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Driving Voltage (driving + voltage)
Selected AbstractsGrowth and characterization of near stoichiometric LiNbO3 single crystalCRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2007S. H. Yao Abstract A near stoichiometric LiNbO3 single crystal has been grown by the Czochralski method from a 58.5% Li melt hold in a large platinum crucible. High resolution X-ray rocking curves of 300 and 0006 reflections indicated that the near stoichiometric LiNbO3 crystal possesses the high structural quality. Compared with the congruent LiNbO3, the near stoichiometric LiNbO3 possesses shorter ultraviolet absorption edge, thus higher Li concentration. The OH, infrared absorption band analyses showed that the Li concentration in the near stoichiometric LiNbO3 crystal is higher than that in the congruent LiNbO3 crystal. This result is in good agreement with that of the ultraviolet absorption edge. The electro-optic (EO) coefficient ,22 of the near stoichiometric LiNbO3 crystal was measured to be 6.75 pm/V higher than that of congruent LiNbO3 crystal. It also proves the near stoichiometric LiNbO3 electro-optic Q-switched requires a low driving voltage and it is advantageous for the device performance. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Numerical modeling of the Joule heating effect on electrokinetic flow focusingELECTROPHORESIS, Issue 10 2006Kuan-Da Huang Abstract In electrokinetically driven microfluidic systems, the driving voltage applied during operation tends to induce a Joule heating effect in the buffer solution. This heat source alters the solution's characteristics and changes both the electrical potential field and the velocity field during the transport process. This study performs a series of numerical simulations to investigate the Joule heating effect and analyzes its influence on the electrokinetic focusing performance. The results indicate that the Joule heating effect causes the diffusion coefficient of the sample to increase, the potential distribution to change, and the flow velocity field to adopt a nonuniform profile. These variations are particularly pronounced under tighter focusing conditions and at higher applied electrical intensities. In numerical investigations, it is found that the focused bandwidth broadens because thermal diffusion effect is enhanced by Joule heating. The variation in the potential distribution induces a nonuniform flow field and causes the focused bandwidth to tighten and broaden alternately as a result of the convex and concave velocity flow profiles, respectively. The present results confirm that the Joule heating effect exerts a considerable influence on the electrokinetic focusing ratio. [source] Doping of the Metal Oxide Nanostructure and its Influence in Organic ElectronicsADVANCED FUNCTIONAL MATERIALS, Issue 8 2009Mi-Hyae Park Abstract Synthesizing metal oxides through the sol,gel process provides a convenient way for forming a nanostructured layer in wide band gap semiconductors. In this paper, a unique method of introducing dopants into the metal oxide semiconductor is presented. The doped TiO2 is prepared by adding a Cs2CO3 solution to a nanocrystalline TiO2 solution that is synthesized via a non-hydrolytic sol,gel process. The properties of the TiO2:Cs layer are investigated and the results show stable nanostructure morphology. In addition to providing morphological stability, Cs in TiO2 also gives rise to a more desirable work function for charge transport in organic electronics. Polymer solar cells based on the poly(3-hexylthiophene) (P3HT): methanofullerene (PC70BM) system with the addition of a TiO2:Cs interfacial layer exhibit excellent characteristics with a power conversion efficiency of up to 4.2%. The improved device performance is attributed to an improved polymer/metal contact, more efficient electron extraction, and better hole blocking properties. The effectiveness of this unique functionality also extends to polymer light emitting devices, where a lower driving voltage, improved efficiency, and extended lifetime are demonstrated. [source] Rational Color Tuning and Luminescent Properties of Functionalized Boron-Containing 2-Pyridyl Pyrrolide Complexes,ADVANCED FUNCTIONAL MATERIALS, Issue 4 2005H.-Y. Chen Abstract Three systematically functionalized pyrrolide ligands were prepared via the coupling of methyl vinyl ketone and the respective carbaldehyde reagents, followed by treatment of the pre-formed dicarbonyl compounds with (NH4)2CO3 in order to generate the required pyrrole fragment. These ligands readily reacted with the boron reagent BPh3 to afford the complexes [(pyro)BPh2] (2a), [(noro)BPh2] (2b), and [(xaro)BPh2] (2c), where (pyro)H, (noro)H, and (xaro)H represents the 2-pyridyl, 2-quinolinyl, and 2-quinoxalinyl pyrrole groups, respectively. Complexes 2a,2c give stable solutions in air, and show strong photoluminescence with emission peak maxima located at 490,nm, 510,nm, and 575,nm, respectively. Calculations based upon time-dependent density function theory (TDDFT) show that the S1 state in these complexes is attributed to an allowed (,-symmetry),,,,* (,-symmetry) transition located at the chelating pyrrolide moieties. Electroluminescence (EL) devices based on 2c were fabricated. The EL emission from 2c as the host-emitter, with the emission peak maximum shifted to 580,nm, was observed when BCP was used as the hole blocking material. This device produces saturated red-orange light-emission at an onset voltage of 8,V and a maximum brightness of 5000,cd,m,2 at a driving voltage of 15,V; the external quantum yield is estimated to be 0.5,%. [source] Resonant Tunneling Processes along Conjugated Molecular Wires: A Quantum-Chemical DescriptionADVANCED FUNCTIONAL MATERIALS, Issue 11-12 2002Y. Karzazi Abstract Molecular electronics research is a very active area in the field of nanotechnology. It is now well established that individual or self-assembled molecules can behave as nanoscopic switches in transistor and diode configurations. Molecular wires inserted into nanopores and contacted by two metallic electrodes can also be used as active elements for the fabrication of resonant tunneling diodes (RTDs). The RTD current/voltage (I/V) characteristics can display a negative differential resistance (NDR) behavior (i.e., a negative slope in the I/V curve) for reasons that are not yet fully understood. Here we describe a possible mechanism at the quantum-chemical level that is based on conformational effects and accounts for the experimental observation of strong NDR signatures in substituted phenylene ethynylene oligomers. The occurrence of a peak current in the I/V curves is rationalized by analyzing the evolution of the one-electron structure of the molecular wires upon application of a static electric field aligned along the molecular axis (the field simulates the driving voltage applied between the two electrodes in the RTD devices). The results of our calculations provide a general basis to develop strategies for the design of molecular wires displaying an NDR behavior. [source] Low-Driving-Voltage Electroluminescence in Perovskite FilmsADVANCED MATERIALS, Issue 36 2009Hiroshi Takashima Perovskite thin-film electroluminescence devices are prepared, opening up a new optical application of perovskite materials. With increasing driving voltage, the intensity of electroluminescence increases dramatically. High-quality red color is produced and the working voltage for whole-surface electroluminescence is as low as 10 V. [source] Actuating Single Wall Carbon Nanotube,Polymer Composites: Intrinsic Unimorphs,ADVANCED MATERIALS, Issue 11 2008Cheol Park A novel actuating single wall carbon nanotube (SWNT)/polymer composite is reported. It exhibits a large strain (2.6%) at a low driving voltage (<1 MV m,1) while possessing excellent mechanical and thermal properties. The strain energy density is at least an order of magnitude greater than any state-of-the-art polymeric materials reported. The actuating characteristic mainly originates from the electrostrictive contribution, presumably due to interfacial polarization. [source] An investigation into the morphology and electro-optical properties of 2-hydroxy ethyl methacrylate polymer dispersed liquid crystalsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2010Huey-Ling Chang Abstract Polymer dispersed liquid crystal (PDLC) films are fabricated using E7 liquid crystals, tetraethylene glycol diacrylate (TeGDA) crosslinking agent, and 0,66.49 mol % 2-hydroxy ethyl methacrylate (HEMA). The effects of different levels of HEMA addition on the microstructure and electro-optical properties of the PDLC samples are examined using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and UV-Vis spectroscopy, respectively. The results show that the refractive index of the PDLC films is insensitive to the level of HEMA addition. However, an increasing HEMA content improves the degree of phase separation during the polymerization process and increases the size and uniformity of the liquid crystal domain. As a result, the electro-optical properties of the PDLC films are significantly improved as the level of HEMA addition is increased. Overall, the results show that a PDLC comprising 40 wt % E7 liquid crystals, 33.51 mol % TeGDA and 66.49 mol % HEMA has a high contrast ratio (13 : 1) and a low driving voltage (10 V) and is therefore an ideal candidate for a wide variety of intelligent photoelectric applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] White electroluminescence from a single polyfluorene containing bis-DCM unitsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2007Sang Kyu Lee Abstract A series of fluorene-based copolymers composed of blue- and orange-light-emitting comonomers were synthesized through palladium-catalyzed Suzuki coupling reactions. 9,9-Dihexylfluorene and 2-(2,6-bis-{2-[1-(9,9-dihexyl-9H -fluoren-2-yl)-1,2,3,4-tetrahydroquinolin-6-yl]-vinyl}-pyran-4-ylidene)-malononitrile (DCMF) were used as the blue- and orange-light-emitting chromophores, respectively. The resulting single polymers exhibited simultaneous blue (423/450 nm) and orange (580,600 nm) emissions from these two chromophores. By adjusting the fluorene and DCMF contents, white light emission could be obtained from a single polymer; a device with an ITO/PEDOT:PSS/polymer/Ca/Al configuration was found to exhibit pure white electroluminescence with Commission Internationale de L'Eclairage (CIE) coordinates of (0.33, 0.31), a maximum brightness of 1180 cd/m2, and a current efficiency of 0.60 cd/A. Furthermore, the white light emission of this device was found to be very stable with respect to variation of the driving voltage. The CIE coordinates of the device were (0.32, 0.29), (0.32, 0.29), and (0.33, 0.31) for driving voltages of 7, 8, and 10 V, respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3380,3390, 2007 [source] Design and Synthesis of Phosphorescent Iridium Containing Dendrimers for Potential Applications in Organic Light-Emitting Diodes,MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 18 2008Qin-De Liu Abstract Three phosphorescent dendrimers (IrC1, IrC3, and IrF2) with an iridium complex core and oligocarbazole or oligofluorene substituted ligands were synthesized and characterized. The structures of the oligocarbazole were designed to maintain high triplet energy of the ligands so that phosphorescence quenching in the resulting dendrimers can be prevented, while the oligofluorene in IrF2 resulted in undesired phosphorescence quenching. Best performance was obtained from an IrC3 based electrophosphorescent light-emitting device with a maximum luminance of 13,060 cd,·,m,2 at a driving voltage of 11.5 V and a peak current-efficiency of 4.3 cd,·,A,1 at a luminance of 3,400 cd,·,m,2, owing to its high PL efficiency, and efficient energy transfer between the iridium complex core and the ligands. [source] White light generation through yellow nanophosphor and blue organic light-emitting diodePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2009Je Hong Park Abstract White light-emitting device (WLED) combining yellow-emitting nanophosphor and blue organic light-emitting diode (LED) was developed. WLED was fabricated by using a spin-coating method. Yellow-emitting nanophosphor was dispersed in the blue-emitting polymer solution for spin-coating. As a variation of mixture ratio of yellow-emitting nanophosphor and blue-emitting polymer in emitting layer, the emission spectra were studied. Our white organic light-emitting device with 30% phosphor mixture ratio and at the driving voltage of 17 V showed the color coordinates of x = 0.266 and y = 0.33. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Substituent Effect To Prevent Autoxidation and Improve Spectral Stability in Blue Light-Emitting PolyfluorenesCHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2005Jiu Yan Li Dr. Abstract A group of fluorene-based polymers, PF-1SOR and PF-2SOR, were synthesized and characterized as blue light-emitting materials. PF-1SOR and PF-2SOR displayed nematic liquid crystalline mesophase in films cast from solution. Compared with conventional polyfluorene, PF-1SOR and PF-2SOR display blue-shifted UV absorption and structureless blue fluorescence. The photoluminescence spectra of PF-1SOR and PF-2SOR were found insensitive against thermal treatment in air up to 200°,C and the blue electroluminescence in their light-emitting devices was independent of the driving voltage. Compared to the conventional polyfluorenes, the improved spectral stability of these polymers is attributed to the anti-oxidization effect of (3,5-di(tert -butyl)phenoxy)sulfonyl side groups attached to the backbone. [source] Structure,Property Relationship of Pyridine-Containing Triphenyl Benzene Electron-Transport Materials for Highly Efficient Blue Phosphorescent OLEDsADVANCED FUNCTIONAL MATERIALS, Issue 8 2009Shi-Jian Su Abstract Three triphenyl benzene derivatives of 1,3,5-tri(m -pyrid-2-yl-phenyl)benzene (Tm2PyPB), 1,3,5-tri(m -pyrid-3-yl-phenyl)benzene (Tm3PyPB) and 1,3,5-tri(m -pyrid-4-yl-phenyl)benzene (Tm4PyPB), containing pyridine rings at the periphery, are developed as electron-transport and hole/exciton-blocking materials for iridium(III) bis(4,6-(di-fluorophenyl)pyridinato- N,C2,)picolinate (FIrpic)-based blue phosphorescent organic light-emitting devices. Their highest occupied molecular orbital and lowest unoccupied molecular orbital (LUMO) energy levels decrease as the nitrogen atom of the pyridine ring moves from position 2 to 3 and 4; this is supported by both experimental results and density functional theory calculations, and gives improved electron-injection and hole-blocking properties. They exhibit a high electron mobility of 10,4,10,3,cm2,V,1,s,1 and a high triplet energy level of 2.75,eV. Confinement of FIrpic triplet excitons is strongly dependent on the nitrogen atom position of the pyridine ring. The second exponential decay component in the transient photoluminescence decays of Firpic-doped films also decreases when the position of the nitrogen atom in the pyridine ring changes. Reduced driving voltages are obtained when the nitrogen atom position changes because of improved electron injection as a result of the reduced LUMO level, but a better carrier balance is achieved for the Tm3PyPB-based device. An external quantum efficiency (EQE) over 93% of maximum EQE was achieved for the Tm4PyPB-based device at an illumination-relevant luminance of 1000,cd,m,2, indicating reduced efficiency roll-off due to better confinement of FIrpic triplet excitons by Tm4PyPB in contrast to Tm2PyPB and Tm3PyPB. [source] High-Efficiency White-Light Emission from a Single Copolymer: Fluorescent Blue, Green, and Red Chromophores on a Conjugated Polymer Backbone,ADVANCED MATERIALS, Issue 8 2007J. Luo The synthesis and properties of a single copolymer incorporating well-separated blue, green, and red chromophores on a single conjugated polymer backbone are reported. This copolymer is shown to have CIE coordinates of (0.35,0.34) and a luminance efficiency of 6.2,cd,A,1. The color coordinates of the resulting white-light emission remained extremely stable over a wide range of driving voltages. [source] Synthesis and white electroluminescent properties of multicomponent copolymers containing polyfluorene, oligo(phenylenevinylene), and porphyrin derivativesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2009Hui Li Abstract Two novel multicomponent copolymers (P1 and P2) containing polyfluorene (PF), oligo(phenylenevinylene) (OPV), and porphyrin (Por) derivatives were synthesized according to the Suzuki polymerization method. The structures, optical, and electrochemical properties of the two model compounds (OPV and Por) and multicomponent copolymers were characterized by 1H NMR, FTIR, elemental analysis, UV,vis spectroscopy, photoluminescence, and cyclic voltammetry, respectively. Both of the copolymers exhibit thermotropic liquid crystalline properties and represent the characteristic Schlieren textures in a wide temperature range. Electroluminescence spectra of these copolymers exhibit broadband emissions covering the entire visible region from 400 to 700 nm. The single layer polymer light emitting diodes device based on P2 with a configuration of indium tin oxide/poly(ethylenedioxythiophene):poly(styrenesulfonic acid)/polymers/Ca/Al emits white light with the Commission Internationale de l,Eclairage chromaticity coordinates of (0.29, 0.30), maximum brightness of 443 cd/m2. The white-light-emitting devices based on the novel multicomponent copolymers exhibit low turn-on voltage, and good color stability at different driving voltages as well. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5291,5303, 2009 [source] | |||||||||||||||||||||||||