• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.64-65
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• 2007

High-efficiency white organic light-emitting diodes (WOLEDs) were fabricated with two emissive layers and exciton blocking layer was sandwiched between two phosphorescent dyes which were, bis(3,5-Difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl) iridium III (Flrpic) as blue emission and a newly synthesized red phosphorescent material guest, Bis(5-benzoyl-2-phenylpyridinato-C,N)iridium(III) (acetylacetonate) ((Bzppy)2Ir(III)acac). This exciton blocking layer prevents a triple-triple energy transfer between the two phosphorescent emissive layers with balanced emission of blue and red. The white device showed the Commission Internationale d'Eclairage (CIEx,y) coordinates of (0.34, 0.40) at the maximum luminance of $24100\;cd/m^2$ and maximum luminous efficiency of 22.4 cd/A, respectively.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2007년도 7th International Meeting on Information Display 제7권1호
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• pp.137-140
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• 2007

We prepared ambipolar organic field-effect transistors and observed blue emission when both hole and electron accumulation layers were in the channel. We found that the reduction of carrier traps and controlling devices' preparation and measurement conditions were crucial for ambipolar operation.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2008년도 International Meeting on Information Display
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• pp.435-438
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• 2008

We demonstrated the efficient blue organic light-emitting diodes (OLEDs) by employing diarylamino-fluorene derived blue fluorescent molecules as dopants. Among those, a device exhibited blue emission with the luminous efficiency of 11.2 cd/A at $20\;mA/cm^2$, the external quantum efficiency of 9.7% at $20\;mA/cm^2$, and the $CIE_{x,y}$ coordinates of (x=0.163, y=0.259) at 8V.

• 한국전기전자재료학회논문지
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• 제22권4호
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• pp.323-326
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• 2009

We have developed blue-emitting phosphorescent organic light emitting diodes (OLEDs) using 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) and tris (8-quinolinolato)aluminum ($Alq_3$) electron transport layers. As blue dopant and host materials, bis[(4,6-di-fluorophenyl)-pyridinate-N,C2']picolinate (FIrpic) and N,N'-dicarbazolyl-3,5-benzene (mCP) were used, respectively. The driving voltage, current efficiency and emission characteristics of devices were investigated. While the driving voltage was about $1{\sim}2$ V lower in the device with an $Alq_3$ layer, the current efficiency was about 66 % higher in the device with BCP electron transport layer. the blue phosphorescent OLED with BCP layer exhibited higher purity of color, resulting from a relatively weak electroluminescence intensity at 500 nm.

• 전기화학회지
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• 제1권1호
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• pp.24-27
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• 1998

Electroluminescence (EL) comes from the light emission obtained by the electrical excitation energy passing through a phosphor layer undo. an applied high electrical field $(10^6 V/cm)$. The preparation of white and blue phosphors and characterizations of light emitting alternating current powder electroluminescent devices (ACPELDs) were investigated. In this work, we fabricated two kinds of ELDs, that is, yellow electroluminescent device (B-ELD), blue electroluminescent device (B-ELD). The basic st.uctures of Y-ELD and B-ELD are ITO (Indium Tin Oxide)/phosphor layer/Insulator layer/Carbon electrode and ITO/Phosphor layer/Insulating layer/carbon electrode, respectively. Another structures of ITO/Phosphor and Insulator mixture layer/Backelectrode are introduced. EL spectra and luminance of two types of ELDs were measured by changing voltage at fixed frequency 0.4kHz, 1.5kHz. Blue and yellow phosphors prepared in this work show $50cd/m^2\;and\;30cd/m^2$ of luminance at 400Hz, 150V.

• 한국전기전자재료학회논문지
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• 제19권6호
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• pp.568-573
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• 2006

We have synthesized new blue light emitting random copolymers, poly(9,9'-n-dioctylfluorene-co-perfluorobenzene-1,4-diyl)s (PFFBs), via Ni(0)-mediated coupling reactions. The weight-average molecular weights ($M_w$) of the PFFB copolymers ranged from 9,000 to 15,000. The PFFB copolymers dissolved in common organic solvents such as THF and toluene. The PL emission peaks of the PFFB copolymers were at around 420, 440, and 470 nm. EL devices were fabricated in ITO/PEDOT/polymer/Ca/Al configurations using these polymers. These EL devices were found to exhibit pure blue emission with approximate CIE coordinates of (0.15, 0.11) at $100cd/m^2$. The blue emissions of these devices might be due to the restriction of the polymer chains to aggregation by introducing of the highly electronegative fluorine moieties. The maximum brightnesses of the PFFB copolymer devices ranged from 140 to $3600cd/m^2$ with maximum efficiencies from 0.2 to 0.6 cd/A. The enhanced efficiency of the PFFB (8/2) copolymer device results from the inhibition of excimer formation by the introduction of the electronegative fluorine moieties into the copolymers.

• Journal of Biosystems Engineering
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• 제35권2호
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• pp.124-131
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• 2010

Chlorophyll fluorescence has been researched for assessing fruit post-harvest quality and condition. The objective of this preliminary research was to investigate the potential of fluorescence spectroscopy for measuring apple fruit quality. Ultraviolet (UV) and blue light was used as an excitation source for inducing fluorescence in apples. Fluorescence spectra were measured from 'Golden Delicious' (GD) and 'Red Delicious' (RD) apples using a visible/near-infrared spectrometer after one, three, and five minutes of continuous UV/blue light illumination. Standard destructive tests were performed to measure fruit firmness, skin and flesh color, soluble solids and acid content from the apples. Calibration models for each of the three illumination time periods were developed to predict fruit quality indexes. The results showed that fluorescence emission decreased steadily during the first three minutes of UV/blue light illumination and was stable within five minutes. The differences were minimal in the model prediction results based on fluorescence data at one, three or five minutes of illumination. Overall, better predictions were obtained for apple skin chroma and hue and flesh hue with values for the correlation coefficient of validation between 0.80 and 0.90 for both GD and RD. Relatively poor predictions were obtained for fruit firmness, soluble solids content, titrational acid, and flesh chroma. This research has demonstrated that fluorescence spectroscopy is potentially useful for assessing selected quality attributes of apple fruit and further research is needed to improve fluorescence measurements so that better predictions of fruit quality can be achieved.

• 한국전기전자재료학회논문지
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• 제22권6호
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• pp.512-515
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• 2009

We have fabricated blue phosphorescent organic light emitting diodes (PHOLEDs) using a 3,5'-N,N'-dicarbazole-benzene (mCP) host and iridium (III) bis[(4,6-difluorophenyl)-pyridinato-N,$C^{2'}$] picolinate (Flrpic) guest materials, The Flrpic was partially doped into the mCP host layer, for investigating recombination zone, current efficiency, and emission characteristics of the blue PHOLEDs. The recombination of electrons and holes takes place inside the mCP layer adjacent to the mCP/hole blocking layer interface. The best current efficiency was obtained in a device with an emission layer structure of mCP (10 nm)/mCP:Flrpic (20 nm, 10%). The high current efficiency in this device was attributed to the confinement of Ffrpic triplet excitons by the undoped mCP layer with high triplet energy, which blocks diffusion of Ffrpic excitons to the adjacent hole transport layer with a lower triplet energy.

• Journal of Biosystems Engineering
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• 제24권2호
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• pp.115-122
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• 1999

Because of their small mass, volume, solid state construction and long life, light-emitting diodes(LEDs) hold promises as a lighting source for intensive plant production system. Spectral characteristics and light intensity of LEDs were tested to investigate their feasibility as artificial lighting sources for growth and morphogenesis control in transplant production system. Blue, green, and red LEDs had a peak-emission wavelength at 442nm, 522nm, and 673nm, respectively. Their half width defined as the difference between upper and lower wavelength in the intensity equivalent to 50% of the maximum intensity showed 26nm, 41nm, and 74nm, respectively. Photosynthetic photon flux(PPE) at the distance of 9cm under the LEDs array was measured as $235{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$ for red, $109{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$ for green, and $75{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$ for blue LEDs. At the same distance, green LEDs had the illuminance of 13,0001x, nine to ten times higher than those of red and blue LEDs. Red, green, and blue LEDs at a distance of 9cm had the irradiance of $46W{\cdot}m^{-2},\;19W{\cdot}m^{-2},\;8W{\cdot}m^{-2}$, respectively. Light intensity of blue, green, and red LEDs increased linearly in proportion to the magnitude of the current applied to the operating circuit. Thus the light intensity of LEDs was controlled by the applied current in operating circuit.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2003년도 International Meeting on Information Display
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• pp.928-931
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• 2003

In order to realize full color display, two approaches were used. The first method is the patterning of red, green, and blue emitters using a selective deposition. Another approach is based on a white-emitting diode, from which the three primary colors could be obtained by micro-patterned color filters. White-light-emitting organic light emitting devices (OLEDs) are attracting much attention recently due to potential applications such as backlights in liquid crystal displays (LCDs) or other illumination purposes. In order for the white OLEDs to be used as backlights in LCDs, the light emission should be bright and have Commission Internationale d'Eclairage (CIE) chromaticity coordinates of (0.33, 0.33). For obtaining white emission from OLEDs, different colours should be mixed with proper balances even though there are a few different methods for mixing colors. In this study, we will report a white organic electroluminescent device using exciton diffusion length concept.