3+}/Yb^{3+}$ particles were synthesized using spray pyrolysis, and the upconversion (UC) properties were investigated with changing the preparation conditions and the infrared pumping power. The resulting particles had a size of about $1{\mu}m$ and hollow structure. The prepared $CeO_2:Ho^{3+}/Yb^{3+}$ particles exhibited intense green emission due to the $^5F_4/^5S_2{\rightarrow}^5I_8$ transition of $Ho^{3+}$ and showed weak red or near-IR peaks. In terms of achieving the highest UC emission, the optimal concentrations of $Ho^{3+}$ and $Yb^{3+}$ were 0.3% and 2.0%, respectively. The UC emission intensity of prepared $CeO_2:Ho^{3+}/Yb^{3+}$ particles had a linear relationship with crystallite size and concentration quenching was caused by dipole-dipole interaction between the same ions. Based on the dependency of UC emission on the pumping power, the observed green upconversion was achieved through a typical two-photon process and concluded that the main energy transfer from $Yb^{3+}$ to $Ho^{3+}$ was involved in the ground-state adsorption (GSA) process.