• Journal of the Korean Chemical Society
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• v.53 no.6
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• pp.677-682
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• 2009

ZnS:Mn/ZnS core-shell quantum dots (QDs), were synthesized via a thermal decomposition reaction of organometallic precursors in a hot solvent mixture. The synthetic conditions of the quantum dots were monitored at various reaction temperatures for the core formation, while the shell formation temperature was fixed at 135$^{\circ}C$. The obtained colloidal nanocrystals at corresponding temperatures were characterized by UV-Vis, solution photoluminescence (PL) spectroscopies, and further obtained powders were characterized by XRD, HR-TEM, and EDXS analyses. The synthetic temperature condition to obtain the best PL emission intensity for the core-shell QD was 135$^{\circ}C$, for both core and shell formation. At this temperature, solution PL spectrum showed a narrow emission peak at 583 nm with a relative PL quantum efficiency of 42.15%. In addition, the measured spherical particle sizes for the ZnS:Mn/ZnS nanocrystals via HR-TEM were in the range of 4.0 to 5.4 nm, while ellipsoidal particles were obtained at 150$^{\circ}C$.

• Journal of Powder Materials
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• v.24 no.1
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• pp.11-16
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• 2017

In this study, simple chemical synthesis of green emitting Cd-free InP/ZnS QDs is accomplished by reacting In, P, Zn, and S precursors by one-pot process. The particle size and the optical properties were tailored, by controlling various experimental conditions, including [In]/[MA] (MA: myristic acid) mole ratio, reaction temperature and reaction time. The results of ultraviolet-visible spectroscopy (UV-vis), and of photoluminescence (PL), reveal that the exciton emission of InP was improved by surface coating, with a layer of ZnS. We report the correlation between each experimental condition and the luminescent properties of InP/ZnS core/shell QDs. Transmission electron microscopy (TEM), and X-ray powder diffraction (XRD) techniques were used to characterize the as-synthesized QDs. In contrast to core nanoparticles, InP/ZnS core/shell treated with surface coating shows a clear ultraviolet peak. Besides this work, we need to study what clearly determines the shell kinetic growth mechanism of InP/ZnS core shell QDs.

• Bulletin of the Korean Chemical Society
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• v.26 no.11
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• pp.1776-1782
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• 2005

ZnSe/ZnS, UV-blue luminescent core shell quantum dots, were synthesized via a thermal decomposition reaction of organometallic zinc and solvent coordinated Selenium (TOPSe) in a hot solvent mixture. The synthetic conditions of the core (ZnSe) and the shell (ZnS) were independently studied at various reaction temperature conditions. The obtained colloidal nanocrystals at corresponding temperatures were characterized for their optical properties by UV-vis, room temperature solution photoluminescence (PL) spectroscopy, and further obtained powders were characterized by XRD, TEM, and EDXS analyses. The synthetic temperature condition to obtain the best PL emission intensity for the ZnSe core was 300 ${^{\circ}C}$, and for the optimum shell capping, the temperature was 135 ${^{\circ}C}$. At this temperature, solution PL spectrum showed a narrow emission peak at 427 nm with a PL efficiency of 15%. In addition, the measured particle sizes for the ZnSe/ZnS nanocomposite via TEM were in the range of 5 to 12 nm. Furthermore, we have synthesized water-soluble ZnSe/ZnS nanoparticles by capping the ZnSe/ZnS hydrophobic surface with mercaptoacetate (MAA) molecules. For the obtained aqueous colloidal solution, the UV-vis spectrum showed an absorption peak at 250 nm, and the solution PL emission spectrum showed a peak at 425 nm, which is similar to that for hydrophobic quantum dot ZnSe/ZnS. However, the calculated PL efficiency was relatively low (0.1%) due to the luminescence quenching by water and MAA molecules. The capping ligand was also characterized by FT-IR spectroscopy, with the carbonyl stretching peak in the mercaptoacetate molecule appearing at 1575 $cm ^{-1}$. Finally, the particle sizes of the MAA capped ZnSe/ZnS were measured by TEM, showing a range of 12 to 17 nm.

• Bulletin of the Korean Chemical Society
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• v.33 no.7
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• pp.2333-2337
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• 2012

We report the synthesis and thermal annealing of Si-core/ZnO-shell nanorods using a two-step process comprising the metal-assisted electroless etching of Si and the sputter deposition of ZnO. Transmission electron microscopy and X-ray diffraction analysis showed that the cores of the annealed core-shell nanorods were single crystal diamond cubic-type Si, whereas the shells of the annealed core-shell nanorods were single crystal wurtzite-type ZnO. The PL spectra of Si nanorods consisted of a broad red emission band and a weaker blue emission band. The major emission band of Si nanorods was shifted from 700 nm (in the red region) to 440 nm (in the violet region) by ZnO coating. The violet emission of the core-shell nanorods was enhanced in intensity considerably by annealing in an oxidizing atmosphere. The origin of the PL enhancement by annealing is also discussed.

• Journal of environmental and Sanitary engineering
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• v.14 no.2
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• pp.46-55
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• 1999

This study compared the adsorption characteristics of heavy metal ions by crab shell, treated crab shell with 2N-HCl, treated crab shell with 4%-NaOH, chitin and chitosan.Using crushed crab shell, the heavy metal ions removal rates of $Cd^{2+}$ and $Zn^{2+}$ were about 70-80% in 45minutes, but the removal rates of $Cu^{2+}$, $Cr^{6+}$ and $Pb^{2+}$ was less than 10%, 10% and 30%, respectively. For the by-products crab shell by 2N-HCl treatment, it was shown that the removal rates of $Cu^{2+}$ and $Pb^{2+}$ were about 70-80% in 45minutes reaction. But, some problems were observed, that the contained protein in crab shell was changed into gel in the mixing solution after a few hours. For the by-products of crab shell by 4%-NaOH treatment, the removal rates of Pb and Zn were about 90% in 45 minutes, and those of capacity of chitin and chitosan powder was better than those of the other by-products. The more adding to the adsorbent dosages increased the removal rates, and the adsorption reaction was rapidly occurred in a few minute. Using 1.0 wt% chitin powder, the heavy metal removal rates were ordered $Cu^{2+}$(94%) > $Zn^{2+}$(89%) > $Cd^{2+}$(88%) > $Pb^{2+}$(77%) > $Cr^{6+}$(58%) in 45 minutes. Using 1.0 wt% chitosan powder, the heavy metal removal rates were ordered $Cu^{2+}$(99%) > $Pb^{2+}$(96%) > $Cd^{2+}$(79%) > $Zn^{2+}$(71%) > $Cr${6+}$(46%) in 45minutes. The degree of degree of deacetylation by prepared chitosan was 91%.The Freundlich adsorption isotherm of $Cu^{2+}$, $Cd^{2+}$ and $Zn^{2+}$, when it was applied to 1.0 wt% chitosan powder in minutes, can be acceptable very strictly. The equation constant (1/n) for $Cu^{2+}$, $Cd^{2+}$ and $Zn^{2+}$ were 0.54 0.41 and 0.23 respectively.

• Korean Journal of Materials Research
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• v.18 no.12
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• pp.640-644
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• 2008

ZnO/ZnS core/shell nanocrystals (${\sim}5-7\;nm$ in diameter) with a size close to the quantum confinement regime were successfully synthesized using polyol and thermolysis. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) analyses reveal that they exist in a highly crystalline wurtzite structure. The ZnO/ZnS nanocrystals show significantly enhanced UV-light emission (${\sim}384\;nm$) due to effective surface passivation of the ZnO core, whereas the emission of green light (${\sim}550\;nm$) was almost negligible. They also showed slight photoluminescence (PL) red-shift, which is possibly due to further growth of the ZnO core and/or the extension of the electron wave function to the shell. The ZnO/ZnS core/shell nanocrystals demonstrate strong potential for use as low-cost UV-light emitting devices.

• Journal of the Korean Ceramic Society
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• v.55 no.5
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• pp.510-514
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• 2018

Colloidal semiconductor quantum dots (QDs), because of the novel optical and electrical properties that stem from their three-dimensional confinement, have attracted great interest for their potential applications in such fields as bio-imaging, display, and opto-electronics. However, many semiconductors that can be exploited for QD applications contain toxic elements. Herein, we synthesized non-toxic ZnTe/ZnSe (core/shell) type-II QDs by pyrolysis method. Because of the unique type-II character of these QDs, their emission can range over an extended wavelength regime, showing photoluminescence (PL) from 450 nm to 580 nm. By optimizing the ZnSe shell growth condition, resulting ZnTe/ZnSe type-II QDs shows PL quantum yield up to ~ 25% with 35 nm PL bandwidth. Using a simple two step cation exchange reaction, we also fabricated ZnTe/ZnSe type-II QDs with absorption extended over the whole visible region. The visible-light sensitized heavy metal free ZnTe/ZnSe type-II QDs can be relevant for opto-electronic applications such as displays, light emitting diodes, and bio-imaging probes.

• Journal of the Korean Chemical Society
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• v.59 no.5
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• pp.397-406
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• 2015

ZnO, II-VI group inorganic compound semi-conductor, has been receiving much attention due to its wide applications in various fields. Since the ZnO has 3.37 eV of a wide band gap and 60 meV of big excitation binding energy, it is well-known material for various uses such the optical property, a semi-conductor, magnetism, antibiosis, photocatalyst, etc. When applied in the field of photocatalyst, many research studies have been actively conducted regarding magnetic materials and the core-shell structure to take on the need of recycling used materials. In this paper, magnetic core-shell ZnFe₂O₄@SiO₂ nanoparticles (NPs) have been successfully synthesized through three steps. In order to analyze the structural characteristics of the synthesized substances, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR) were used. The spinel structure of ZnFe₂O₄ and the wurtzite structure of ZnO were confirmed by XRD, and ZnO production rate was confirmed through the analysis of different concentrations of the precursors. The surface change of the synthesized materials was confirmed by SEM. The formation of SiO₂ layer and the synthesis of ZnFe₂O₄@ZnO@SiO₂ NPs were finally verified through the bond of Fe-O, Zn-O and Si-O-Si by FT-IR. The magnetic property of the synthesized materials was analyzed through the vibrating sample magnetometer (VSM). The increase and decrease in the magnetism were respectively confirmed by the results of the formed ZnO and SiO₂ layer. The photocatalysis effect of the synthesized ZnFe₂O₄ @ZnO@SiO₂ NPs was experimented in a black box (dark room) using methylene blue (MB) under UV irradiation.

• Proceeding of EDISON Challenge
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• 2017.03a
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• pp.480-483
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• 2017

양자막대를 이용한 디스플레이 활용에서, Blue를 발광하는 CdZnS의 합성에서 ZnS의 road에 shell을 형성하기 위해서는 Oleamine (OAm) 리간들를 사용한다. 반면, Oleic Acid (OA) 리간드를 사용하면 shell의 합성이 잘 안되는데, 본 논문은 이러한 이유를 제 1원리 계산을 바탕으로 설명해 놓았다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.241-241
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• 2014

$SnO_2-core/Zn-shell$ heteronanowires were fabricated by a two-step process: thermal evaporation of Sn powders and employing a sputtering technique with a Zn target. X-ray diffraction, high-resolution transmission electron microscopy, and EDX spectra coincidentally indicated that the shell layer comprised the Zn phase. From Gaussian deconvolution studies, we observed that photoluminescence (PL) spectra consisted of yellow, green, and ultraviolet (UV) emission bands, regardless of shell-coating. We speculated the possible mechanisms of these emission peaks.