• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.537-539
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• 2006

We developed an 4.5" $192{\times}64$ active matrix organic light-emitting diode display on a glass using organic thin-film transistor (OTFT) switching-arrays with two transistors and a capacitor in each sub-pixel. The OTFTs has bottom contact structure with a unique gate insulator and pentacene for the active layer. The width and length of the switching OTFT is $800{\mu}m$ and $10{\mu}m$ respectively and the driving OTFT has $1200{\mu}m$ channel width with the same channel length. On/off ratio, mobility, on-current of switching OTFT and on-current of driving OTFT were $10^6,0.3{\sim}0.5\;cm^2/V{\cdot}sec$, order of 10 ${\mu}A$ and over 100 ${\mu}A$, respectively. AMOLEDs composed of the OTFT switching arrays and OLEDs made using vacuum deposition method were fabricated and driven to make moving images, successfully.

• Korean Chemical Engineering Research
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• v.43 no.5
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• pp.616-620
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• 2005

The morphology and photoluminescence characteristics of green light emitting hexaaluminate phosphor particles prepared by high temperature spray pyrolysis from spray solution with and without ammonium dihydrogen phosphate flux were investigated. The particles prepared from spray solution without flux material had hollow morphology at preparation temperatures between $900^{\circ}C$ and $1,650^{\circ}C$. Ammonium dihydrogen phosphate flux added into spray solution enabled the formation of particles with spherical shape and filled morphology at preparation temperatures between $900^{\circ}C$ and $1,650^{\circ}C$. The hexaaluminate phosphor particles with magnetoplumbite structure were directly prepared by spray pyrolysis from spray solution with ammonium dihydrogen phosphate flux above $1,600^{\circ}C$. Ammonium dihydrogen phosphate flux was effective in improving the photoluminescence intensity of the phosphor particles at low preparation temperatures. The phosphor particles prepared from spray solution with and without flux material by spray pyrolysis under reducing atmosphere at $1,650^{\circ}C$ had comparable photoluminescence intensities with that of the phosphor particles optimized by post-treatment.

• Journal of the korean academy of Pediatric Dentistry
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• v.47 no.1
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• pp.70-77
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• 2020

The present study is aimed to assess the effect of antimicrobial photodynamic therapy (aPDT) on Streptococcus mutans biofilm through teeth whitening light emitting diode (LED). Planktonic and dynamic biofilm state cultures of S. mutans were used. Erythrosine 20 μM/L was used as the photosensitizer. Irradiation was performed by exposing cultures to clinic and homecare whitening LEDs for 15 minutes. The viability was measured through Colony Forming Unit counts and confocal laser scanning microscopy. aPDT using whitening LEDs and erythrosine significantly decreased the CFU count of S. mutans compared to that in the control group. Dynamic biofilm group showed more resistant features to aPDT compared with planktonic state. Clinic and homecare whitening LED device showed similar antimicrobial effect. The whitening LED, which could irradiate the entire oral arch, showed a significant photodynamic effect on cariogenic S. mutans biofilm. aPDT mediated by erythrosine and LEDs used for teeth whitening exhibited promising antimicrobial activity.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.5
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• pp.97-105
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• 2017

An air-burst munition is limited in space, so there is a limit on the size of the fuze and the amount of ammunition. In order to increase a firepower to a target with limited ammunition, it is necessary to concentrate the firepower on the ground instead of the omnidirectional explosion after flying to the target. This paper explores the design and verification of a ground-detection sensor that detects the direction of the ground and determines the flight-distance of an air-burst munition using a single axis geomagnetic sensor. Prior to the design of the ground detection sensor, a geomagnetic sensor model mounted on the spinning air-burst munition is analyzed and a ground-detection algorithm by simplifying this model is designed. A high speed rotating device to simulate a rotation environment is designed and a geomagnetic sensor and a remote-recording system are fabricated to obtain geomagnetic data. The ground detection algorithm is verified by post-processing the acquired geomagnetic data. Taking miniaturization and low-power into consideration, the ground detection sensor is implemented with analog devices and the processor. The output signal of the ground detection sensor rotating at an arbitrary rotation speed of 200 Hz is connected to the LED (Light Emitting Diode) in the high speed rotating device and the ground detection sensor is verified using a high-speed camera.

• Journal of the Korean Chemical Society
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• v.50 no.3
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• pp.237-242
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• 2006

Nowadays, LEDs has been applied to the luminescent devices of various fields because of the invention of high efficient blue chip. Recently, especially, the white LEDs composed of InGaN blue chips and a yellow phosphor (YAG:Ce3+) have been investigated extensively. With the exception of YAG:Ce3+ phosphor, however, there are no reports on yellow phosphor that has significant emission in the 450~470 nm excitation range and this LED system is the rather low color rendering index due to their using two wavelength. Hence, we have attempted to synthesize thiogallate phosphors that efficiently under the long wavelength excitation range in the present case. Among those phosphors, we have synthesized Sr2Ga2S5:Eu2+ phosphor by change the host material of SrGa2S4:Eu2+ which is well known phosphor and we investigated the luminescent properties. In order to obtain the harmlessness and simplification of the synthesis process, sulfide materials and mixture gas of 5 % H2/95 % N2 were used instead of the CS2 or H2S gas. The prepared phosphor shows the yellow color peaking at the 550 nm wavelength and it possible to emit efficiently under the broad excitation band in the range of 300~500 nm. And this phosphor shows high luminescent intensity more than 110 % in comparison with commercial YAG:Ce3+ phosphor and it can be applied for UV LED due to excitation property in UV region.

• Journal of dental hygiene science
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• v.15 no.4
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• pp.393-398
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• 2015

One of the most critical causes in determining the clinical outcomes of dental prostheses is the validity of models. However, studies that evaluated validity of digital models are few. The objectives of this study were to evaluate validity of edentulous digital models for full denture fabrication. Twenty stone models (edentulous model) were manufactured and scanned by dental blue light emitting diode scanner. Twenty digital models were manufactured. Six linear distances (inter-canine distance, inter-molar distance, two dental arch lengths (right, left), two diagonal of dental arch lengths (right, left) were measured for validity evaluation. The measurements of distances of stone models were used by digital vernier caliper and digital models were used by computer program. The mean${\pm}$deviations values of six distances were calculated. The means were compared by the Mann Whitney U test (${\alpha}=0.05$). All statistical analysis were performed using IBM SPSS Statistics ver. 20.0. Although digital models were smaller than stone models in six distances, there were no significant differences (p>0.05) and non exceeded the clinical acceptable range. The edentulous digital models for full denture fabrication can be considered clinically acceptable.

• The Journal of Engineering Geology
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• v.30 no.1
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• pp.17-30
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• 2020

An optical televiewer is a geophysical logging device that produces continuous high-resolution full-azimuth images of a borehole wall using a light-emitting-diode and a complementary metal-oxide semiconductor image sensor to provide valuable information on subsurface discontinuities. Recently, borehole imaging logging has been applied in many fields, including ground subsidence monitoring, rock mass integrity evaluation, stress-induced fracture detection, and glacial annual-layer measurements in polar regions. Widely used commercial borehole imaging logging systems typically have limitations depending on equipment specifications, meaning that it is necessary to clearly verify the scope of applications while maintaining appropriate quality control for various borehole conditions. However, it is difficult to directly check the accuracy, implementation, and reliability for outcomes, as images derived from an optical televiewer constitute in situ data. In this study, we designed and constructed a modular fractured borehole model having similar conditions to a borehole environment to report unprecedented results regarding reliable data acquisition and processing. We investigate sonde magnetometer accuracy, color realization, and fracture resolution, and suggest data processing methods to obtain accurate aperture measurements. The experiment involving the fractured borehole model should enhance not only measurement quality but also interpretations of high-resolution and reliable optical imaging logs.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.3
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• pp.199-204
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• 2000

In this study, the ZnS nanosized thin films that could be used for fabrication of blue light-emitting diodes, electro-optic modulators, and n-window layers of solar cells were grown by the solution growth technique (SGT), and their structural and optical properties were examined. Based on these results, the quantum size effects of ZnS were systematically investigated. Governing factors related to the growth condition were the concentration of precursor solution, growth temperature, concentration of aq. ammonia, and growth duration. X-ray diffraction patterns showed that the ZnS thin film obtained in this study had the cubic structure ($\beta$-ZnS). When the growth temperature was $75^{\circ}C$, the surface morphology and the grain size uniformity were the best. The energy band gaps of samples were determined from the optical transmittance valued, and were shown to vary from 3.69 eV to 3.91 eV. These values were substantially higher than 3.65 eV of bulk ZnS, demonstrating that the quantum size effect of SGT grown ZnS is remarkable. Photoluminescence (PL) peaks were observed at the positions corresponding to the lower energy than that to energy band gap, illustrating that the surface states were induced by the ultra-fineness of grains in ZnS films. Particularly, for the first time, it is reported for the SGT grown ZnS that the PL peaks were shifted depending on the grain size.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.1
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• pp.18-21
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• 2017

In this study, spherical monodispersed cerium-doped yttrium aluminum garnet (YAG : $Ce^{3+}$) phosphor particles were synthesized via homogeneous precipitation method using the mixed solution of yttrium nitrate, cerium nitrate, aluminum nitrate, ammonium aluminum sulfate, and urea as a precipitant. During the process of precursors of monodispersed YAG : $Ce^{3+}$, aluminum ions which form spherical aluminum compounds precipitated first and yttrium compounds precipitated onto the surface of the existing spherical aluminum compounds. Drying process using lyophilization could obtain monodispered spherical YAG : $Ce^{3+}$ particles compare to using oven. The thermal calcination process of YAG : $Ce^{3+}$ precursors under the temperature of $1200^{\circ}C$ for 6 h was enough to obtain 400~500 nm sized YAG particles with pure YAG phase.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.5
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• pp.12-18
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• 2008

Ag paste was employed for source and drain electrode of OTFTs and for the data metal lines of OTFT-OLED array on PC(polycarbonate) substrate. We tested two kinds of Ag-pastes such as pastes for 325 mesh and 500 mesh screen mask to examine the pattern ability and electrical performance for OTFTs. The minimum feature size was 60 ${\mu}m$ for 325 mesh screen mask and 40 ${\mu}m$ for 500 mesh screen mask. The conductivity was 60 $m{\Omega}/\square$ for 325 mesh and 133.1 $m{\Omega}/\square$ for 500 mesh. For the OTFT performance the mobility was 0.35 $cm^2/V{\cdot}sec$ and 0.12 $cm^2/V{\cdot}sec$, threshold voltage was -4.7 V and 0.9 V, respectively, and on/off current ratio was ${\sim}10^5$, for both screen masks. We applied the 500 mash Ag paste to OTFT-OLED array because of its good patterning property. The pixel was composed of two OTFTs and one capacitor and one OLED in the area of $2mm{\times}2mm$. The panel successfully worked in active mode operation even though there were a few bad pixels.