• Journal of Information Display
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• v.13 no.1
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• pp.37-42
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• 2012

An empirical functional form was suggested for the analysis of the emission spectrum of high-power light-emitting diode (LED) consisting of a sharp blue peak from the LED chips and a broad yellow peak from the phosphor layer. The peak positions, half widths, shape parameters, and amplitudes of these two peaks were reliably obtained as a function of the temperature, and the results were discussed qualitatively in relation with the junction temperature. The adoption of an inert liquid was found to have significantly reduced the LED temperature and the color shift of the emitted light. The phenomenological approach used in this study may be helpful in the simulation of the LED spectrum under various thermal conditions, and may thus be helpful in the improvement of the device performance.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.431-434
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• 2007

Rapid progress has been made in the development of commercially viable Light Emitting Polymer (LEP) materials for display and lighting applications. This presentation will focus on: ${\bullet}$ Degradation studies that have led to the design of new and improved materials ${\bullet}$ Recent lifetime and efficiency results for red, green, blue, and white polymers ${\bullet}$ Challenges of formulating inks that can be used in a production environment

• Journal of the Semiconductor & Display Technology
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• v.18 no.4
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• pp.51-56
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• 2019

LuAG:Ce(Lu₃Al₅O₁₂:Ce³⁺) nano phosphor were synthesized by applying the coprecipitation method. It is used to increase the color rendering of phosphor ceramic plate for high power LEDs and laser lighting. Internal quantum efficiency and absorption of LuAG:Ce nano phosphor are 51.5 % and 64.4 %, respectively, which is higher than the previously studied nano phosphors. The maximum absorption wavelength of this phosphor is 450 nm blue light, and the emission wavelength is 510 nm. The emission wavelength shifted to longer wavelength when the concentration of Ce increased in the heat treatment of the reducing atmosphere. Thermal quenching of LuAG nano phosphor was 70 % at 200 ℃, it was explained by their significant quenching of all raman scattering modes, implying the restriction of electron-phonon couplings caused by their defects.

• Korean Journal of Social Welfare
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• v.57 no.2
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• pp.93-118
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• 2005

This research examined influence of job stress and drinking subculture on the drinking of white collar employees. The results are as follows: First, there are a higher percentage of population among white collar employees who hold drinking problems in terms of frequency of drinking, amount of drinking, frequency of binge drinking comparing with general populace. The results of research revealed that drinking problems of white collar employees is quite close to dangerous level. Second, job stress didn't display a consistent relationship with drinking and drinking problem, however, drinking subculture revealed that it was related with drinking and drinking problem exhibiting significant influence. And, the results of research didn't support tension reduction hypothesis, and it was identified that social learning theory is main factor that will explain drinking and drinking problem of white collar employees. Therefore, researcher suggested as follow; First, practitioners and researchers exert their efforts for studying about drinking in the relationship to white collar employees. They should also have more interests in the topic from a practical perspective. Second, suggest that EAPs be introduced in order to prevent white collar employees from drinking problem and to promote increase of entire welfare. Third, suggest that succeeding research endeavors be required, which shall embrace all of white & blue collar employees.

• 한국정보디스플레이학회:학술대회논문집
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• 2003.07a
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• pp.940-943
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• 2003

We report the fabrication and the characterization of white organic light-emitting devices consisting of a red-emitting layer of a new DCM derivative doped into 4,4'bis[N-(1-napthyl)-N-phenyl-amino]-biphenyl (${\alpha}-NPD$) and a blue-emitting layer of 1,4-bis(2,2-diphenyl vinyl)benzene (DPVBi). The device structure is ITO/PEDOT:PSS/${\alpha}-NPD$ (50 nm)/${\alpha}-NPD$:DCM (5 nm, 0.2 %)/DPVBi (x)/Alq3 (40 nm)/LiF (0.5 nm)/Al. The electroluminescence (EL) spectra consist of two broad peaks around 470 nm and 580 nm with the spectral emission depending on the thickness of DPVBi. The device with the DPVBi thickness of about 20 nm show a white light-emission with the Commission Internationale d'Eclairage(CIE) chromaticity coordinates of (0.33, 0.36). The external quantum efficiency is 2.6% and luminous efficiency is 2.0 lm/W at a luminance of 100 $cd/m^{2}$. The maximum luminance is about 30,270 $cd/m^{2}$ at 13.9 V.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.780-783
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• 2002

We report very efficient white OLEDs consisting of a blue-emitting 4,4'bis[N-(1-napthyl)-N-phenyl-amino]-biphenyl (${\alpha}$-NPD), a hole-blocking layer of 2,9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline (BCP) doped with red fluorescent dye of 4-dicyanomethylene-2-methyl-6-[2-(2,3,6,7-tetrahydro- 1H, 5H-benzo[i,j]quinolizin-8-yl) vinyl]-4H-pyran) (DCM2), and green-emitting tris(8-hydroxyquinoline) aluminum ($Alq_3$). The device with the structure of ITO/${\alpha}$-NPD (50 nm)/BCP:DCM2 (0.8 %, 4 nm)/$Alq_3$ (50 nm)/LiF (0.5 nm)/Al shows a white emission with the CIE coordinates (0.329, 0.333). The maximum luminance of 20,800 cd/$m^2$ is obtained at 15.4 V. The power efficiency is 2.6lm/W and the external quantum efficiency is 2.1 % at a luminance of 100 cd/$m^2$ at the bias voltage of 6 V.

• Korean Journal of Optics and Photonics
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• v.35 no.3
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• pp.95-106
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• 2024

In the 21st century, white light-emitting diodes (LEDs) are widely used as backlighting for liquid crystal displays and as a light source for general illumination. However, white LEDs used in lighting often use a single yellow phosphor on top of a blue LED chip, which lacks the ability to reproduce natural colors in objects under conventional illumination accurately. Recently, researchers have been actively working on realizing high color-rendering lighting by incorporating red quantum dots to improve the spectrum in the long-wavelength band, which is deficient in conventional white LEDs. In particular, how to develop and apply remote quantum dot components to ensure long-term reliability is currently under active research. This paper introduces recent research on remote quantum dot components and the current status of developing high color-rendering lightings with them. Especially, we focus on various factors that are important to consider in optimizing the optical structure of the quantum dot components and discuss the future directions and prospects of research for high color-rendering lighting technology.

• Current Optics and Photonics
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• v.4 no.3
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• pp.221-228
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• 2020

We developed an all-fiber RGB laser light source module for application in an automobile head-up display. It is based on laser diodes and an optical fiber combiner that substantially enhances the flexibility of configuration and stability against harsh working conditions for automobiles. We coupled 13 laser diodes with optical fibers and merged them into a single output with a beam combiner device. Red (R), green (G), and blue (B) laser sources were employed to produce primary colors that were mixed into a white light output. An optical output power of approximately 1.5 W was achieved, and the color balance of the output lights was assessed based on the CIE 1931 color space. The optical output power was shown to be stable for over 160 h within an optical fluctuation of less than 0.27%.

• Korean Journal of Materials Research
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• v.29 no.2
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• pp.116-120
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• 2019

We prepared $Y_3Al_5O_{12};Ce^{3+},Pr3^{+}$ transparent ceramic phosphor using a solid state reaction method. By XRD pattern analysis and SEM measurement, our phosphors reveal an Ia-3d(230) space group of cubic structure, and the transparent ceramic phosphor has a polycrystal state with some internal cracks and pores. In the Raman scattering measurement with an increasing temperature, lattice vibrations of the transparent ceramic phosphor decrease due to its more perfect crystal structure and symmetry. Thus, low phonon generation is possible at high temperature. Optical properties of the transparent ceramic phosphor have broader excitation spectra due to a large internal reflection. There is a wide emission band from the green to yellow region, and the red color emission between 610 nm and 640 nm is also observed. The red-yellow phosphor optical characteristics enable a high Color Rendering Index (CRI) in combination with blue emitting LED or LD. Due to its good thermal properties of low phonon generation at high temperature and a wide emission range for high CRI characteristics, the transparent ceramic phosphor is shown to be a good candidate for high power solid state white lighting.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.688-691
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• 2004

In this study, we synthesized a new red emitting material of a Red225 doped into $Alq_3$ (tris(8-quinolinolato)aluminum (III)) and fabricated white organic light-emitting diodes (OLEDs) with a simple device structure. With a blue emitting material of DPVBi (4,4'-bis(2,2'-diphenylvinyl)1,1'-biphenyl) that can transfer effectively both a hole and an electron, OLEDs with a narrow emission layer could be possible without a hole-blocking layer. Consequently, the driving voltage and stability of devices have been improved. The devices show the Commission Internationale d'Eclairage (CIE) chromaticity coordinates of (0.36, 0.35) at luminance of 2000 cd/$m^2$. The luminous efficiency is about 3.5 cd/A, luminance is about 12000 cd/$m^2$ and current density is about 350 mA/$cm^2$ at 12 V, respectively.