• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.51-52
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• 2007

Built-in voltage in organic light-emitting diodes was studied using modulated photocurrent technique ambient conditions. From the bias voltage-dependent photocurrent, built-in voltage of the device is determined. The applied bias voltage when the magnitude of modulated photo current is zero corresponds to a built-in voltage. Built-in voltage in the device is generated due to a difference of work function of the anode and cathode. A device was made with a structure of anode/$Alq_3$/cathode to study a built-in voltage. ITO and ITO/PEDOT:PSS were used as an anode, and Al and LiF/AI were used as a cathode. It was found that an incorporation of PEDOT:PSS layer between the ITO and $Alq_3$ increases a built-in voltage by about 0.4V. This is consistent to a difference of a highest occupied energy states of ITO and PEDOT:PSS. This implies that a use of PEDOT:PSS layer in anode improves the efficiency of the device because of a lowering of anode barrier height. With a use bilayer cathode system LiF/Al, it was found that the built-in voltage increases as the LiF layer thickness increases in the thickness range of 0~1nm. For 1nm thick LiF layer, there is a lowering of electron barrier by about 0.2eV with respect to an Al-only device. It indicates that a very thin alkaline metal compound LiF lowers an electron barrier height.

• Bulletin of the Korean Chemical Society
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• v.32 no.5
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• pp.1583-1586
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• 2011

Silver nanoparticles (<10 nm) were prepared in ultrasonic vibration-induced nanodroplets of isopropyl alcohol (IPA) in combination with hydrophobic room temperature ionic liquids (RTILs). The Ag-precursor used were silver (I) complex, Ag$_2$(ehac)$_2$(eha)$_2$ (ehac = 2-ethylhexylammonium carbamate; eha = 2-ethylhexylamine), in IPA, while 1-butyl-3-methylimidazolium-based ionic liquids bearing $SbF_6^-$, $PF_6^-$ and $NTf_2^-$ as counter anions were used as RTILs. During sonication for 10-90 min at room temperature, uniform silver nanoparticles with mean sizes of 2 to 8 nm were rapidly synthesized. Transmission electron micrographs also confirmed that silver nanoparticles have a spherical shape and diverse sizes depending on the reaction time (10-90 min).

• Korean Journal of Materials Research
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• v.26 no.9
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• pp.504-511
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• 2016

To prepare $Mn^{4+}$-activated $K_2TiF_6$ phosphor, a precipitation method without using hydrofluoric acid (HF) was designed. In the synthetic reaction, to prevent the decomposition of $K_2MnF_6$, which is used as a source of $Mn^{4+}$ activator, $NH_5F_2$ solution was adopted in place of the HF solution. Single phase $K_2TiF_6$:$Mn^{4+}$ phosphors were successfully synthesized through the designed reaction at room temperature. To acquire high luminance of the phosphor, the reaction conditions such as the type and concentration of the reactants were optimized. Also, the optimum content of $Mn^{4+}$ activator was evaluator based on the emission intensity. Photoluminescence properties such as excitation and emission spectrum, decay curve, and temperature dependence of PL intensity were investigated. In order to examine the applicability of this material to a white LED, the electroluminescence property of a pc-WLED fabricated by combining the $K_2TiF_6$:$Mn^{4+}$ phosphor with a 450 nm blue-LED chip was measured.

• Korean Journal of Materials Research
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• v.32 no.9
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• pp.379-383
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• 2022

In this study, Barium Germanium glasses were prepared with a composition of xBaO-(72-x)GeO₂-8La₂O₃-20ZnO where x = 16.0, 18.0, 20.0, 22.0 and 24.0 mol% respectively. Their physical and optical properties, such as refractiveness index, glass transition temperature (T_g), softening temperature (T_s), transmittance and Knoop hardness were studied. The results showed that refractive index, T_g, T_s and coefficient of thermal expansion (CTE) increased with increasing BaO concentration. The refractive index of all the prepared samples was observed between 1.7811 to 1.7881. The Abbe number was calculated by formula using n_d (589.3 nm), n_f (656.3 nm) and n_c (486.1 nm) and observed to be between 38 to 40. The Abbe number of the prepared sample was similar to that of BaO and GeO₂. The transmittance of the prepared glasses was observed to be between 80 ~ 82 % throughout the range from 200 nm to 800 nm. Knoop hardness divided into seven steps were measured 5 class (≥ 450 ~ < 550) of all prepared samples.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.257-259
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• 2002

As a new host material for a red phosphor for PDP applications, has studied (Y,Gd)$Al_3(BO_3)_4$ which gives non-centrosymmetric sites for $Eu^{3+}$ activators. Vacuum ultraviolet (VUV) excitation spectrum of new red phosphor (Y,Gd)$Al_3(BO_3)_4$:$Eu^{3+}$ has two broad bands. One band with the absorption edge at ca. 168 nm is the band-gap absorption of aluminoborate and the other broad band centered 240 nm is the charge transfer transition between $Eu^{3+}$ and the neighboring oxygen anions. The PL spectrum shows the strongest emission at 617 nm due to the electric dipole $^5D_0{\rightarrow}^7F_2$ transition of $Eu^{3+}$, whose luminescent chromaticity is (0.67, 0.33).

• 한국연소학회:학술대회논문집
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• 2004.06a
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• pp.27-33
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• 2004

The Noise generation mechanisms of propane laminar premixed flames on a slot burner have been studied experimentally. The sound levels and frequencies were measured for various mixture flow rates (velocities) and equivalence ratios. The primary frequency of self-induced noise increases with the mean velocity of mixture as $f{\;}{\propto}{\;}U_f^{1.144}$ and the measured noise level increases with the mixture flow rate and equivalence ratio as $p{\;}{\propto}{\;}U_f^{1.7}$$F^{8.2}$. The nature of flame oscillation and the noise generation mechanisms are also investigated using a high speed CCD camera and a DSRL camera. The repetition of sudden extinction at the tip of flame is evident and the repetition rates are identical to the primary frequencies obtained from the FFT analysis of sound pressure signals. CH chemiluminescence intensities of the oscillating flames were also measured by PMT with a 431 nm(10 FWHM) band pass filter and compared to the pressure signals.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08b
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• pp.1703-1705
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• 2007

Before the ultra-violet glue encapsulation, the research evaporated LiF thin film on device surface to be the extra packaging layer for improving the lifetime of organic light-emitting diode. The formula of UV glue was specially developed. We found 100 nm LiF is the optimum thickness. The best lifetime obtained by using LiF and special UV glue is 2.4 times longer than those by commercial UV glue.

• Journal of the Korean Electrochemical Society
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• v.12 no.3
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• pp.234-238
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• 2009

In the excitation spectra of $YNbO_4$ : $Eu^{3+}$, the charge transfer (CT) band around 270 nm due to $[NbO_4]^{3-}$$-Eu^{3+}$ interaction and sharp excitation peaks by f-f transition of $Eu^{3+}$ strongly appeared simultaneously. CT band depended on the structural properties of powders, showing the red-shift with increasing the crystallinity, while the f-f transition peaks were independent of the crystallinity. For $YNb_{1-x}Ta_xO_4$ : $Eu^{3+}$ (x = 0.05.0.2), $[TaO_4]^{3-}$. configuration was locally constructed, leading to the blue-shift in CT band and the decrease in the red emission intensity with increasing the Ta content.

• Bulletin of the Korean Chemical Society
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• v.28 no.12
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• pp.2477-2480
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• 2007

MgAl2O4:Eu3+ red-light emitting powder phosphor was prepared at temperature as low as 500 oC within a few minutes by using the combustion route. The prepared powder was characterized by X-ray diffraction, scanning electron microscopy and Fourier-transform infrared spectrometry. The luminescence of Eu3+-activated MgAl2O4 shows a strong red emission dominant peak around 611 nm, which can be attributed to the 5D0-7F2 transition of Eu3+ ions from the synthesized phosphor particles under excitation (394 nm). Electron paramagnetic resonance (EPR) measurements at the X-band showed that no signal could be attributed to Eu2+ ions in MgAl2O4.

• Carbon letters
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• v.6 no.2
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• pp.86-88
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• 2005

Mesoporous activated carbon (AC) was prepared from aged petroleum coke through chemical activation. The AC has a specific surface area of 1733 $m^2/g$ and a mean pore diameter of 2.37 nm. The volume fraction of 2 to 4nm pores is 56.74%. At a current density of 10 mA/$cm^2$, a specific capacitance of 240 F/g is achieved representing the use factor of the surface area of 69.2%. And the electrical double layer capacitor (EDLC) based on the AC shows an excellent power performance. This result suggests that the presence of high fraction of mesopores can effectively increase the adsorption efficiency of the specific surface area of the AC and enhance the power performance of EDLC based on the efficient surface area of the AC.