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InP 코어 합성온도에 따른 InP/ZnS의 코어/쉘 양자점의 발광특성
서한욱,정다운,김민영,현승균,온지선,김범성,Seo, Han Wook,Jeong, Da-Woon,Kim, Min Young,Hyun, Seoung Kyun,On, Ji Sun,Kim, Bum Sung 한국분말야금학회 2017 한국분말재료학회지 (KPMI) Vol.24 No.4
In this study, we investigate the optical properties of InP/ZnS core/shell quantum dots (QDs) by controlling the synthesis temperature of InP. The size of InP determined by the empirical formula tends to increase with temperature: the size of InP synthesized at $140^{\circ}C$ and $220^{\circ}C$ is 2.46 nm and 4.52 nm, respectively. However, the photoluminescence (PL) spectrum of InP is not observed because of the formation of defects on the InP surface. The growth of InP is observed during the deposition of the shell (ZnS) on the synthesized InP, which is ended up with green-red PL spectrum. We can adjust the PL spectrum and absorption spectrum of InP/ZnS by simply adjusting the core temperature. Thus, we conclude that there exists an optimum shell thickness for the QDs according to the size.
반응 용기법을 이용한 InP/ZnS 양자점 합성과정에서 InP 코어의 성장기구
서한욱,정다운,이빈,현승균,김범성,Seo, Han wook,Jeong, Da-woon,Lee, Bin,Hyun, Seoung kyun,Kim, Bum Sung 한국분말야금학회 2017 한국분말재료학회지 (KPMI) Vol.24 No.1
This study investigates the main growth mechanism of InP during InP/ZnS reaction of quantum dots (QDs). The size of the InP core, considering a synthesis time of 1-30 min, increased from the initial 2.56 nm to 3.97 nm. As a result of applying the proposed particle growth model, the migration mechanism, with time index 7, was found to be the main reaction. In addition, after the removal of unreacted In and P precursors from bath, further InP growth (of up to 4.19 nm (5%)), was observed when ZnS was added. The full width at half maximum (FWHM) of the synthesized InP/ZnS quantum dots was found to be relatively uniform, measuring about 59 nm. However, kinetic growth mechanism provides limited information for InP / ZnS core shell QDs, because the surface state of InP changes with reaction time. Further study is necessary, in order to clearly determine the kinetic growth mechanism of InP / ZnS core shell QDs.
코로나19 사태로 인해 증가하는 아동학대 위험성: 초록우산 어린이재단 대구광역시아동보호전문기관을 중심으로
서한욱 ( Sea Han Waak ) 초록우산 어린이재단(구 한국복지재단) 2020 동광 Vol.115 No.-
본 연구는 매년 증가해오던 아동학대 신고가 코로나19 확산 영향으로 올해는 오히려 감소한 것으로 나타남에 따라 그 원인을 찾아보고, 아동학대 신고가 감소한 만큼 실제로 아동학대의 위험성이 낮아졌는지 아니면 아동학대가 발견되지 못하는 요인들이 있는지 분석해보고자 하였다. 이에 코로나19의 확산은 신고의무자인 교직원에 의한 아동학대 신고건수 감소, 가정 양육 및 원격수업으로 인한 아동과 양육자의 스트레스 증가, 코로나19 확산으로 인한 보호자의 휴업 및 실직 등 요인들을 야기함으로써 오히려 아동학대의 위험성은 높아지고 있는 것으로 나타났다. 그에 반해 코로나19의 확산으로 인해 아동보호조치를 위한 아동학대조사와 재학대 발생 방지를 위한 사례관리가 제한적이거나 중단될 수밖에 없는 상황으로 아동학대 및 재학대가 반복되고 있는 현장의 실상을 알 수 있었다. 이에 코로나19 및 포스트코로나 시대는 기존의 대면조사 및 대면상담을 통한 아동학대조사와 사례관리에 더해 비대면 언택트(Untact) 등의 수단을 적극적으로 활용하여 아동학대를 조기에 발견하고, 재학대를 방지함으로써 아동을 적절히 보호할 수 있는 새로운 형태의 아동학대 대응 방법을 요구하고 있다. This study investigated the cause of child abuse reports, which have been increasing every year, as it appears to have decreased this year due to Covid-19. In addition, this study analyzed whether the risk of child abuses actually decreased or it was not found as the number of child abuse reports decreased. Covid-19 caused risk factors of child abuse such as a decrease in the number of reports of child abuse by school teachers who are obligated to report, increased stress for children and caregivers due to home rearing and remote classes, and parents' unemployment. On the other hand, due to Covid-19, child abuse investigations for child protection and case management to prevent the occurrence of re-abuse are limited or inevitably to be stopped. As a result, in the era of post -corona, as a new type of child abuse response, an untact method is required for child abuse investigations and case management in addition to the existing face-to-face investigations and face-to-face counseling. Through the untact way, it will be available to detect child abuse early and prevent re-abuse.
ZnSe:Eu 양자점의 표면결함이 광학특성에 미치는 영향
정다운,박지영,서한욱,임경묵,성태연,김범성,Jeong, Da-Woon,Park, Ji Young,Seo, Han Wook,Lim, Kyoung-Mook,Seong, Tae-Yeon,Kim, Bum Sung 한국분말야금학회 2016 한국분말재료학회지 (KPMI) Vol.23 No.5
Quantum dots (QDs) are capable of controlling the typical emission and absorption wavelengths because of the bandgap widening effect of nanometer-sized particles. These phosphor particles have been used in optical devices, photovoltaic devices, advanced display devices, and several biomedical complexes. In this study, we synthesize ZnSe QDs with controlled surface defects by a heating-up method. The optical properties of the synthesized particles are analyzed using UV-visible and photoluminescence (PL) measurements. Calculations indicate nearly monodisperse particles with a size of about 5.1 nm at $260^{\circ}C$ (full width at half maximum = 27.7 nm). Furthermore, the study results confirm that successful doping is achieved by adding $Eu^{3+}$ preparing the growth phase of the ZnSe:Eu QDs when heating-up method. Further, we investigate the correlation between the surface defects and the luminescent properties of the QDs.
마이크로리액터를 이용한 전구체 유속에 따른 CdSe/ZnS 양자점의 광학특성
박지영,정다운,주원,서한욱,좌용호,김범성,Park, Ji Young,Jeong, Da-Woon,Ju, Won,Seo, Han Wook,Cho, Yong-Ho,Kim, Bum Sung 한국분말야금학회 2016 한국분말재료학회지 (KPMI) Vol.23 No.2
High-quality colloidal CdSe/ZnS (core/shell) is synthesized using a continuous microreactor. The particle size of the synthesized quantum dots (QDs) is a function of the precursor flow rate; as the precursor flow rate increases, the size of the QDs decreases and the band gap energy increases. The photoluminescence properties are found to depend strongly on the flow rate of the CdSe precursor owing to the change in the core size. In addition, a gradual shift in the maximum luminescent wave (${\lambda}_{max}$) to shorter wavelengths (blue shift) is found owing to the decrease in the QD size in accordance with the quantum confinement effect. The ZnS shell decreases the surface defect concentration of CdSe. It also lowers the thermal energy dissipation by increasing the concentration of recombination. Thus, a relatively high emission and quantum yield occur because of an increase in the optical energy emitted at equal concentration. In addition, the maximum quantum yield is derived for process conditions of 0.35 ml/min and is related to the optimum thickness of the shell material.