• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05b
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• pp.90-93
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• 2002

In the surface pressure-area isotherms of mixed monolayers, mixtures containing as much as 30 mol% of AA form stable condensed monolayer while the monolayer without AA is in the expanded state because PVK take on 3D collapsed. All of the mixed monolayers with 0, 10, 20 and 30 mol% of AA could be readily transferred onto ITO substrate at 16, 17, 24 and 26 mN/m, respectively. The monolayer containing 30 mol% of AA, however, showed a roughness value of 28A and became homogeneous decreasing with the phase separation. We fabricated organic EL device of ITO/CuPc/MEL/BBOT/iLiF/Al using mixed monolayer of 13, 19 and 25 layer deposited by LB method as a emitting layer. In the voltage-current characteristics of EL device, current density was much smaller than that of the spin-coated devices. It may due to the large contact resistance existed at the interface of LB layer/organic layer inhibit carrier injection to the emitting layer. EL spectra of device showed peaks at 450. 470, 505, 555 and 650 nm and the white light emission indicate the CIE coordinate x=0.306, y=0.353.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.1
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• pp.53-56
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• 2007

We have fabricated organic white light emitting diodes by mixing two colors from very thin rubrene doped and non-doped DPVBi layers. The device structure was ITO/2-TNATA(15 nm)/${\alpha}$-NPD(35 nm)/DPVBi:rubrene(5 nm)/DPVBi(30 nm)/$Alq_{3}(5\;nm)$/BCP(5 nm)/LiF(0.5 nm)/Al(150 nm). The yellow-emitting rubrene of 0.7 wt % was doped into the blue-emitting DPVBi host for the white light. CIE coordinate of the device was (0.31, 0.33) at 8 V. The color coordinates were stable at wide ranges of driving voltages. The luminance was over $1,000\;cd/m^{2}$ at 8 V and increases to $14,500\;cd/m^{2}$ at 12 V. The maximum current efficiency of the device was 8.2 cd/A at $200\;cd/m^{2}$.

• 한국정보디스플레이학회:학술대회논문집
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• 2001.08a
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• pp.209-212
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• 2001

We report the synthesis and characterization of new alkoxy substituted spirobifluorene derivatives. The spiro compounds having alkoxy hydrocarbon chains were readily soluble in common organic solvents, having improved film-forming properties and had a significantly reduced tendency to crystallize, resulting in increasing their service lifetime. The results of DSC showed that it was amorphous. The optical and electroluminescent spectra were characterized. Electroluminescence (EL) properties of three-layer light emitting diodes (LED) of $ITO/TPD/spirobifluorene/Alq_3/LiF/Al$ as the active layer were characterized. Blue emission peaking of the EL spectrum of the three-layer device at 402 nm and a luminance of 3,125 $cd/m^2$ were achieved at a drive voltage 12.8 V. The luminous efficiency was obtained to be 1.7 lm/W. The color coordinate in CIE chromaticity is (0.16, 0.09), which is in a pure blue region. The external quantum efficiency was obtained to be 2.0%. The results indicate that the spirobifluorene compounds having alkoxy hydrocarbon chains are strongly potential blue emitters for LED applications.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.956-960
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• 2006

Deep-blue organic light-emitting diodes (OLEDs) with/without ultra-thin LiF layer inserted at the interface between hole-blocking and electron-transporting layers have been fabricated and investigated. The fundamental structures of the OLEDs are ITO/m-MTDATA/NPB/BCP/LiF (with/ without)/ $Alq_3/LiF/Al.Deep$ blue light emission with CIE coordinate of (0.15, 0.11) has been achieved for all devices. Further, by inserting LiF with thickness of 1nm at the interface between BCP and $Alq_3$ layer, the luminous efficiency as well as the power efficiency is much improved compared to that without. The enhancement of electron injection due to insertion of LiF may account for this improvement.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.6
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• pp.456-461
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• 2012

We studied the emission characteristics of white phosphorescent organic light-emitting diodes (PHOLEDs), which were fabricated using a two-wavelength method. To optimize emission characteristics of white PHOLEDs, white PHOLEDs with red/blue, blue/red and red/blue/red emitting layer (EML) structures were fabricated using a host-dopant system. In case of white PHOLEDs with red/blue structure, the best efficiency was obtained at a structure of red (15 nm)/blue (15 nm). But the emission color was blue-shifted white. In case of white PHOLEDs with blue/red structure, the better color purity and efficiency were observed at a blue (29 nm)/red (1 nm) structure. For additional improvement of color purity in white PHOLEDs with blue (29 nm)/red (1 nm) EMLs, we fabricated white PHOLEDs with red (1 nm)/blue (28 nm)/red (1 nm) structure. The current efficiency, external quantum efficiency, and CIE (x, y) coordinate were 27.2 cd/A, 15.1%, and (0.382, 0.369) at 1,000 $cd/m^2$, respectively.

• Applied Science and Convergence Technology
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• v.27 no.3
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• pp.52-55
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• 2018

We reported a new method to enhance the photoluminescence (PL) properties of $Eu^{3+}$ ions doped $Gd_2Mo_4O_{15}$ phosphors via cation substitution. With the aid of conventional sol-gel method, a series of $Eu^{3+}$ ions doped $Gd_{2(1-x)}Y_{2x}Mo_4O_{15}$ phosphors were prepared. The prepared samples emitted red light when excited at 393 nm. Moreover, when part of the $Gd^{3+}$ ions was substituted by the $Y^{3+}$ ions, the PL emission intensity of the studied samples was enhanced and the optimal doping concentration for $Y^{3+}$ ions was 30 mol%. The calculated CIE coordinate (0.663,0.337) was situated in the red region. Furthermore, the thermal quenching behaviors of the synthesized $Eu^{3+}$ ions doped $Gd_{2(1-x)}Y_{2x}Mo_4O_{15}$ phosphors were studied. At last, we also packaged a red-emitting light-emitting diode device by integrating the obtained phosphors and a near-ultraviolet chip to verify the applications of the $Eu^{3+}$ ions doped $Gd_{2(1-x)}Y_{2x}Mo_4O_{15}$ phosphors for indoor lighting.

• Journal of Information Display
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• v.11 no.3
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• pp.123-127
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• 2010

Fluorescent white organic light-emitting diodes showing high color-rendering indices (CRIs) of up to 81 was demonstrated, with a silicon-cored anthracene derivative (PATSPA) doped with DPAVBi utilized as the deep-blue host and dye materials, and the commercial dyes rubrene and DCM2 utilized as the orange- and red-light-emitting dyes. The devices, consisting of three emissive layers, showed bright-white-light emission, but the ratio of the blue peak to the orange and red peaks changed with the current density and the thickness of the blue emissive layer. A high CRI was achieved with the use of a deep-blue emitter doped in a novel host and by optimizing the blue-layer thickness. The device with a blue-layer thickness of 10 nm showed the Commission Internationale de l'Eclairage (CIE) color coordinate of (0.33, 0.35), a high CRI of 81, and a moderate external quantum efficiency of 2% at a current density of $2.5\;mA/cm^2$.

• Journal of Information Display
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• v.3 no.2
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• pp.6-12
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• 2002

In order to achieve white emission from organic light emitting devices (OLEDs), five distinct structures were fabricated and tested. The white emission was obtained using two different color-emitting materials (yellow from rubrene-doped $Alq_3$ and blue from DPVBi) with or without a carrier-blocking layer. For enhancing the red emission, two types of devices with three-color emitting materials were fabricated. The white emission, close to the CIE coordinate of (0.3,0.3), was achieved by using two blocking layers as well that as without a blocking layer. This paper covers the subject of controlling the location of exciton recombination zone. It has been found that there is a trade-off in that the devices with three color emitting layers do not show as much luminescence efficiency compared to those with two color emitting layers, but rather, show distinct red emission in the resultant emission spectra. The highest power efficiency was measured to be 1.15lm/W at 2,000 $cd/m^2$ for a structure with two color-emitting layers.

• Bulletin of the Korean Chemical Society
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• v.35 no.1
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• pp.189-196
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• 2014

Water dispersible ZnS based nanocrystals: ZnS (blue), ZnS:Cu (green) and ZnS:Mn (yellow-orange) were synthesized by capping the surface of the nanocrystals with a mercaptopropionic acid (MPA) molecule. The MPA capped ZnS based nanocrystal powders were characterized by using XRD, HR-TEM, EDXS, FT-IR, and FT-Raman spectroscopy. The optical properties of the colloidal nanocrystals were also measured by UV/Vis and photoluminescence (PL) spectroscopies in aqueous solvents. The PL spectra showed broad emission peaks at 440 nm (ZnS), 510 nm (ZnS:Cu) and 600 nm (ZnS:Mn), with relative PL efficiencies in the range of 4.38% to 7.20% compared to a reference organic dye. The measured average particle sizes from the HR-TEM images were in the range of 4.5 to 5.0 nm. White light emission was obtained by mixing these three nanocrystals at a molar ratio of 20 (ZnS):1 (ZnS:Cu):2 (ZnS:Mn) in water. The measured color coordinate of the white light was (0.31, 0.34) in the CIE chromaticity diagram, and the color temperature was 5527 K.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.5
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• pp.437-441
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• 2006

The red emitting OLEDs using $Alq_3$:Rubrene-GDI4234 phosphors have been fabricated and characterized . In the device fabrication, 2- TNATA [4,4',4' - tris (2- naphthylphenyl - phenylamino ) - tripheny lamine] as the hole injection material and NPB [N,N'-bis (1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine] as the hole transport material were deposited on the ITO(indium tin oxide)/glass substrate by vacuum evaporation. And then, red color emissive layer was deposited using $Alq_3$ as the host material and Rubrene(5,6,11,12-tetraphenylnaphthacene)-GDI4234 as the dopants. finally, small molecule OLEDs with structure of ITO/2-TNATA/NPB/$Alq_3$:Rubrene-GDI4234/$Alq_3$/LiF/Al were obtained by in-situ deposition of $Alq_3$, LiF and Al as the electron transport material, electron injection material and cathode, respectively. Red OLEDs fabricated in our experiments showed the color coordinate of CIE(0.65, 0.35) and the maximum power efficiency of 2.1 lm/W at 7 V with the peak emission wavelength of 632 nm.