Visible-to-UV triplet-triplet annihilation upconversion from a thermally activated delayed fluorescence/pyrene pair in an air-saturated solution

이학래,이명수,박현,한원식,김재혁 한국화학공학회 2019 Korean Journal of Chemical Engineering Vol.36 No.11

Despite increasing use of triplet-triplet annihilation upconversion (TTA-UC) of low-energy visible light, the generation of ultraviolet (UV) photons by TTA remains challenging because of the difficulty in finding sensitizers and acceptors with suitable energy levels. Here, we report efficient, photostable visible-to-UV TTA-UC in an air-saturated solution using a new pair with suitable energy levels: a thermally activated delayed fluorescence (TADF) molecule and pyrene. 4CzIPN, which has extremely small energy difference ΔEST (0.083 eV), was used as the TADF sensitizer to promote effective triplet energy transfer to the acceptor. When oleic acid was used as an effective singlet oxygen receptor in an air-saturated solution, the 4CzIPN/pyrene pair exhibited bright upconverted emission at 370-430 nm under 445 nm laser excitation, but no noticeable upconverted emission was observed when 4CzIPN was paired with previously reported UV-emitting acceptors [2,5-diphenyloxazole (PPO), p-terphenyl, and p-quaterphenyl]. TTA was confirmed by the quadratic dependence of the upconverted emission intensity on the 445 nm laser power density. The maximum quantum yield of the upconverted emission from the 4CzIPN/pyrene pair was 0.66%, which is considerable when compared with that of a previously reported visible-to-UV TTA-UC system with a biacetyl/PPO pair (0.58%).

Characterization of the ZnSe/ZnS Core Shell Quantum Dots Synthesized at Various Temperature Conditions and the Water Soluble ZnSe/ZnS Quantum Dot

황청수,조일희 대한화학회 2005 Bulletin of the Korean Chemical Society Vol.26 No.11

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 ûC, and for the optimum shell capping, the temperature was 135 ûC. 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.

Enhanced UV-Light Emission in ZnO/ZnS Quantum Dot Nanocrystals

김기은,김웅,성윤모,Kim, Ki-Eun,Kim, Woong,Sung, Yun-Mo Materials Research Society of Korea 2008 한국재료학회지 Vol.18 No.12

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.

Characterization of the ZnSe/ZnS Core Shell Quantum Dots Synthesized at Various Temperature Conditions and the Water Soluble ZnSe/ZnS Quantum Dot

Hwang, Cheong-Soo,Cho, Ill-Hee Korean Chemical Society 2005 Bulletin of the Korean Chemical Society Vol.26 No.11

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.

Enhanced near-UV emission from self-catalytic brush-like GaN nanowires

Kim, S.,Park, S.,Ko, H.,Jeong, B.Y.,Lee, C. North-Holland 2014 Materials letters Vol.116 No.-

Recently, the enhanced field emission, photocatalytic activity and blue shift in UV emission of branched GaN nanowire structures were reported. Nevertheless, enhanced luminescence in branched GaN nanowires have not been reported despite the importance of short-wavelength emission. This paper reports synthesis of self-catalytic brush-like GaN nanowires exhibiting enhanced near-ultraviolet (NUV) emission. The diameters of the branches in the brush-like nanowires ranged from 3 to 14nm, whereas those of backbones ranged from 30 to 80nm. In contrast, the diameters of pristine nanowires were in a similar range to those of the backbones in the brush-like nanowires. The brush-like GaN nanowires showed significantly enhanced NUV emission compared to pristine GaN nanowires. This enhanced NUV emission might be due to the quantum confinement of excitons caused by the branches in the brush-like nanowires with diameters smaller than the Bohr exciton radius.

Synthesis and characterization of various cyanostilbene-based fluorophores

정재욱,이건형 한국공업화학회 2018 한국공업화학회 연구논문 초록집 Vol.2018 No.0

Aggregation-induced emission (AIE) has been widely used for the detection of various analytes in biological samples. Among AIE fluorophores, cyanostilbene-based fluorophores have received much attention for their unique properties such as visible light excitation, significant red-emission in the aggregations, and high stability. To investigate the emission property depending on the substituents on the cyanostilbene, cyanostilbene-based fluorophores with various substituents were synthesized and their fluorescent properties were characterized in aggregation and non-aggregation states. Interestingly, amine substituent on the cyanostilbene showed a small emission in purely aqueous solution, whereas nitro substituents on the cyanostilene exhibited a significant red-emission in purely aqueous solution. Fluorescent titration, UV-vis titration, and DLS measurements showed the role of the substituent effects on the aggregation-induced emission of cyanostilbene-based fluorophores.

Proton-Induced Scintillation Properties of a UV-Cured Plastic Scintillator

Sunghwan Kim,Youl-Hun Seoung 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.8

In this study, we fabricated and characterized a UV-curable plastic scintillation resin for 3D printing technology. The resin for 3D printing was prepared by using the co-polymers MMA (methyl meta-acrylate, DHPA (dipentaerythritol hexa-acrylate), naphthalene and PPO (2,5- diphenyloxazole) organic scintillator obtained from Sigma Aldrich. Irgacure 184 (BASF Co.) was used as a photo-initiator. Protons and X-ray-induced luminescence spectra of the UV-cured plastic scintillator were measured. For the emission spectrum, QE65000 and USB4000 optic spectrometers (Ocean Optics) were used. The cured plastic scintillator showed an emission spectrum at wave- length between 380 and 650 nm, peaking at 405 nm and 550 nm, excited by using 100 MeV proton. The observed emission matched well with the quantum eciency curve of the photodiode. The result showed that the scintillator provided the possibility of adding 3D printing technology, and applications can be found in human dosimetry, etc.

Enhanced Field Emission from UV-Illuminated CuO Nanowires Fabricated by Thermal Oxidation of Cu Film

Jiang Zhao,Debo Wang,Yue Chen,Qiu Jin,Guoqing Wang 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2016 NANO Vol.11 No.5

Cupric Oxide (CuO) nanowires have been successfully synthesized by direct thermal oxidation of Cu film in air. The morphologies and structures of the synthesized materials are investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results imply that CuO nanowires with well vertical arrays present very narrow sharp peaks, indicating the nanowires are highly crystalline. The effect of ultraviolet (UV) illumination on the field emission characteristics of the CuO nanowires is investigated. The turn-on electric field of UV-illuminated CuO nanowires decreases and the field enhancement factor enhances.

A Novel Carbon Nanotube FED Structure and UV-Ozone Treatment

Chun, Hyun-Tae,Lee, Dong-Gu The Korean Infomation Display Society 2006 Journal of information display Vol.7 No.1

A 10" carbon nanotube field emission display device was fabricated with a novel structure with a hopping electron spacer (HES) by screen printing technique. HES plays a role of preventing the broadening of electron beams emitted from carbon nanotubes without electrical discharge during operation. The structure of the novel tetrode is composed of carbon nanotube emitters on a cathode electrode, a gate electrode, an extracting electrode coated on the top side of a HES, and an anode. HES contains funnel-shaped holes of which the inner surfaces are coated with MgO. Electrons extracted through the gate are collected inside the funnel-shaped holes. They hop along the hole surface to the top extracting electrode. In this study the effects of the addition of HES on emission characteristics of field emission display were investigated. An active ozone treatment for the complete removal of residues of organic binders in the emitter devices was applied to the field emission display panel as a post-treatment.

Synthesis of AlON materials for UV emitting devices

Cho, Yujin,Koo, Jieun,Cho, Youngji,Lee, Woong,Lee, Jeungwoo,Lee, Byeongwoo,Lee, Sangtae,Chang, Jiho WILEY‐VCH Verlag 2013 Physica status solidi. PSS. C, Current topics in s Vol.10 No.5

<P><B>Abstract</B></P><P>Aluminum oxynitride (AlON), which is conventionally used as one of the ceramics with good thermal and chemical stability, has an attractive candidate for a tunable extreme UV luminous material due to its unique combination of properties and UV luminescence. In this paper, we have synthesized the novel AlON UV emitting materials, which have a wavelength from 4.29 to 4.54 eV, and discovered the core (AlON)‐shell (Al<SUB>2</SUB>O<SUB>3</SUB>) like structures in a transmission electron microscopy. Furthermore, their potential application in a UV light emitter has been demonstrated by applying the combination with a CNT field emission cold cathode, which has been made by a simple printing method. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)</P>