• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.1
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• pp.40-46
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• 2019

To study the frequency response characteristics of alternating-current-driven organic light-emitting diodes (OLEDs), we fabricated blue-fluorescent OLEDs and analyzed their electroluminescent characteristics according to the alternating current voltage and frequency. The luminance-frequency characteristics of alternating-current-driven OLED was similar to that of a low-pass filter, and the luminance of high-voltage OLED decreased at higher frequency than low-voltage OLED. The luminance characteristics of the OLED according to the frequency is due to the capacitive reactance in the OLED, generated during the alternating current driving. The frequency response characteristics of the OLED according to the voltage is due to the decrease in internal resistance of the organic layer. In addition, the negative voltage component of the alternating current did not affect the frequency response of the OLED. Therefore, the electroluminescent characteristics of OLED with an alternating current power of 60 Hz are not influenced by the frequency.

• Ceramist
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• v.22 no.3
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• pp.218-229
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• 2019

The development of highly efficient thermally activated delayed fluorescence (TADF) materials is an active area of recent research in organic light emitting diodes (OLEDs) since the first report by Chihaya Adachi in 2011. Traditional fluorescent materials can harvest only singlet excitons, leading to the theoretically highest external quantum efficiency (EQE) of 5% with considering about 20% light out-coupling efficiency in the device. On the other hand, TADF materials can harvest both singlet and triplet excitons through reverse intersystem crossing (RISC) from triplet to singlet excited states. It could provide 100% internal quantum efficiencies (IQE), resulting in comparable high EQE to traditional rare-metal complexes (phosphorescent materials). Thanks to a lot of efforts in this field, many highly efficient TADF materials have been developed. This review focused on recent molecular design concept and optoelectronic properties of TADF materials for high efficiency and long lifetime OLED application.

• 한국정보디스플레이학회:학술대회논문집
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• 2003.07a
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• pp.903-906
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• 2003

Doping a small amount of a phosphorescent dye into an organic light-emitting diodes(OLED) can lead to a significant improvement in the device properties. The fluorescent host materials like TAZ, CBP have been used, but have a problem of rapid decay of efficiency at high current densities. To alleviate this problem, phosphorescent host was introduced. The whole configuration of OELD fabricated was ITO/a-NPD(50nm)/Zn $cluster:Ir(ppy)_{3}(30nm)/BCP{(10nm)/Alq_{3}(20nm)$ /Al:Li. The OLED showed high luminance (> 50,000 $cd/m^{2}$ ) and external efficiency(5.7%). At higher current densities, rapid decay of external quantum efficiency or host emission, which was frequently observed in the fluorescent host system, were not observed.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2003.05a
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• pp.369-369
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• 2003

Hemocytes in marine bivalves play important immunological roles in discrimination, opsonization and phagocytosis of foreign materials as a defense mechanism. In this study we report the flow cytometric implications to investigate the immune parameters such as the compositional and the functional characteristics of hemocytes isolated from the Manila clams, Ruditapes philippinarum. Heterogeneity of the hemocytic cell population was determined by the forward scatter (FSC) and side scatter (SSC) cytometric profile which showed three populations: granulocytes, hyalinocytes and small agranular cells. In addition, phagocytosis rate was measured after adding fluorescent-labeled particles. The data were initially analysed for two-parameters: FSC and SSC, then the fluorescent (FL 1) frequency distribution histogram of the hemocyte population was subsequently obtained.

• Bulletin of the Korean Chemical Society
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• v.35 no.1
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• pp.277-279
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• 2014

• Bulletin of the Korean Chemical Society
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• v.29 no.5
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• pp.943-947
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• 2008

A phosphate-specific and fluorescent probe was prepared for label-free phosphatase assays based on fluorescence polarization. By using the probe, dephosphorylation reactions of DNA and protein substrates by calf intestinal alkaline phosphatase (CIP) could effectively be monitored in real-time. Since this assay method does not require additional materials such as labeled substrates and phosphospecific antibodies to obtain fluorescence polarization signals, it is simple, cost-effective, and expected to be useful not only for measuring activity of phosphatases but also for high-throughput screening of phosphatase inhibitors.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2688-2691
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• 2008

This study addresses a microfluidic method to uniformly form diacetylene (DA) liposomes and control their size. DA liposomes are biochemical sensor materials with a unique property such that when they are polymerized to polydiacetylene (PDA) they exhibit non-fluorescent blue to fluorescent red phase transition upon chemical or thermal stress. The liposome size and distribution are important because they significantly affect the phase transition. So far, DA Liposomes, have been prepared by mixing of bulk phases leading to heterogeneous, polydisperse distribution in size. Therefore, additional post-processes are required such as sonication or membrane extrusion to obtain an appropriate size of liposomes. Here, we report a novel strategy using a microfluidic chip and hydrodynamic focusing to form DA liposomes and control their size. Preliminary results obtained by scanning electron microscope (SEM) and dynamic light scattering (DLS) show that the microfluidic strategy generates more monodispersed liposomes than a bulk method.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.815-818
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• 2002

Mn doped hexagonal phase of ZnS has been studied as a yellow-orange phosphor for the application to fluorescent displays operated at low voltages. It was found that luminescence from $Mn^{2+}$ was increased as the Mn concentration was increased up to1.2 mol% of host lattice. This study has been attempted by adding trivalent ions such as $Al^{3+}$ or $Bi^{3+}$ to ZnS:Mn as an agent to do the efficient incorporation of Mn ions into ZnS:Mn lattice, resulting in a significant improvement in the phosphor performance, especially at low voltages.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.628-631
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• 2007

We developed new green emitting materials based on the spiro moieties. The introduction of a spiro linkage into the structure of DJGH series lead to a reduction in crystallization tendency and an increase in glass transition temperature. they showed much better emitting efficiency and color purity than commercial host material $Alq_3$.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.12
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• pp.3540-3545
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• 2009

Due to recent development of high temperature high pressure(HTHP) diamond synthetic and treatment technology, we need to identify the natural diamonds fast, reliable, and economically. We proposed using new method of UV fluorescence and X-ray Lang topography imaging for distinguishing one synthetic diamond from four natural colored diamonds. We observe unique local stress field uneven image in synthetic diamond using UV fluorescence and Lang topography characterization, while uniform images in natural diamonds. Especially, X-ray Lang method offered the better identification power with better high resolution on stress field images.