• Korean Journal of Materials Research
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• v.28 no.8
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• pp.474-477
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• 2018

$Ca_3MgSi_2O_8:Eu^{2+}$(x = 0.003, 0.005, 0.007, 0.01, 0.03 mol) white phosphors for Light Emitting Diodes(LED) are synthesized with different concentrations of $Eu^{2+}$ ions using a solid state reaction method. The crystal structures, surface and optical properties of the phosphors are investigated using X-Ray Diffraction(XRD), Scanning Electron Microscope(SEM) and photoluminescence(PL). The X-Ray Diffraction results reveals that the crystal structure of the $Ca_3MgSi_2O_8:Eu^{2+}$ is a monoclinic system. The particle size of $Ca_3MgSi_2O_8:Eu^{2+}$ white phosphors is about $1{\sim}5{\mu}m$, as confirmed by SEM images. The maximum emission spectra of the phosphors are observed at 0.01 mol $Eu^{2+}$ concentration. The decrease in PL intensity in the $Ca_3MgSi_2O_8:Eu^{2+}$ white phosphors with $Eu^{2+}$ concentration is interpreted by concentration quenching. The International Commission on Illumination(CIE) coordinate of 0.01 mol Eu doped $Ca_3MgSi_2O_8$ is X = 0.2136, Y = 0.3771.

• Korean Journal of Optics and Photonics
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• v.21 no.4
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• pp.139-145
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• 2010

A complete modeling of erbium-doped Bismuth-oxide fibers with a high doping concentration is presented. A 6-level amplifier system that incorporated clustering-induced concentration quenching, cooperative upconversion, pump excited state absorption (ESA), and signal ESA, was adopted for the modeling. The accuracy of the modeling was verified by comparing the calculated gain and noise figure with experimentally obtained ones.

• Journal of the Microelectronics and Packaging Society
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• v.18 no.4
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• pp.79-83
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• 2011

White phosphorescence polymer light emitting diodes (WPhPLEDs) with a glass/ITO/PEDOT:PSS/PFO:$Ir(ppy)_3$:MDMO-PPV/TPBI/LiF/Al structure were fabricated to investigate the effects of $Ir(ppy)_3$ doping concentrations on the optical and electrical properties of the devices. PFO, $Ir(ppy)_3$ and MDMO-PPV conjugated polymers as host and guest materials in the emission layer were spin coated at various concentrations of $Ir(ppy)_3$ ranging from 0.0 to 20.0 vol.%. As the concentration of $Ir(ppy)_3$ increased from 5.0 to 20.0 vol.%, the luminance and current efficiency values of the devices decreased clearly, which are attributable to the quenching effect at a high doping concentration. The maximum luminance and current density were 2850 $cd/m^2$ and 741 $mA/cm^2$, respectively for a WPhPLED with an $Ir(ppy)_3$ concentration of 5.0 vol.%. The CIE color coordinates were about x=0.33 and y=0.34 at 11V, showing a good white color.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.42.2-42.2
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• 2014

We investigate the history of formation of ~400 galaxies in four Abell clusters at 0.04

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.5
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• pp.24-32
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• 2007

Laser surface hardening is beneficially used for surface treatment of structural steel. Due to very rapid heating and cooling rates, structural low-alloy steel(SCM4) can be hardened as self quenching. The aim of this research project is to improve the influence of the process laser parameters: laser power, spot size, surface roughness, and traverse speed. The laser beam is allowed to scan on the surface of the workpiece at the constant power(1095W), varying the traverse speed at 0.3m/min, 0.5m/min and 0.8m/min. The optical lens with the elliptical profile is designed to obtain a wide surface hardening area with uniform hardness. From the results of the experiment, it has been shown that the stable hardness is about 600$\sim$700Hv, when the laser power, focal position and the traverse speed are P=1095W, z=0mm and v=0.3m/min.

• Applied Chemistry for Engineering
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• v.8 no.4
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• pp.637-639
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• 1997

Samples of $YTa_7O_{19}$ doped with $Tm^{3+}$ were prepared using the solid state reaction method to investigate their photoluminescence characteristics. The samples were identified by XRD and SEM, and the optical measurement was also carried out. Under 359 nm excitation, $YTa_7O_{19}$ doped with $Tm^{3+}$ exhibited a narrow-band blue emission, at about 455 nm. The maximum emission intensity was obtained at $YTa_7O_{19}$ doped with 0.12 mole $Tm^{3+}$. This revealed the concentration quenching of emission intensity.

• Korean Journal of Materials Research
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• v.30 no.10
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• pp.515-521
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• 2020

Organic-inorganic hybrid perovskite nanocrystals have attracted a lot of attention owing to their excellent optical properties such as high absorption coefficient, high diffusion length, and photoluminescence quantum yield in optoelectronic applications. Despite the many advantages of optoelectronic materials, understanding on how these materials interact with their environments is still lacking. In this study, the fluorescence properties of methylammonium lead bromide (CH₃NH₃PbBr₃, MAPbBr₃) nanoparticles are investigated for the detection of volatile organic compounds (VOCs) and aliphatic amines (monoethylamine, diethylamine, and trimethylamine). In particular, colloidal MAPbBr₃ nanoparticles demonstrate a high selectivity in response to diethylamine, in which a significant photoluminescence (PL) quenching (~ 100 %) is observed at a concentration of 100 ppm. This selectivity to the aliphatic amines may originate from the relative size of the amine molecules that must be accommodated in the perovskite crystals structure with a narrow range of tolerance factor. Sensitive PL response of MAPbBr₃ nanocrystals suggests a simple and effective strategy for colorimetric and fluorescence sensing of aliphatic amines in organic solution phase.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.107.1-107.1
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• 2012

Because of beautiful glossy and color, the value of gold leverage is very high in Europe. For improve the quality of white gold, we performed heat treatment on 14K white gold alloys at various age-hardening conditions. Age-hardening behavior and the related phase transformation changes were studied to elucidate the hardening mechanism of 14K white gold alloys. For solid solution treatment [ST], casted 14K white gold alloy specimens were treated at high temperature ($750^{\circ}C$) during 30 minute, and the specimens dropped to water for quenching immediately. For Age-hardening treatment [AT], the specimens were treated at various temperatures ($250^{\circ}C{\sim}300^{\circ}C$). After the heat treatment, we observed increased hardness from 144 Hv to 214 Hv by Vicker's hardness tester. Variation of the grain size measured by optical microscopy (OM) and scanning electron microscopy (SEM) images. By electron probe micro-analysis (EPMA) mapping analysis, we investigated that irregular particles were changed uniformly. After heat treatment, 14K white gold alloys showed improved hardness and became uniformity of grain size by age-hardening treatment.

• Journal of the Korean Ceramic Society
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• v.54 no.5
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• pp.422-428
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• 2017

Single-phase yellow phosphor, $CaGd_{2-x}ZrSc(AlO_4)_3:xCe^{3+}$ ($CGZSA:Ce^{3+}$), possessing cubic symmetry with varied $Ce^{3+}$ concentrations, was synthesized using the solid-state reaction method. The samples were characterized using X-ray diffraction (XRD), excitation spectra, emission spectra, thermal quenching, and decay curves. The cubic phase of $CGZSA:Ce^{3+}$ phosphor was confirmed via XRD analysis. The photoluminescence spectra of $CGZSA:Ce^{3+}$ phosphor demonstrated that the phosphor could be excited at the wavelength of 440 nm; a broad yellow emission band was centered at 541 nm. These results indicate that the phosphors are adequately excited by blue light and have the potential to function as yellow-emitting phosphors for applications in white light-emitting diodes.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2005.05a
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• pp.246-251
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• 2005

Laser surface hardening is an effective technique used to improve the tribological properties and also to increase the service life of automobile components such as camshafts, crankshatfs, lorry brake drums and gears. High power $CO_2$ lasers and Nd:YAG lasers are employed for localized hardening of materials and hence are of potential application in the automobile industries. The heat is conducted rapidly into the bulk of the specimen causing self-quenching to occur and the formation of martensitic structure. In this investigation, the microstructure features occurring in Nd:YAG laser hardening SM45C steel are discussed with the use of optical microscopic and scanning electron microscopic analysis. Moreover, This paper describes the optimism of the processing parameters for maximum hardened depth of SM45C steel specimens of 3mm thickness by using CW Nd:YAG laser. Travel speed was varied from 0.6m/min to 1.0m/min. The maximum hardness and case depth fo SM45C steel are 780Hv and 0.4mm by laser hardening.