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Light-emitting diode

Lixia Guo, Xiaoju Wang, Liheng Feng
A blue emitter, 3,3'-(2,2'-dimethoxy-[1,1'-binaphthalene]-6,6'-diyl)bis(9-benzyl-9H-carbazole), was synthesized by Suzuki coupling reaction. The photophysical properties of the emitter in solution were firstly investigated by UV-Vis absorption and fluorescence emission techniques. The results indicate that the emitter has excellent optical and electron transfer properties. The maximum absorption and emission peaks of the emitter are 302 nm and 406 nm with 67.4% fluorescence quantum yield in chloroform, respectively...
May 10, 2018: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
Byeongho Park, Heehong Yang, Tai Hwan Ha, Hyun Seo Park, Seung Ja Oh, Yong-Sang Ryu, Youngho Cho, Hyo-Suk Kim, Juyeong Oh, Dong Kyu Lee, Chulki Kim, Taikjin Lee, Minah Seo, Jaebin Choi, Young Min Jhon, Deok Ha Woo, Seok Lee, Seok Hwan Kim, Hyuk-Jae Lee, Seong Chan Jun, Hyun Seok Song, Tai Hyun Park, Jae Hun Kim
Photosensitive materials contain biologically engineered elements and are constructed using delicate techniques, with special attention devoted to efficiency, stability, and biocompatibility. However, to date, no photosensitive material has been developed to replace damaged visual-systems to detect light and transmit the signal to a neuron in the human body. In the current study, artificial nanovesicle-based photosensitive materials are observed to possess the characteristics of photoreceptors similar to the human eye...
May 18, 2018: Advanced Materials
Han Eol Lee, JeHyuk Choi, Seung Hyun Lee, Minju Jeong, Jung Ho Shin, Daniel J Joe, DoHyun Kim, Chang Wan Kim, Jung Hwan Park, Jae Hee Lee, Daesoo Kim, Chan-Soo Shin, Keon Jae Lee
Flexible inorganic-based micro light-emitting diodes (µLEDs) are emerging as a significant technology for flexible displays, which is an important area for bilateral visual communication in the upcoming Internet of Things era. Conventional flexible lateral µLEDs have been investigated by several researchers, but still have significant issues of power consumption, thermal stability, lifetime, and light-extraction efficiency on plastics. Here, high-performance flexible vertical GaN light-emitting diodes (LEDs) are demonstrated by silver nanowire networks and monolithic fabrication...
May 18, 2018: Advanced Materials
Lin Wang, Baiquan Liu, Xin Zhao, Hilmi Volkan Demir, Haoshuang Gu, Handong Sun
All-inorganic cesium halide perovskite nanocrystals have attracted booming interests in optoelectronic applications for the sake of the readily adjustable bandgaps, high photoluminescence quantum yield, pure color emission and affordable cost. However, due to the ineluctable utilization of organic surfactants during the synthesis, the structural and optical properties of CsPbBr3 nanocrystals degrade upon transforming from colloidal solutions to solid thin films, which plagues the device operation. Here, we develop a novel solvent-assisted surface engineering strategy, producing high quality CsPbBr3 thin films for device applications...
May 18, 2018: ACS Applied Materials & Interfaces
Dongdong Zhang, Xiaozeng Song, Haoyuan Li, Minghan Cai, Zhengyang Bin, Tianyu Huang, Lian Duan
Fluorescent organic light-emitting diodes with thermally activated delayed fluorescent sensitizers (TSF-OLEDs) have aroused wide attention, the power efficiencies of which, however, are limited by the mutual exclusion of high electron-transport mobility and large triplet energy of electron-transporting materials (ETMs). Here, an asymmetric anthracene derivative with electronic properties manipulated by different side groups is developed as an ETM to promote TSF-OLED performances. Multiple intermolecular interactions are observed, leading to a kind of "cable-like packing" in the crystal and favoring the simultaneous realization of high electron-transporting mobility and good exciton-confinement ability, albeit the low triplet energy of the ETM...
May 17, 2018: Advanced Materials
Brent W Moloughney, Gayle E Bursey, Rebecca B Fortin, Maria G Morais, Khanh Thi Dang
PURPOSE: Evaluate the incremental impact of environmental stairwell enhancements on stair usage in addition to prompts. DESIGN: Phased, nonrandomized, quasi-experimental intervention. SETTING: Two 6-story and one 8-story municipal government office buildings-each with 2 stairwells. PARTICIPANTS: Approximately 2800 municipal employees and 1000 daily visitors. INTERVENTION: All stairwells received door wraps and point-of-decision and wayfinding prompts...
January 1, 2018: American Journal of Health Promotion: AJHP
Franziska Steudel, Jacqueline A Johnson, Charles E Johnson, Stefan Schweizer
The application of Mössbauer spectroscopy to luminescent materials is described. Many solids doped with europium are luminescent, i.e., when irradiated with light they emit light of a longer wavelength. These materials therefore have practical applications in tuning the light output of devices like light emitting diodes. The optical properties are very different for the two possible valence states Eu 2 + and Eu 3 + , the former producing ultraviolet/visible light that shifts from violet to red depending on the host and the latter red light, so it is important to have a knowledge of their behavior in a sample environment...
May 17, 2018: Materials
Xi Yang, Bo Sun, Zili Wang, Cheng Qian, Yi Ren, Dezhen Yang, Qiang Feng
The lifetime prediction using accelerated degradation test (ADT) method has become a main issue for white light emitting diodes applications. This paper proposes a novel lifetime model for light emitting diodes (LEDs) under thermal and electrical stresses, where the junction temperature and driving current are deemed the input parameters for lifetime prediction. The features of LEDs' lifetime and the law of lumen depreciation under dual stresses are combined to build the lifetime model. The adoption of thermal and electrical stresses overcomes the limitation of single stress, and junction temperature in accelerated degradation test as thermal stress is more reliable than ambient temperature in conventional ADT...
May 16, 2018: Materials
Maja Grubisic, Roy H A van Grunsven, Alessandro Manfrin, Michael T Monaghan, Franz Hölker
The increasing use of artificial light at night (ALAN) has led to exposure of freshwater ecosystems to light pollution worldwide. Simultaneously, the spectral composition of nocturnal illumination is changing, following the current shift in outdoor lighting technologies from traditional light sources to light emitting diodes (LED). LEDs emit broad-spectrum white light, with a significant amount of photosynthetically active radiation, and typically a high content of blue light that regulates circadian rhythms in many organisms...
May 14, 2018: Environmental Pollution
Rachael Al-Saadon, Christopher Sutton, Weitao Yang
Thermally activated delayed florescence (TADF) is a mechanism that increases the electroluminescence efficiency in organic light-emitting diodes by harnessing both singlet and triplet excitons. TADF is facilitated by a small energy difference between the first singlet (S1 ) and triplet (T1 ) excited states (ΔE(ST)), which is minimized by spatial separation of the donor and acceptor moieties. The resultant charge-transfer (CT) excited states are difficult to model using time-dependent density functional theory (TDDFT) because of the delocalization error present in standard density functional approximations to the exchange-correlation energy...
May 17, 2018: Journal of Chemical Theory and Computation
Andrew J Clark, Paul Yang, Khizer R Khaderi, Andrew A Moshfeghi
Electronic displays have become an integral part of life in the developed world since the revolution of mobile computing a decade ago. With the release of multiple consumer-grade virtual reality (VR) and augmented reality (AR) products in the past 2 years utilizing head-mounted displays (HMDs), as well as the development of low-cost, smartphone-based HMDs, the ability to intimately interact with electronic screens is greater than ever. VR/AR HMDs also place the display at much closer ocular proximity than traditional electronic devices while also isolating the user from the ambient environment to create a "closed" system between the user's eyes and the display...
May 1, 2018: Ophthalmic Surgery, Lasers & Imaging Retina
Rong Wang, Donglian Zhang, You Xiong, Xuehong Zhou, Cao Liu, Weifeng Chen, Weijing Wu, Lei Zhou, Miao Xu, Lei Wang, Linlin Liu, Junbiao Peng, Yuguang Ma, Yong Cao
The thin-film transistor (TFT) driving circuit is a separate electronic component embedded within the panel itself to switch the current for each pixel in active-matrix organic light-emitting diode displays. We reported a TFT-directed dye electroplating method to fabricate pixels; this would be a new method to deposit films on prepatterned electrode for organic full-color display, where TFT driving circuit provide a switching current signal to drive and direct dye depositing on selected RGB pixels. A prototype patterned color pixel matrix was achieved, as high-quality light-emitting films with uniform morphology, pure RGB chromaticity, and stable output...
May 18, 2018: ACS Applied Materials & Interfaces
Irish Valerie B Maggay, Wei-Ren Liu
Ba3Y(BO3)3:Eu3+, Bi3+ were successfully prepared via a solid-state reaction. The crystallinity, photoluminescence properties, energy transfer and thermal quenching properties were studied. Subjecting Ba3Y(BO3)3:Bi3+ samples to different excitation wavelengths (340-370 nm), obtained blue and green emission ascribed to Bi3+(II) and Bi3+(I) sites, respectively. The influence of these two sites were systematically investigated. Bi3+ efficiently transferred its absorbed energy to neighboring Eu3+ sites by enhancing its luminescence intensity...
January 1, 2018: Journal of Nanoscience and Nanotechnology
Philipp Strobel, Christian Maak, Volker Weiler, Peter J Schmidt, Wolfgang Schnick
Highly efficient phosphor-converted light-emitting diodes (pc-LEDs) are popular in lighting and high-tech electronics applications. The main goals of present LED research are increasing light quality, preserving color point stability and reducing energy consumption. For those purposes excellent phosphors in all spectral regions are required. Here, we report on ultra-narrow band blue emitting oxoberyllates AELi2[Be4O6]:Eu2+ (AE = Sr,Ba) exhibiting a rigid covalent network isotypic to the nitridoalumosilicate BaLi2[(Al2Si2)N6]:Eu2+...
May 16, 2018: Angewandte Chemie
Robert Naumann, Florian Lehmann, Martin Goez
We have explored alkyl substitution of the ligands as a means to improve the performance of the title complexes in photoredox catalytic systems that produce synthetically useable amounts of hydrated electrons through photon pooling. Despite generating a superreductant, these electron sources only consume the bioavailable ascorbate and are driven by a green light-emitting diode (LED). The substitutions influence the catalyst activity through the quenching and recombination rates across the micelle-water interface, and the photoionization quantum yield...
May 16, 2018: Chemistry: a European Journal
Valentina J Alaasam, Richard Duncan, Stefania Casagrande, Scott Davies, Abhijaat Sidher, Brett Seymoure, Yantao Shen, Yong Zhang, Jenny Q Ouyang
Nighttime light pollution is quickly becoming a pervasive, global concern. Since the invention and proliferation of light-emitting diodes (LED), it has become common for consumers to select from a range of color temperatures of light with varying spectra. Yet, the biological impacts of these different spectra on organisms remain unclear. We tested if nighttime illumination of LEDs, at two commercially available color temperatures (3000 and 5000 K) and at ecologically relevant illumination levels affected body condition, food intake, locomotor activity, and glucocorticoid levels in zebra finches (Taeniopygia guttata)...
May 15, 2018: Journal of Experimental Zoology. Part A, Ecological and Integrative Physiology
Jin-Hyeon Yun, Alexander Y Polyakov, Kyu-Cheol Kim, Yeon Tae Yu, Donghyun Lee, In-Hwan Lee
We propose stretchable plasmonic templates of Au and Au/SiO2 nanoparticles (NPs) to improve the luminescence of CsPbBr3 perovskite nanocrystals (PNCs). These templates are highly flexible and consist of polymer-metal NP composites that facilitate the luminescence enhancement by localized surface plasmons (LSPs) due to coupling with metal NP. This template also prevents the degradation of carrier transport properties for perovskite light-emitting diodes by embedding metal NPs in polymer. The luminescence of PNC film on the template with Au NPs decreases by 21% compared to PNC films on the reference (polymer film without metal NPs), while it increases by 54% for the templates with Au/SiO2 NPs...
May 15, 2018: Optics Letters
Miguel Lastra-Mejías, Albertina Torreblanca-Zanca, Regina Aroca-Santos, John C Cancilla, Jesús G Izquierdo, José S Torrecilla
A set of 10 honeys comprising a diverse range of botanical origins have been successfully characterized through fluorescence spectroscopy using inexpensive light-emitting diodes (LEDs) as light sources. It has been proven that each LED-honey combination tested originates a unique emission spectrum, which enables the authentication of every honey, being able to correctly label it with its botanical origin. Furthermore, the analysis was backed up by a mathematical analysis based on partial least square models which led to a correct classification rate of each type of honey of over 95%...
August 1, 2018: Talanta
Tae-Ho Kwon, Jai-Eun Kim, Ki-Doo Kim
In the field of communication, synchronization is always an important issue. The communication between a light-emitting diode (LED) array (LEA) and a camera is known as visual multiple-input multiple-output (MIMO), for which the data transmitter and receiver must be synchronized for seamless communication. In visual-MIMO, LEDs generally have a faster data rate than the camera. Hence, we propose an effective time-sharing-based synchronization technique with its color-independent characteristics providing the key to overcome this synchronization problem in visual-MIMO communication...
May 14, 2018: Sensors
Ioannis Lignos, Viktoriia Morad, Yevhen Shynkarenko, Caterina Bernasconi, Richard M Maceiczyk, Loredana Protesescu, Federica Bertolotti, Sudhir Kumar, Stefan T Ochsenbein, Norberto Masciocchi, Antonietta Guagliardi, Chih-Jen Shih, Maryna I Bodnarchuk, Andrew J deMello, Maksym V Kovalenko
Hybrid organic-inorganic and fully inorganic lead halide perovskite nanocrystals (NCs) have recently emerged as versatile solution-processable light-emitting and light-harvesting optoelectronic materials. A particularly difficult challenge lies in warranting the practical utility of such semiconductor NCs in the red and infrared spectral regions. In this context, all three archetypal A-site monocationic perovskites-CH3NH3PbI3, CH(NH2)2PbI3, and CsPbI3-suffer from either chemical or thermodynamic instabilities in their bulk form...
May 12, 2018: ACS Nano
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