• Korean Journal of Materials Research
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• v.15 no.8
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• pp.508-513
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• 2005

[ $TiO_2-Fe_2O_3$ ] nanocomposite powders for magnetic photocatalyst were synthesized by sol-gel process, in which $TiO_2$ photocatalytic layer was formed on the surface of $\gamma-Fe_2O_3$ magnetic core. Transmission electron microscopy (TEM) observation and X-ray diffractometry (XRD) analysis revealed that$\gamma-Fe_2O_3$ nanoparticles, $10\~20nm$ in diameter, were coated by $TiO_2$ shell of 5nm in thickness and $TiO_2$ was anatase phase. Also hydroxyl group (-OH) used to decompose organic compounds was detected by Fourier transformation infrared spectrometry(FT-IR) analysis. UV-Visible spectrophotometry results showed that light absorption occurred in the wavelength range of $400\~700 nm$, and the band gap energy $(E_g)$ of powder was 1.8 eV. Finally it was found that the coercivity $(H({ci})$ and saturation magnetization $(M_s)$ of the powder were 79 Oe and 14.8 emu/g, respectively as experimental vibrating sample magnetometer (VSM) measurements.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.347-348
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• 2013

To obtain high conversion efficiency in InGaN-based solar cells, it is critical to grow high indium (In) composed InGaN layer for increasing sun light absorption wavelength rage. At present, most InGaN-based solar cells adopt InGaN/GaN multi-quantum-well (MQW) structure for high crystalline quality of InGaN with high In composition. In this study, we fabricated and compared the performances of two types of InGaN/GaN MQW solar cells which have the 15% (SC 15) and 25% (SC 25) of In composition at quantum well layer. Although both devices showed similar dark current density and leakage current, SC 15 showed better performance under AM 1.5G illumination as shown in Fig. 1. It is interesting to note that SC 25 showed severe current density decrease as increasing voltages. As a result, it lowered short circuit current density and fill factor of the device. However, SC 15 showed steady current density and over 75 % of fill factor. To investigate these differencesmore clearly, we analyzed their photoluminescence (PL) spectra under various applied voltages as shown in Fig. 2. At the same time, photocurrent, which was generated by PL excitation, was also measured as shown in Fig. 3. Further, we investigated the relationship between piezoelectric field and performance of InGaN based solar cell varying indium composition.

• Journal of the Korean Applied Science and Technology
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• v.33 no.1
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• pp.136-142
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• 2016

The influences of fluorescence, scattering, and flocculation in random media were interpreted for the scattered fluorescence intensity and wavelength, it has been studied the molecular properties by the spectroscopy of laser induced fluorescence(LIF). The effects of optical properties in scattering media have been found by the optical parameters(${\mu}_s$, ${\mu}_a$, ${\mu}_t$). Flocculation is an important step in many solid-liquid separation processes and is widely used in Photodynamic therapy. The interactions of several colloid particles can come into play which have major effect on the flocculation and LIF process. We measured scattering and fluorescence spectra of the sample in vitro as function of distance from lase source to detector. The value of scattering coefficient ${\mu}_s$ is and ${\beta}$-carotene were measured as larger values(I, ${\delta}$) by means of closer distance from source to detector.

• Journal of the Microelectronics and Packaging Society
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• v.20 no.3
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• pp.19-22
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• 2013

Recently, high speed transmission and large information demand have been increased. Also, researches of integrated optical device for large production and high-efficient planar lightwave circuit (PLC) have been increased. In this paper, integrated optical alignment is proposed which makes passive alignment between optical device and optical fiber possible. The integrated optical device consists of splitter structures which have one input and two outputs. The proposed integrated structure was fabricated by roll-to-roll (RTR) processing method. This method enables to manufacture continuously and the processing time can be shortened. Optical property of the fabricated optical device showed 3.9 dB insertion loss and 0.2 dB optical uniformity using the light source with 1550 nm wavelength.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.49.2-49.2
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• 2014

The MIRIS (Multi-purpose InfraRed Imaging System) is a compact IR space Telescope, which has been developed by KASI since 2008 as the main payload of Korean STSAT-3. It was launched successfully by a Dnepr Rocket at Yasny Launch site, Russia in November 2013. After the launch, the STSAT-3 successfully settled down at Sun synchronous orbit with altitude of ~ 600km. Communications were regularly made between the ground station and the MIRIS with other secondary payload. We made a series of tests of the MIRIS during the verification period and found that all functions including the passive cooling are working as expected. The MIRIS has a wide-field of view $3.67{\times}3.67$ degrees and wavelength coverage from 0.9 to 2.0 micro-meter with the angular resolution of 51.6 arcsec. The main science missions of the MIRIS are (1) mapping of the Galactic plane with Paschen-alpha line (1.88 micro-meter) for the study of warm interstellar medium and (2) the measurement of large angular fluctuations of cosmic near infrared background radiation with I (1.05 micro meter) and H (1.6 micro meter) bands to identify their origin. We present the results of MIRIS initial operation in this paper.

• Journal of Radiation Protection and Research
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• v.41 no.3
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• pp.185-190
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• 2016

Background: In order to measure neutron energy spectra, the conventional Bonner Sphere Spectrometers (BSS) are widely used. In this spectrometer, several measurements with different size Bonner spheres are required. Operators should, therefore, place these spheres in several times to a measurement point where radiation dose might be relatively high. In order to reduce this effort, novel neutron energy spectrometer using an onion-like single Bonner sphere was proposed in our group. This Bonner sphere has multiple sensitive spherical shell layers in the single sphere. In this spectrometer, a band-shaped thermal neutron detection medium, which consists of a LiF-ZnS mixed powder scintillator sheet and a wavelength-shifting (WLS) fiber readout, was looped to each sphere at equal angular intervals. Amount of LiF neutron converter is reduced near polar region, where the band-shaped detectors are concentrated, in order to uniform the directional sensitivity. The LiF-ZnS mixed powder has an advantage of extremely high light yield. However, since it is opaque, scintillation photons cannot be collect uniformly. This type of detector shows no characteristic shape in the pulse height spectrum. Subsequently, it is difficult to set the pulse height discrimination level. This issue causes sensitivity fluctuation due to gain instability of photodetectors and/or electric modules. Materials and Methods: In order to solve this problem, we propose to replace the LiF-ZnS mixed powder into a flexible and Transparent RUbber SheeT type $LiCaAlF_6$ (TRUST LiCAF) scintillator. TRUST LiCAF scintillator can show a peak shape corresponding to neutron absorption events in the pulse height spectrum. Results and Discussion: We fabricated the prototype detector with five sensitive layers using TRUST LiCAF scintillator and conducted basic experiments to evaluate the directional uniformity of the sensitivity. Conclusion: The fabricated detector shows excellent directional uniformity of the neutron sensitivity.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.51.1-51.1
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• 2014

DOTIFS is a new multi-object Integral Field Spectrograph (IFS) being designed and fabricated by the Inter-University Center for Astronomy and Astrophysics, Pune, India, (IUCAA) for the Cassegrain side port of the 3.6m Devasthal Optical Telescope (DOT). The telescope is constructed by the Aryabhatta Research Institute of Observational Sciences, Nainital (ARIES). Its main scientific objectives are the physics and kinematics of the ionized gas, star formation and H II regions in nearby galaxies. It is a novel instrument in terms of multi-IFU, built in deployment system, and high throughput. It consists of one magnifier, 16 integral field units (IFUs), and 8 spectrographs. Each IFU is comprised of a microlens array and 144 optical fibers, and has $7.4^{\prime\prime}{\times}8.7^{\prime\prime}$ field of view with 144 spaxel elements with a sampling of 0.8" hexagonal aperture. The IFUs can be deployed on the telescope side port over an 8' diameter focal plane by x-y actuators. 8 Identical, all refractive, dedicated fiber spectrographs will produce 2,304 R~1800 spectra over 370-740nm wavelength range with single exposure. Currently, conceptual and baseline design review had been done, and is in the critical design phase with a review planned for later this year. Some of the components have already arrived. The instrument will see its first light in 2015.

• 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.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.05a
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• pp.271-274
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• 2002

In this study, we fabricated the semiconductor laser for optical sensor with 1.55${\mu}{\textrm}{m}$wavelength region. In order to suppress lasing oscillation and to reduce the reflectivity, the devices of bending type were designed and fabricated. Their output power were 1.6㎽ at a pulse drive current of 100㎃. When the fabricated device was applied to optical fiber gyroscope, the output power of optical fiber was 540㎻ at a CW drive current of 100㎃, the full width at half maximum spectral width was 53nm. And the random-walk coefficient was measured to be 2.5$\times$10­$^3$deg/√hr, the gyro output drift was also found to be 0.3 deg/hr. So we confirmed the possibility of application to use for light source of optical fiber gyroscope.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.3 no.3
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• pp.681-686
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• 1999

In this study, the gain characteristics of the strained structures for SOA were calculated numerically and the optimized strained quantum well for the polarization-insensitive SOA was obtained. The structures used in this calculation were consisted of one, two, and three GaAs Delta layers respectively in the GaInAs(160 $\AA$) well. Moreover the third one was calculated by changing from one mono-layer to three mono-layers in the thichless of GaAs delta layers. This structure enhances the TM mode gain coefficient with good efficiency because the light-hole band is lifted up whereas the heavy-hole band is lowered down. Additionally, The structure of the 3 GaAs delta layers(1 mono layer thickness) shows 3dB gain bandwidth of 85nm in 1.55um wavelength system. This study is expected to be used in making a wide band and polarization-independent semiconductor optical amplifier practically.