• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.531-531
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• 2012

So many groups have been researching the green quantum dots such as InP, InP/ZnS for overcoming the semiconductor nanoparticles composed with heavy metals like as Cd and Pb so on. In spite of much effort to keep up CdSe quantum dots, it does not reach the good properties compared with CdSe/ZnS quantum dots. This quantum dot has improved its properties through the generation of core/shell CdSe/ZnS structure or core/multi-shell structures like as CdSe/CdS/ZnS and CdSe/CdS/ CdZnS/ZnS. In this research, we try to synthesize the InP multi-shell structure by the successiveion layer absorption reaction (SILAR) in the one pot. The synthesized multi-shell structure has improved quantum yield and photo-stability. To generate white light, highly luminescent InP multi-shell quantum dots were mixed with yellow phosphor and integrated on the blue LED chip. This InP multi-shell improved red region of the LEDs and generated high CRI.

• Journal of Powder Materials
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• v.29 no.6
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• pp.453-458
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• 2022

We successfully synthesize water-dispersible CTAB-capped CdSe@ZnS quantum dots with the crystal size of the CdSe quantum dots controlled from green to orange colors. The quenching effect of Fe(DTC)₃ is very efficient to turn off the emission light of quantum dots at four molar ratios of the CdSe quantum dots, that is, the effective covering the surface of quantum dots with Fe(DTC)₃. However, the reaction with Fe(DTC)₃ for more than 24 h is required to completely realize the quenching effect. The highly quenched quantum dots efficiently detect nitric oxide at nano-molar concentration of 110nM of NO with 34% of recovery of emission light intensity. We suggest that Fe(DTC)₃-hybridized CdSe@ZnS quantum dots are an excellent fluorescence resonance energy transfer probe for the detection of nitric oxide in biological systems.

• Journal of the Semiconductor & Display Technology
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• v.20 no.3
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• pp.11-17
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• 2021

I performed a semi-analytical numerical analysis of the effects of core size and electric field intensity on the light emission wavelength of CdSe/ZnS quantum dots (QDs). The analysis used a quantum mechanical approach; I solved the Schrödinger equation describing the electron-hole pairs of QDs. The numerical solutions are described using a basis set composed of the eigenstates of the Schrödinger equation; they are thus equivalent to analytical solutions. This semi-analytical numerical method made it simple and reliable to evaluate the dependency of QD characteristics on the QD core size and electric field intensity. As the QD core diameter changed from 9.9 to 2.5 nm, the light emission wavelength of CdSe core-only QDs varied from 262.9 to 643.8 nm, and that of CdSe/ZnS core/shell QDs from 279.9 to 697.2 nm. On application of an electric field of 8 × 10⁵ V/cm, the emission wavelengths of green-emitting CdSe and CdSe/ZnS QDs increased by 7.7 and 3.8 nm, respectively. This semi-analytical numerical analysis will aid the choice of QD size and material, and promote the development of improved QD light-emitting devices.

• Journal of Information Display
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• v.13 no.2
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• pp.91-95
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• 2012

Indium phosphide (InP) quantum dots (QDs) are considered alternatives to Cd-containing QDs for application in light-emitting devices. The multishell coating with ZnSe/ZnS was shown to improve the photoluminescence quantum yield (QY) of InP QDs more strongly than the conventional ZnS shell coating. Structural proof for this system was provided by X-ray diffraction and transmission electron microscopy. QY values in the range of 50-70% along with peak widths of 45-50 nm can be routinely achieved, making the optical performance of InP/ZnSe/ZnS QDs comparable to that of Cd-based QDs. The fabrication of a working electroluminescent light-emitting device employing the reported material demonstrated the feasibility of the desired application.

• Bulletin of the Korean Chemical Society
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• v.31 no.6
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• pp.1555-1560
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• 2010

Quantum dots (QDs) are extensively employed for biomedical research as a fluorescence reporter and their use for various labeling applications will continue to increase as they are preferred over conventional labeling methods for various reasons. However, concerns have been raised over the toxicity of these particles in the biological system. Till date no thorough investigation has been carried out to identify the molecular signatures of QD mediated toxicity. In this study we evaluated the toxicity of CdSe, $Cd_{1-x}Zn_xS$/ZnS and CdSe/ZnS quantum dots having different spectral properties (red, blue, green) using human embryonic kidney fibroblast cells (HEK293). Cell viability assay for both short and long duration exposure show concentration material dependent toxicity, in the order of CdSe > $Cd_{1-x}Zn_xS$/ZnS > CdSe/ZnS. Genome wide changes in the expression of genes upon QD exposure was also analyzed by wholegenome microarray. All the three QDs show increase in the expression of genes related to apoptosis, inflammation and response towards stress and wounding. Further comparison of coated versus uncoated CdSe QD-mediated cell death and molecular changes suggests that ZnS coating could reduce QD mediated cytotoxicity to some extent only.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.6
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• pp.454-460
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• 2021

In this work, we synthesized alloy-core InZnP quantum dots, which are more efficient than single-core InP quantum dots, using a solution process method. The effect of synthesis conditions of alloy core on optical properties was investigated. We also investigated the conditions that make up the gradient shell to minimize defects caused by lattice mismatch between the InZnP core and ZnS is 7.7%. The stable synthesis temperature of the InZnP alloy core was 200℃. Quantum dots consisting of three layered ZnSe gradient shell and single layered ZnS exhibited the best optical property. The properties of quantum dots synthesized in 100 ml and in 2,000 ml flasks were almost equal.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.215-215
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• 2014

Red color light emitting diodes (LEDs) were fabricated using CdSe/CdZnS quantum dots (QDs). During the device fabrication process, oxygen plasma treatment on the ITO surface was performed to improve the interfacial contact between ITO anode and the hole injection layer. CdSe/CdZnS quantum dots were cross-linked to remove their surrounded organic surfactants. The device shows red emission at 622 nm, which is consistent with the dimension of the QDs (band gap=1.99 eV). The luminance shows 6026% improvement compared with that of LEDs fabricated without oxygen plasma treatment and quantum dots cross-linking process. This approach would be useful for the fabrication of high-performance QLEDs with ITO electrode and PEDOT:PSS hole injection layers.

• Journal of Powder Materials
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• v.25 no.2
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• pp.132-136
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• 2018

Core/shell CdSe/ZnS quantum dots (QDs) are synthesized by a microfluidic reactor-assisted continuous reactor system. Photoluminescence and absorbance of synthesized CdSe/ZnS core/shell QDs are investigated by fluorescence spectrophotometry and online UV-Vis spectrometry. Three reaction conditions, namely; the shell coating reaction temperature, the shell coating reaction time, and the ZnS/CdSe precursor volume ratio, are combined in the synthesis process. The quantum yield of the synthesized CdSe QDs is determined for each condition. CdSe/ZnS QDs with a higher quantum yield are obtained compared to the discontinuous microfluidic reactor synthesis system. The maximum quantum efficiency is 98.3% when the reaction temperature, reaction time, and ZnS/CdSe ratio are $270^{\circ}C$, 10 s, and 0.05, respectively. Obtained results indicate that a continuous synthesis of the Core/shell CdSe/ZnS QDs with a high quantum efficiency could be achieved by isolating the reaction from the external environment.

• Journal of the Optical Society of Korea
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• v.10 no.4
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• pp.184-187
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• 2006

For resonant excitation of the ground state $1s^e-1S^h_{3/2}$, dynamics of 'the electron-hole pair in a CdSe quantum dot was investigated by degenerate pump-probe measurement. At low e-h pair densities, the decay of $1s^e-1S^h_{3/2}$ state is dominated by radiative recombination. As the number of the electron-hole pairs increases, new decay features become significant. Theoretical comparison suggests this is attributed to the bi-molecular and Auger-type scattering.

• Bulletin of the Korean Chemical Society
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• v.34 no.3
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• pp.856-862
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• 2013

The photoanode electrode of $TiO_2$ nanotubes (NTs) anchored with ZnS/CdSSe/CdS quantum dots (QDs) was prepared by anodization of Ti metal and successive ionic layer adsorption and reaction (SILAR) procedure. The tuning of the band gap of CdSSe was done with controlled composition of Cd, S, or Se during the SILAR. A ladder-like energy structure suitable for carrier transfer was attained with the photoanode electrode. The power conversion efficiency (PCE) of our solar cell fabricated with the regular array of $TiO_2$ NTs anchored with CdSSe/CdS or CdSe/CdS QDs [i.e., (CdSSe/CdS/$TiO_2NTs$) or (CdSe/CdS/$TiO_2NTs$)] was PCE = 3.49% and 2.81% under the illumination at 100 mW/$cm^2$, respectively. To protect the photocorrosion of our solar cell from the electrolyte and to suppress carrier recombination, ZnS was introduced onto CdSSe/CdS. The PCE of our solar cell with the structure of a photoanode electrode, (ZnS/CdSSe/CdS/$TiO_2$ NTs/Ti) was 4.67% under illumination at 100 mW/$cm^2$.