• Bulletin of the Korean Chemical Society
• /
• v.31 no.12
• /
• pp.3711-3717
• /
• 2010

Four orange-red phosphorescent Ir(III) complexes were designed and synthesized based on the benzoylphenylpyridine ligand with a fluorine substituent. Multilayered OLEDs with the device structure, ITO/2-TNATA/NPB/CBP : 8% Ir(III) complexes/BCP/Liq/Al, were fabricated using these complexes as dopant materials. All the devices exhibited orange-red electroluminescence and their electroluminescent properties were quite sensitive to the structural features of the dopants in the emitting layers. Among these, the maximum luminance ($14700\;cd/m^2$ at 14.0 V) was observed in the device containing Ir(III) complex 1 as the dopant. In addition, its luminous, power and quantum efficiency were 11.7 cd/A, 3.88 lm/W and 9.58% at $20\;mA/cm^2$, respectively. The peak wavelength of electroluminescence was 606 nm with CIE coordinates of (0.61, 0.38) at 12.0 V. The device also showed stable color chromaticity with various voltages.

• Journal of the Korean Society for Precision Engineering
• /
• v.29 no.7
• /
• pp.778-784
• /
• 2012

In comparison with some other light sources, LED has merits such as increased life expectancy, fast response, pollution free, and high energy efficiency. Lately, due to development of LED with high brightness and capacity, LED has widely used in many industrial fields such as automotive, aviation, display, transportation and special lighting applications. Since the high heat generation of LED chips can cause a reduction in lifetime, degradation of luminous efficiency, and variation of color temperature, studies have been carried out on the optimization of LED packaging and heat sinks. In this study, experiments on measuring the heat generation rate of LED and the cooling performance of a heat sink were carried for analyzing the thermal characteristics of LED lighting system in free convection. From the results, dimensionless correlation on the cooling performance of heat sink in natural convection was proposed with Nusselt number and Rayleigh number as a guideline for designing cooling device of LED lightings.

• Korean Journal of Optics and Photonics
• /
• v.25 no.4
• /
• pp.216-220
• /
• 2014

We have synthesized a $CaMgSi_2O_6:Eu^{2+}$ blue phosphor via a solid-state reaction method. The $CaMgSi_2O_6:Eu^{2+}$ phosphor has monoclinic structure with a space group of C2/c (15), and an emission band peaking at 450 nm (blue) due to the $4f^7-4f^65d$ transition of the $Eu^{2+}ion$. The emission intensity at $100^{\circ}C$ is 54% of the value at room temperature. A white LED was fabricated by integrating a UV LED (400 nm) with our blue phosphor plus two commercial green and red phosphors. The white LED shows a color temperature of 3500 K with a color rendering index of 87 (x = 0.3936, y = 0.3605), and a luminous efficiency of 18 lm/W. The white LED shows a luminance maintenance of 97% after operation at 350 mA for 400 hours at $85^{\circ}C$.

• Proceedings of the Safety Management and Science Conference
• /
• 2010.11a
• /
• pp.63-80
• /
• 2010

This paper describes the development of various lighting equipment adapting Ultra Constant Discharge Lamp that has newly been on commercial supply in the market. Meeting the required conditions of lighting equipment, various types of UCD Lamp equipment with excellent performances could be successfully developed. In order to provide a guideline for the economical lighting product selection, the analyzed data comparison between Hi-pressure Sodium Lamp which has been the most popular lamp for street lighting and UCD Lamp is provided. The conclusions of the study are made as follows; (1) The performance measurement result of UCD Lamp shows excellent Luminous Efficacy as 108Lm/W, daylight-like Color Rendering Index as 90Ra, and the best operating temperature range as $-50^{\circ}C{\sim}+85^{\circ}C$. Comparing to the Hi-pressure Sodium Lamp, UCD could be evaluated as much superior products. (2) In an assembled status with the lighting fixture (Type STB형-60W), UCD Lamp was tested OK for one hour duration at the temperature range form $-50^{\circ}C$ to $+85^{\circ}C$ and the humidity of 98%. The operation at the extremely low temperature can be an excellent feature to enable the export to the cold temperature regions such as Northern Europe and Russia and the specific applications for defense systems and special industry. (3) As UCD Lamp is a genuine Korea made product following Energy-saving and Eco-friendly policy, it should be appreciated as one of the best $CO^2$ reduction Green product.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.30 no.2
• /
• pp.73-77
• /
• 2020

In this study, phosphor ceramics were fabricated, and optical properties were analyzed for application to nextgeneration automotive laser headlamps by using a spherical YAG : Ce phosphor with a garnet structure synthesized based on the spray drying method. The thickness of phosphor ceramic using spherical YAG : Ce phosphor was obtained with 100 ㎛, 150 ㎛, and 200 ㎛ to investigate the effect of thickness on optical properties such as light conversion efficiency, heat dissipation, luminance and color temperature. The results of this study are expected to play a significant role in the manufacturing process for the fabrication of phosphor ceramic by solving issues such as the high cost and low yield in the conventional liquid method to manufacture YAG : Ce nano fluorescent materials.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.30 no.9
• /
• pp.577-582
• /
• 2017

The white light of a hybrid LED is obtained by using red and green organic fluorescent layers made of polymethylmethacrylate (PMMA) films, which function as color down-conversion layers of blue light-emitting diodes. In this research, we studied the fluorescence properties of a red organic fluorophore, employing perylene bisimide derivatives applicable to hybrid LEDs. The solubility, thermal stability, and luminous efficiency are important characteristics of organic fluorophores for use in hybrid LEDs. The perylene fluorescent compounds (1A and 1B) were prepared by the reaction of 4-bromophenol and 4-iodophenol with N,N'-bis(4-bromo-2,6-diisopropylphenyl)-1, 6,7,12-tetrachloroperylene-3,4,9,10-tetracarboxyl diimide (1) in the presence of dimethyl formaldehyde (DMF) at $70^{\circ}C$. The synthesized derivatives were characterized by using $^1H-NMR$, FT-IR, UV/Vis absorption and PL spectra, and TGA analysis. Compounds 1A and 1B showed absorption and emission at 570 nm and 604 nm in the UV/Vis spectrum. We also documented favorable solubility and thermal stability characteristics of the perylene fluorophores in our work. Perylene fluorophore 1, with the 4-bromophenol substituent 1A, exhibited particularly good thermal stability and solubility in organic solvents.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.19 no.1
• /
• pp.24-33
• /
• 2005

This paper presents dimming control system for automotive 35[W] metal halide discharge(MHD) lamp electronic ballast using digital control method. HID system has been becoming increasingly popular due to its superior performance(high luminous efficacy, good color rendering and long life etc.)over the conventional halogen system. However, this lamp demands a highly efficient ballast and very complex control circuitry that can control complex transient state in applying to automotive. Therefore, in this paper, digital control method for the HID lamp ballast is presented for optimal control that can adapt complex transient state, steady state and various environments. In developed dimming system, the system is designed to control the lamp output voltage step by step using microcontroller according to cds sensor. Therefore the designed dimming control system give good driving condition to diver and realize the power control effectively. The results of the proposed system is verified through various simulation results and the experiment results.

• Journal of the Korea Safety Management & Science
• /
• v.12 no.4
• /
• pp.41-51
• /
• 2010

This paper describes the development of various lighting equipment adapting Ultra Constant Discharge Lamp that has newly been on commercial supply in the market. Meeting the required conditions of lighting equipment, various types of UCD Lamp equipment with excellent performances could be successfully developed. In order to provide a guideline for the economical lighting product selection, the analyzed data comparison between Hi-pressure Sodium Lamp which has been the most popular lamp for street lighting and UCD Lamp is provided. The conclusions of the study are made as follows; (1) The performance measurement result of UCD Lamp shows excellent Luminous Efficacy as 108Lm/W, daylight-like Color Rendering Index as 90Ra, and the best operating temperature range as $-50^{\circ}C{\sim}+85^{\circ}C$. Comparing to the Hi-pressure Sodium Lamp, UCD could be evaluated as much superior products. (2) In an assembled status with the lighting fixture (Type STB형-60W), UCD Lamp was tested OK for one hour duration at the temperature range form $-50^{\circ}C$ to $+85^{\circ}C$ and the humidity of 98%. The operation at the extremely low temperature can be an excellent feature to enable the export to the cold temperature regions such as Northern Europe and Russia and the specific applications for defense systems and special industry. (3) As UCD Lamp is a genuine Korea made product following Energy-saving and Eco-friendly policy, it should be appreciated as one of the best $CO^2$ reduction Green product.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.25 no.2
• /
• pp.124-131
• /
• 2016

Several research works for finding and optimizing the methods of dispensing high viscosity phosphor used in the fabrication of white LED's are currently in progress. High viscosity phosphor dispensing with a high accuracy is crucial because the dispensing rate and uniformity directly affect parameters such as the CIE chromaticity diagram, color temperature and luminous flux of white LED's. This study presents a novel method of dispensing high viscosity phosphor using electrohydrodynamic printing. The dispensing rate was optimized less than 0.01 mg phosphor using experiments and optimizing the process parameters including the standoff distance from the nozzle to the substrate, ink supply pressure, and multi-step pulsed waveform magnitude ratio. The dispensing rate was measured by dispensing 20 dots using drop-on-demand with the optimized parameters, and the experiments were repeated 10 times to maximize the data accuracy. The average dispensing rate that can be reliably used for high viscosity phosphor dispensing was 0.0052 mg.

• Restorative Dentistry and Endodontics
• /
• v.49 no.3
• /
• pp.27.1-27.13
• /
• 2024

Objectives: This study aimed to develop whitening mouth rinses formulated with industrial mushrooms and compare them with over-the-counter whitening mouth rinses. Materials and Methods: Formulations with black shimeji mushrooms, mushroom substrates, and mushroom stalks were developed. Bovine enamel/dentin samples were divided into 7 groups (n = 10): Colgate Luminous White, Listerine Whitening Extreme (LWE), Listerine Cool Mint (LC), mushroom extract rinse (MEC), mushroom substrate rinse (MSB), mushroom stalk rinse (MTC), and artificial saliva. Samples were stained with black tea for 6 days, and then were immersed in 100 mL of each mouth rinse twice daily for 14 days. Color parameters (CIELAB [ΔE^*], CIEDE2000 [ΔE₀₀], whiteness index for dentistry [ΔWI_D]) and microhardness (Knoop hardness number [KHN]) were analyzed at T₁ (initial), T₂ (24 hours), and T₃ (7 days). Mouth rinse pH was measured, and enamel was examined using a scanning electron microscope. Data were analyzed using generalized linear models, and KHN with the generalized linear mixed model for repeated measures (p ≤ 0.05). Results: ΔE^* was higher in LW and MSB groups. No significant differences were found for ΔE₀₀ (p = 0.0982) and ΔWI_D (p = 0.2536). Experimental mouth rinses did not promote enamel whitening based on ΔE₀₀ and ΔWI_D. LWE and LC reduced KHN and had a more acidic pH, while MEC had higher KHN at T2. MEC, MSB, and MTC had alkaline pH, not altering the tooth surface. Conclusions: Black shimeji mushrooms are promising for mouth rinse development due to their alkaline pH and non-altering effect on surface microhardness.