Unconventional Three-Armed Luminogens Exhibiting Both Aggregation-Induced Emission and Thermally Activated Delayed Fluorescence Resulting in High-Performing Solution-Processed Organic Light-Emitting Diodes

Park, Seo Yeon,Choi, Suna,Park, Gi Eun,Kim, Hyung Jong,Lee, Chiho,Moon, Ji Su,Kim, Si Woo,Park, Sungnam,Kwon, Jang Hyuk,Cho, Min Ju,Choi, Dong Hoon American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.17

<P>In this work, three-armed luminogens <B>IAcTr-out</B> and <B>IAcTr-in</B> were synthesized and used as emitters bearing triazine and indenoacridine moieties in thermally activated delayed fluorescence organic light-emitting diodes (OLEDs). These molecules could form a uniform thin film via the solution process and also allowed the subsequent deposition of an electron transporting layer either by vacuum deposition or by an all-solution coating method. Intriguingly, the new luminogens displayed aggregation-induced emission (AIE), which is a unique photophysical phenomenon. As a nondoped emitting layer (EML), <B>IAcTr-in</B> showed external quantum efficiencies (EQEs) of 11.8% for the hybrid-solution processed OLED and 10.9% for the all-solution processed OLED with a low efficiency roll-off. This was evident by the higher photoluminescence quantum yield and higher rate constant of reverse intersystem crossing of <B>IAcTr-in</B>, as compared to <B>IAcTr-out</B>. These AIE luminogens were used as dopants and mixed with the well-known host material 1,3-bis(<I>N</I>-carbazolyl)benzene (mCP) to produce a high-efficiency OLED with a two-component EML. The maximum EQE of 17.5% was obtained when using EML with <B>IAcTr-out</B> doping (25 wt %) into mCP, and the OLED with EML bearing <B>IAcTr-in</B> and mCP showed a higher maximum EQE of 18.4% as in the case of the nondoped EML-based device.</P> [FIG OMISSION]</BR>

Mass of heavy-light mesons in a constituent quark picture with partially restored chiral symmetry

Park, Aaron,Gubler, Philipp,Harada, Masayasu,Lee, Su Houng,Nonaka, Chiho,Park, Woosung American Physical Society 2016 Physical review. D Vol.93 No.5

<P>We probe effects of the partial chiral symmetry restoration to the mass of heavy-light mesons in a constituent quark model by changing the constituent quark mass of the light quark. Due to the competing effect between the quark mass and the linearly rising potential, whose contribution to the energy increases as the quark mass decreases, the heavy-light meson mass has a minimum value near the constituent quark mass typically used in the vacuum. Hence, the meson mass increases as one decreases the constituent quark mass consistent with recent QCD sum rule analyses, which show an increasing D meson mass as the chiral order parameter decreases.</P>

Thin film fabrication of upconversion lanthanide-doped NaYF₄ by a sol-gel method and soft lithographical nanopatterning

Park, Heeyeon,Yoo, Gang Yeol,Kim, Min-Seop,Kim, Kein,Lee, Chiho,Park, Sungnam,Kim, Woong Elsevier 2017 Journal of Alloys and Compounds Vol.728 No.-

<P><B>Abstract</B></P> <P>Lanthanide-doped NaYF<SUB>4</SUB> is one of the most efficient upconversion materials and fabrication of high-quality thin-films of this material would be useful in various applications. However, it has been a great challenge to fabricate thin films and/or nanopatterns of this material. In this work, we demonstrate the successful fabrication of the NaYF<SUB>4</SUB> thin films and nanopatterns via a sol-gel process and soft lithography. Upconversion of 980 nm near-infrared wavelength to various visible wavelengths (yellow, green, blue, etc.) has been realized using dopants and/or multilayered film structures. Nanopatterns enhance the light out-coupling efficiency and thus the upconversion intensity by a factor of ∼ 2–3. The fabrication of high-quality films and patterns is enabled by understanding the dependence of the structural, optical, chemical, and thermal properties of the precursor materials on the temperature. Our results will be an important basis for both scientific and technological advances in wavelength conversion in various areas such as displays, optoelectronics, photonics, and photovoltaics.</P> <P><B>Highlights</B></P> <P> <UL> <LI> High quality NaYF<SUB>4</SUB> thin films are successfully fabricated via a sol-gel process. </LI> <LI> Phase transition from cubic to hexagonal occurs at 340 °C. </LI> <LI> The process is compatible with soft lithography by which nanopatterns are generated. </LI> <LI> The nanopatterns enhance the light out-coupling efficiency. </LI> <LI> Lanthanide dopants enable upconversion of infrared to various visible wavelengths. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

The study of physical mixing effect to improve the activity of NiCo-based OER elctrocatalyst

Eon-ju Park,Sungjun Heo,Chiho Kim,Song Jin,Jae-Yeop Jeong,Shin-woo Myeong,Ho-seok Lee,Jae-hun Lee,Nam-in Kim,Jun Young park,Jooyoung Lee,Oi Lun Helena Li,Sung Mook Choi 한국표면공학회 2023 한국표면공학회 학술발표회 초록집 Vol.2023 No.11-1

Intense pulsed white light assisted fabrication of Co-CoOx core-shell nanoflakes on graphite felt for flexible hybrid supercapacitors

Park, Changyong,Hwang, Jeonguk,Hwang, Yeon-Taek,Song, Chiho,Ahn, Suhyun,Kim, Hak-Sung,Ahn, Heejoon Elsevier 2017 ELECTROCHIMICA ACTA Vol.246 No.-

<P><B>Abstract</B></P> <P>In this work, cobalt/cobalt oxide (Co-CoOx) core-shell nanoflakes were directly grown on flexible graphite felt (GF) using a facile one-step intense pulsed white light (IPWL) irradiation method. They were then used as a battery-type positive electrode for a high-performance asymmetric hybrid supercapacitor, which exhibited high rate capability and a long cycle life. The interconnected Co-CoOx thin nanoflakes grown on the GF offer large reaction sites and enough space for easy OH<SUP>−</SUP> ion transport due to their 3-dimensionally interconnected network structures. Cobalt metal at the core of the nanoflakes, directly connected to the current collector of the GF, provided pathways for electrons between the cobalt oxide and GF, leading to low internal resistance and high rate capability. The Co-CoOx/GF electrode had a high specific capacity of 108mAhg<SUP>−1</SUP> at a specific current of 1Ag<SUP>−1</SUP> and maintained a capacity of 71mAhg<SUP>−1</SUP> at a high specific current of 20Ag<SUP>−1</SUP>. A two-terminal asymmetric hybrid supercapacitor, assembled using Co-CoOx/GF as the positive electrode and activated carbon as the negative electrode with gel-electrolyte (PVA/KOH), exhibited an energy density of 30.1 Wh kg<SUP>−1</SUP> at a power density of 0.86kWkg<SUP>−1</SUP> and a high retention of 13.0 Wh kg<SUP>−1</SUP> at a power density of 20.4kWkg<SUP>−1</SUP>. In addition, the asymmetric device showed excellent cycling stability, with 114% capacity retention after 10,000 cycles.</P>

Off-Road Machinery System Engineering ; Impact of Sound Insulation in a Combine Cabin

( Chiho Kim ),( Hojun Jung ),( Jinseok Jo ),( Myongil Kim ),( Bongho Lee ),( Taejong Park ),( Kwangwook Seo ),( Hyeontae Kim ) 한국농업기계학회 2015 바이오시스템공학 Vol.40 No.3

Purpose: Recently, environmental pollution and safety problems in agricultural production have become important issues. Initially, bio-production machines focused on high production efficiency rather than workers’ safety and comfort, but this trend slowly has changed as time went on. Methods: This study was carried out to identify sound efficiently and reliably for noise reduction by using a combine cabin model. Ethylene propylene diene monomer (M-class) rubber (EPDM) was applied to improve noise reduction performance from parts connected directly to the front, rear, left side, and bottom side of the cabin. Results: As a result, an average noise reduction of 1.85 dB was achieved in the normal hearing range between 500 Hz to 2 kHz. Conclusions: Reducing the cabin noise levels can reduce a worker``s fatigue, improve working environment, and contribute to future low-noise and high-quality cabin environment.

BOM구조를 고려한 Job Shop 일정계획에 관한 연구

문치호(Chiho Moon),서진우(Seo Jinwu),박진우(Jinwoo Park) 한국경영과학회 2009 한국경영과학회 학술대회논문집 Vol.2009 No.10

제품을 적시에 받기를 원하는 고객의 요구와 기업들 간의 경쟁이 심화되면서 납기의 중요성이 강조되고 있다. 이에 따라 확실한 납기를 보장할 수 있는 능력이 기업의 경쟁력으로 부상하고 있다. 일반적인 Job shop 일정계획 문제에서는 BOM(Bill of Material)구조를 고려하지 않는 경우가 많다. 하지만 실제 생산 공정에서 BOM 구조를 갖지 않는 제품은 많지 않다. 따라서 BOM 구조를 고려하지 않는 일정계획 문제는 현실에 적용하기 어렵다. 본 연구에서는 다단계 작업구조를 대상으로 납기 지연을 최소화하는 우선순위 규칙을 제시한다.

Acid–base equilibrium dynamics in methanol and dimethyl sulfoxide probed by two-dimensional infrared spectroscopy

Lee, Chiho,Son, Hyewon,Park, Sungnam The Royal Society of Chemistry 2015 Physical chemistry chemical physics Vol.17 No.27

<P>Two-dimensional infrared (2DIR) spectroscopy, which has been proven to be an excellent experimental method for studying thermally-driven chemical processes, was successfully used to investigate the acid dissociation equilibrium of HN<SUB>3</SUB> in methanol (CH<SUB>3</SUB>OH) and dimethyl sulfoxide (DMSO) for the first time. Our 2DIR experimental results indicate that the acid–base equilibrium occurs on picosecond timescales in CH<SUB>3</SUB>OH but that it occurs on much longer timescales in DMSO. Our results imply that the different timescales of the acid–base equilibrium originate from different proton transfer mechanisms between the acidic (HN<SUB>3</SUB>) and basic (N<SUB>3</SUB><SUP>−</SUP>) species in CH<SUB>3</SUB>OH and DMSO. In CH<SUB>3</SUB>OH, the acid–base equilibrium is assisted by the surrounding CH<SUB>3</SUB>OH molecules which can directly donate H<SUP>+</SUP> to N<SUB>3</SUB><SUP>−</SUP> and accept H<SUP>+</SUP> from HN<SUB>3</SUB> and the proton migrates through the hydrogen-bonded chain of CH<SUB>3</SUB>OH. On the other hand, the acid–base equilibrium in DMSO occurs through the mutual diffusion of HN<SUB>3</SUB> and N<SUB>3</SUB><SUP>−</SUP> or direct proton transfer. Our 2DIR experimental results corroborate different proton transfer mechanisms in the acid–base equilibrium in protic (CH<SUB>3</SUB>OH) and aprotic (DMSO) solvents.</P> <P>Graphic Abstract</P><P>Two-dimensional infrared (2DIR) spectroscopy was successfully used to investigate the acid dissociation equilibrium of HN<SUB>3</SUB> in methanol (CH<SUB>3</SUB>OH) and dimethyl sulfoxide (DMSO). <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5cp02368h'> </P>

Impact of Sound Insulation in a Combine Cabin

Kim, Chiho,Jung, Ho Jun,Jo, Jin Seok,Kim, Myong il,Lee, Bongho,Park, Tae Jong,Seo, Kwangwook,Kim, Hyeon Tae Korean Society for Agricultural Machinery 2015 바이오시스템공학 Vol.40 No.3

Purpose: Recently, environmental pollution and safety problems in agricultural production have become important issues. Initially, bio-production machines focused on high production efficiency rather than workers' safety and comfort, but this trend slowly has changed as time went on. Methods: This study was carried out to identify sound efficiently and reliably for noise reduction by using a combine cabin model. Ethylene propylene diene monomer (M-class) rubber (EPDM) was applied to improve noise reduction performance from parts connected directly to the front, rear, left side, and bottom side of the cabin. Results: As a result, an average noise reduction of 1.85 dB was achieved in the normal hearing range between 500 Hz to 2 kHz. Conclusions: Reducing the cabin noise levels can reduce a worker's fatigue, improve working environment, and contribute to future low-noise and high-quality cabin environment.

Vibrational probing of the hydrogen-bond structure and dynamics of water in aqueous NaPF₆ solutions

Lee, Chiho,Nam, Dayoung,Park, Sungnam The Royal Society of Chemistry 2015 New Journal of Chemistry Vol.39 No.5

<P>Direct measurements of the individual dynamics of water in bulk and ionic hydration shells in aqueous ionic solutions are quite experimentally challenging because the different subsets of water in bulk and ionic hydration shells are not spectrally well-resolved in most aqueous ionic solutions. In contrast, the different subsets of water in the bulk, cationic hydration shell, and anionic hydration shell in aqueous NaPF<SUB>6</SUB> solutions were found to be spectrally well distinct. Such spectral features allowed us to study the individual dynamics of the different subsets of water in aqueous NaPF<SUB>6</SUB> solutions. In this work, we studied the hydrogen-bond (H-bond) structure and dynamics of water in aqueous NaPF<SUB>6</SUB> solutions at different NaPF<SUB>6</SUB> concentrations by FTIR, Raman, and IR pump–probe spectroscopy. Three different subsets of water in the bulk, cationic hydration shell, and anionic hydration shell were found to have their own characteristic hydroxyl stretch peaks (eigen spectra) in FTIR and Raman spectra and have unique vibrational lifetimes independent of NaPF<SUB>6</SUB> concentration. However, the orientational relaxation dynamics, <I>r</I>(<I>t</I>), were not able to be separately measured for three different subsets of water. The overall orientational relaxation times were found to be linearly dependent on the solution viscosity and were reasonably well described by the Debye–Stokes–Einstein equation. Finally, the frequency-dependent transition dipole moments of the hydroxyl (–OD) stretch vibration obtained in neat water and aqueous 3.0 M NaPF<SUB>6</SUB> solution were compared and found to be dependent on the nature of H-bonds.</P> <P>Graphic Abstract</P><P>The H-bond structures and dynamics of water in bulk and ionic hydration shells in aqueous NaPF<SUB>6</SUB> solutions were measured at different NaPF<SUB>6</SUB> concentrations. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5nj00160a'> </P>