• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.5
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• pp.437-443
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• 2000

In this study several lanthanide complexes such as Eu(TTA)$_3$(Phen), Tb(ACAC)$_3$-(Cl-Phen) were synthesized and the white-light electroluminescence(EL) characteristics of their thin films were investigated where the devices having structures of anode/TPD/Tb(ACAC)$_3$(Cl-Phen)/Eu(TTA)$_3$(Phen)/Alq$_3$or Bebq$_2$/cathode and the low work function metal alloy such as Li:Al was used as the electron injecting electrode(cathode). Device structure of glass substrate/ITO/TPD(30nm)/Tb(ACAC)$_3$(Phen)(30nm)/Eu(TTA)$_3$(Phen)(6nm)/DCM doped Alq$_3$(10nm)/Alq$_3$(20nm)/Li:Al(100nm) was also fabricated and their EL characteristics were investigated where Eu(TTA)$_3$(Phen) and DCM doped Alq$_3$were used as red light-emitting materials. It was found that the turn-on voltage of the device with non-doped Alq$_3$was lower than that of the devices with doped Alq$_3$and the blue and red light emission peaks due to TPD and Eu(TTA)$_3$(Phen) with non-doped Alq$_3$were lower than those with DCM doped Alq$_3$Details on the white-light-emitting characteristics of these device structures were explained by the energy and diagrams of various materials used in these structure where the energy levels of new materials such as ionization potential(IP) and electron affinity(EA) were measured by cyclic voltametric method.

• Proceedings of the KIEE Conference
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• 1998.11c
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• pp.792-794
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• 1998

The TPD and the $Alq_3$ film are widely used as a hole transport layer and an emitter layer respectively, in organic electroluminescent(EL) device (ITO Glass/TPD/$Alq_3$/metal). In this structure, we fabricated two models. Model(1) having ITO glass/$Alq_3$/Al structure and model(2) having ITO Glass/TPD/$Alq_3$/Al structure were fabricated by the vacuum evaporation. The comparison between model(1) and model(2) was made about the absorbance, the wave length, the current-voltage characteristic and the ln I - $V^{(1/2)}$characteristic respectively. Electroluminescence of green and wavelength of 510[nm] were observed in both model. We observed absorbance from 320[nm] to 430[nm] in $Alq_3$ material and from 250[nm] to 400[nm] in TPD material.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.11a
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• pp.578-580
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• 2002

A bright and highly monochromatic red organic electroluminescent device based on a poly(N-vinylcarbazole) host was made. The device structure consists of poly(N-vinylcarbazole) dispersed with a europium complex as an emitting layer and a hole blocking layer of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP). The EL cell exhibited just characteristic emission of europium ion.

• Journal of the Korean Vacuum Society
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• v.18 no.1
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• pp.37-43
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• 2009

Temperature and injection current dependence of electroluminescence(EL) spectral intensity of the $In_xGa_{1-x}N$/GaN multi-quantum wells(MQW) have been studied over a wide temperature range and as a function of injection current level. It is found that a temperature-dependent variation pattern of the EL efficiency under very low and high injection currents shows a drastic difference. This unique EL efficiency variation pattern with temperature and current can be explained field effects due to the driving forward bias in presence of internal(piezo and spontaneous polarization) fields. Increase of the indium content in $In_xGa_{1-x}N$/GaN multiple quantum wells gives rise to a redshift of 80 meV and 22 meV for green and blue MQW, respectively. It can be explained by carrier localization by potential fluctuation of multiple quantum well and MQW structures also shows a keen difference owing to the different indium content in InGaN/GaN MQW.

• Polymer(Korea)
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• v.25 no.3
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• pp.399-405
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• 2001

Poly[3-octylthiophene-co-3-(4-fluorophenyl)thiophene]s were synthesized in 2:1, 1:1, and 1:2 mole ratios, and organic electroluminescent devices were fabricated using the copolymers. The opto-electrical properties of the copolymers were studied by PL, EL spectra, I-V, and V-L curves of the organic electroluminescent devices in conjunction with the energy band diagrams which were obtained from the cyclic voltammogram and the electronic absorption spectra. The LUMO energy level of P(OT/FPT)(1:1) is the lowest as -3.35 eV. In the copolymers P(OT/FPT)(2:1) and P(OT/FPT)(1:1) the ${\lambada}_{max}$ in the PL and EL spectra red-shifted as the mole ratio of fluorophenyl group increased while in P(OT/FPT)(1:2) it showed a blue-shift. This indicates that the backbone chain is twisted due to the steric hinderance of the fluorophenyl group leading to shorter ${\pi}$-conjugation length. P(OT/FPT)(1:1) showed the highest EL intensity and the highest power efficiency among the three copolymers. In P(OT/FPT)(1:2) the roughness of the film surface causes unusually high local leakage current leading to the low efficiency of electroluminescence.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.5
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• pp.285-295
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• 1999

Electroluminescent(EL) devices based on organic materials have been of great interest due to their possible applications for large-area flat-panel displays. They are attractive because of their capability of multi-color emission, and low operation voltage. An approach to realize such device characteristics is to use active layers of lanthanide complexes with their inherent extremely sharp emission bands in stead of commonly known organic dyes. In general, organic molecular compounds show emission due to their $\pi$-$\pi*$ transitions resulting in luminescence bandwidths of about 80 to 100nm. Spin statistic estimations lead to an internal quantum efficiency of dye-based EL devices limited to 25%. On the contrary, the fluorescence of lanthanide complexes is based on an intramolecular energy transfer from the triplet of the organic ligand to the 4f energy states of the ion. Therefore, theoretical internal quantum efficiency is principally not limited. In this study, Powders of TPD, $Eu(TTA)_3(phen) and AlQ_3$ in a boat were subsequently heated to their sublimation temperatures to obtain the growth rates of 0.2~0.3nm/s. Organic electrolumnescent devices(OELD) with a structure of $glass substrate/ITO/Eu(TTA)_3(phen)/AI, glass substrate/ITO/TPD/Eu(TTA)_3(phen)/AI and glass substrate/ITO/TPD/Eu(TTA)_3(phen)/AIQ_3AI$ structures were fabricated by vacuum evaporation method, where aromatic diamine(TPD) was used as a hole transporting material, $Eu(TTA)_3(phen)$ as an emitting material, and Tris(8-hydroxyquinoline)Aluminum$(AlQ_3)$ as an electron transporting layer. Electroluminescent(EL) and current density-voltage(J-V) characteristics of these OELDs with various thickness of $Eu(TTA)_3(phen)$ layer were investigated. The triple-layer structure devices show the red EL spectrum at the wavelength of 613nm, which is almost the same as the photoluminescent(PL) spectrum of $Eu(TTA)_3(phen)$.It was found from the J-V characteristics of these devices that the current density is not dependent on the applied field, but on the electric field.

• Journal of the Korean Ceramic Society
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• v.41 no.5
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• pp.406-409
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• 2004

A blue phosphor(ZnS:Cu) is manufactured by solid state reaction for ACPEL(AC powder EL). The effect of artificial defect on phosphor surface on the ZnO phase conversion and resulting luminescence have been studied. It was found that ZnS:Cu could converse to cubic phase more easily due to the formation of artificial defect on 1st fired phosphor by ball-milling process, resulting in improvement of luminescence of phosphor phosphors under the driven EL condition. We found out an optimized ball-mill condition through considering effect of each ball-mill conditions such as milling time and milling rpm on defect. Also we determined relationship between emission luminescence and phase of phosphor based on analyses of crystal structures of phosphors. A significant improvement above 30% was observed in electroluminescence by the artificial defect on ZnS:Cu phosphors compared to non-treated phosphors.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1404-1407
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• 2005

We have fabricated organic light-emitting diodes using poly(N-vinylcarbazole)(PVK) doped with N,N'- diphenyl-N,N'-bis(3-methylphenyl)-[l,l'-biphenyl]- 4,4/-diamine (TPD) as the hole transport layer. TPD molecules act as the trapping sites in PVK and reduce the hole mobility, which can enhance the electronhole balance in the emitting layer, resulting in the enhanced device performance. We have found the optimum ratio of TPD to PVK for the EL efficiency.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.621-624
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• 2007

As a new fluoranthene derivative, a synthesis of benzo[k]fluoranthene was suggested, so new blue emitting materials, 7,12-diphenylbenzo[k] fluoranthene [DPBF] and 7,8,10- triphenylfluoranthene [TPF] were synthesized. $EL_{max}$ wavelength of the device using DPBF as an emitting layer was 436 and 454nm in the deepblue region, which are similar values with PL. The device that used DPBF as an emitting layer showed high efficiency of 2.11cd/A and the excellent color coordinate value of (0.161, 0.131) in deep-blue region.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.4
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• pp.514-519
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• 2006

SrS:Cu, Cl thin films have been grown by the hot wall technique with S furnace placed on the outside of the growth chamber in order to investigate the crystallographic and optical characteristics. The films have a good crystallinity independent of CuCl wall temperature and PL characteristics showed a peak assigned by the transition form $3d^94s^1\;(^3Eg)$ to $3d^{10}\;(^1A_{1g})$ of $Cu^+$ center. It has also been found that. from the PLE spectra, $Cu^+$ luminescent centers are doped in the host materials. The EL emission from SrS:Cu-based device showed a greenish-blue but shifted to short wavelength compared to SrS:Ce-based EL. The device was obtained the maximum luminance of $110cd/m^2$ and the maximum luminous efficiency of $0.1\;lm/W$ at $V_{40}$.