Time-resolved photoluminescence study on concentration quenching of a red emitting tetraphenylchlorin dye for organic electroluminescent devices

Time-resolved photoluminescence (PL) of a red emitting dye, tetraphenylchlorin (TPC), doped in poly(methylmethacrylate) (PMMA) at various concentrations was studied to clarify the mechanism of concentration quenching often observed in organic electroluminescence devices. At doping concentrations lower than 10⁻² mol/L, PL lifetimes of TPC were relatively constant (∼10 ns) and equal to that of TPC in dilute solution. At doping concentrations higher than 10⁻² mol/L, PL lifetime decreased rapidly with increasing concentration, down to 2 ns at 8 × 10⁻² mol/L. This decrease in PL lifetime was related to the concentration quenching of TPC monomer emission by the increasing number of TPC dimer sites formed at such higher concentrations. Our experimental results of concentration-dependence trapping agree fairly well with the theoretical model of trapping by dimers reported in literature.     

A novel white organic electroluminescent device based on a thin LiF interlayer

A novel white organic electroluminescent device was fabricated by inserting a thin lithium fluoride (LiF) layer in the emitting layer (tris-(8-hydroxyquinoline) aluminum (Alq₃)). The electroluminescence device with the configuration indium tin oxide (ITO)/N,N′-diphenyl-N,N′-bis(l-napthyl)-1,1′-biphenyl-4,4′-diamine (NPB; 45 nm)/tris-(8-hydroxyquinoline) aluminum (Alq₃; x nm)/LiF (0.3 nm)/Alq₃ ((45 − x) nm)/Al (150 nm) showed expanded electroluminescence (EL) spectra. The spectra contain tricolor, so this should be a simple method to realize white light emitting. We also elucidated the mechanism of expanded EL spectra formation and investigated the properties of these devices.     

Photophysical properties and electroluminescent applications of donor–acceptor–donor functionalized red electroactive fluorescent materials

Four electroactive molecular materials with donor-π-acceptor-π-donor structures have been synthesized for investigation of structure–properties relationships, and used as dopant for electroluminescent applications. The optical and electrical properties of these materials are electronically manipulated by attaching different donors. The twisted intramolecular charge transfer (TICT) model is proposed by photophysical behaviors observed with increasing solvent polarity. Red electroluminescence devices were fabricated by spin coating the blend of polymer host and fluorescent guest. Highly efficient energy transfer leads to a saturated red emission with emission peak at 623 nm, narrow bandwidth of 75 nm and an external quantum efficiency of 0.38%.     

Highly efficient energy transfer to a novel organic dye in OLED devices

The neutral 4,4-difluoro-8-(2,2′:6′,2″-terpyridine-4′-yl)-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (Boditerpy) molecule was synthesized and incorporated as dopant (<1%) in double-layer organic light emitting diodes (OLEDs) with the configuration ITO/α-NPD(60 nm)/Alq₃(60 nm):Boditerpy (0.4 nm)/LiF(0.02 nm)/Al(80 nm). This device exhibits green emission with a brightness of 545 cd/m² at 8 V and a maximum power efficiency of 0.9 lm/W. A full quantitative energy transfer process is indicated by a complete quenching of light emission from Alq₃ in photoluminescence. However, I–V characteristics indicate some losses during the charge transfer processes in OLED configuration     

Synthesis,photoluminescent and electroluminescent properties of a novel europium(III) complex involving both hole- and electron-transporting functional groups

A novel europium(III) complex involving a carbazole fragment as hole-transporting group and an oxadiazole fragment as electron-transporting group was synthesized and used as red light-emitting material in organic light-emitting diodes (OLEDs). The complex is amorphous, and exhibits high glass transition temperature (T_g = 157 °C) and high thermal stability with a 5% weight loss temperature of 367 °C. Two devices, device 1: ITO/NPB (40 nm)/Eu(III) complex (30 nm)/Alq₃ (30 nm)/LiF (1 nm)/Al (100 nm) and device 2: ITO/NPB (40 nm)/3% Eu(III) complex: CBP (30 nm)/BCP (10 nm)/Alq₃ (30 nm)/LiF (1 nm)/Al (100 nm), were fabricated, where NPB is N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine, Alq₃ is tris(8-hydroxyquinoline) Al(III), CBP is 4,4′-bis(carbazole-9-yl)-biphenyl, and BCP is 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, respectively. In contrast with device 1, owing to less self-quenching and better charge confinement, device 2 shows improved performances: the maximum luminance of device 2 was dramatically increased from 199 to 1845 cd/m², the maximum current efficiency was increased from 0.69 to 2.62 cd/A, the turn-on voltage was decreased from 9.5 to 5.5 V, and higher color purity was attained.     

Synthesis,photophysical and electroluminescent properties of a novel bright light-emitting Eu3+ complex based on a fluorene-containing bidentate aryl phosphine oxide

A novel bidentate aryl phosphine oxide (APO) ligand with fluorene as the chromophore (9,9-diethyl-9H-fluorene-2,7-diyl)bis(diphenylphosphine)oxide (EFDPO), as well as the corresponding Eu³⁺ complex 1 were designed and synthesized. The strong absorption antennae effect of the functional APO ligands was proved. The effect of EFDPO in the intramolecular singlet and triplet energy transfer was also investigated. It is showed that the rigid structure and the appropriate energy levels of EFDPO not only reduce the energy loss induced by the structure relaxation, but also restrain the solvent quenching and facilitate the energy transfer from EFDPO to Eu³⁺. The thermal analysis was also performed to prove the improved thermal stability and phase stability of the complex. The complex exhibited good electroluminescent (EL) performance, such as maximum brightness more than 600 cd m^?2, E.Q.E. around 2% and stable monochromic red emission at 616 nm.     

The electroluminescent and photodiode device made of a polymer blend

Organic thin film diodes made by a polymer blend of poly[2-methoxy,5-(2'-ethyl-hexoxy)-1.4-phenylenevinylene] (MEH-PPV) and poly[1.3-propanedioxy-1.4-phenylene-1,2-ethenylene-(2.5-bis(trimethylsilyl)-1,4-phenylene)-1,2-ethenylene-1,4-phenylene] (called the B-polymer) are investigated. The device of sandwich configuration indium-tin oxide (ITO)/polymer-blend/A1 emits orange light under forward bias at + 10 V and the same device acts as a photodiode under reverse bias. To investigate the photodiode characteristics, the 516 nm wavelength with 9.5 mW/cm² intensity of light is illuminated through the A1 contact side of the device. The I-V characteristic measurement shows the short circuit current and the open circuit voltage of −1.22 × 10⁻⁹ A/cm² and 0.8 V, respectively. The ratio of the photocurrent to the dark current is about 4 × 10² at − 2.5 V reverse bias. The maximum d.c. sensitivity is 1.35 × 10 −⁵ A/W at 4× 7 V reverse bias voltage with 16 mW/cm² intensity of the incident light. The results indicate the possibility of making photosensors using this device.     

Design and synthesis of a novel class of inhibitors for mild steel corrosion in acidic and carbon dioxide-saturated saline media

p-(9-(2-Methylisoxazolidin-5-yl)nonyloxy)benzaldehyde I, prepared using a cycloaddition protocol, was elaborated into its cinnamaldehyde derivative II which upon quarternization with propargyl chloride afforded III bearing an interesting blend of structural traits suitable for imparting inhibition of mild steel corrosion. Novel compounds I–III showed efficient inhibition against mild steel corrosion in CO₂–0.5 M NaCl (40 °C, 1 atm; 120 °C, 10 bar), 1, 4, 7.7 M HCl, and 0.5 M H₂SO₄ at 60 °C as determined by gravimetry and electrochemical methods. The presence of carbonaceous surface and nitrogen, as revealed by XPS study, indicated the formation of a film covering the metal surface, which imparted corrosion inhibition.     

Triphenylamine- and oxadiazole-substituted poly(1,4-phenylenevinylene)s: synthesis,photo-, and electroluminescent properties

Novel triphenylamine- and oxadiazole-substituted poly(1,4-phenylenevinylene)s (PPV) or CN-PPV (P1–4) were synthesized by the Wittig–Horner, Knoevenagel, and Gilch type polymerization. The polymers exhibited good solubility in common organic solvents, relatively high photoluminescent (PL) efficiency, and high HOMO level for ca. −5.1 eV. The simple double-layer devices of triphenylamine-PPV (P1), ITO/PEDOT: PSS/P1/Cs/Al, exhibited a very high luminance of 510 cd/m² under a low driving voltage of 3 V, demonstrating the effectiveness of triphenylamine moiety as a substituent of PPV derivatives for a light-emitting polymer. Triphenylamine-CN-PPV (P2) exhibited bipolar reversible redox in CV. The bipolar type of PPVs, P2 and triphenylamine-oxadiazole-PPV (P3), showed lower luminance and efficiency than those of the p-type of PPV (P1).     

A novel route to synthesis of photoluminescent dye/polypyrrole nanoparticles: Effects of intermolecular energy transfer on nucleation and growth of polypyrrole

Photoluminescent dye/polypyrrole nanoparticles were prepared by one-step polymerization of pyrrole monomer in the presence of the dye molecules under UV light illumination. Oxygen in the air was selected as an oxidant in this method. Optical properties of the nanoparticles were investigated, revealing that the nanoparticles exhibited higher photostability than pure RhB. In addition, it was found that the presence of both dye molecules and UV light played the important role in the formation of the nanoparticles. And then the mechanism for the formation of well-confined nanoparticles was explained via the effects of intermolecular energy transfer between the dye molecules and pyrrole monomer on nucleation and growth of polypyrrole.     

水热法制备新型TiO_2薄膜及其机理

用酞酸丁酯和盐酸通过两步水热法制备了一种新型双层Ti O2薄膜。其水热过程包括生长过程和刻蚀过程。在生长过程制备了一种上层为纳米棒团簇,下层为纳米棒阵列的双层结构。在随后的刻蚀过程中,上层的纳米棒团簇转变为纳米管团簇,下层的纳米棒阵列转变为直径在20~25 nm的纳米线阵列。刻蚀过程上下两层出现不同形貌的主要原因为金红石相Ti O2的各向异性以及纳米棒外壁和内部的不同界面能。新型薄膜作为染料敏化太阳能电池的光阳极时能量转换效率高。     

Conformational phase transition in a high-efficiency near-ultraviolet electroluminescent diarylpolysilane

We report on the observation of a structural phase transition in a diarylpolysilane, poly[bis(p-n-butylphenyl)silane] (PBPS), which was recently shown to emit high-efficiency room-temperature electroluminescence (EL) in the near-ultraviolet region. Spectroscopic and calorimetric experiments have revealed that this structural phase transition accompanies a conformational change in the Si-backbones of PBPS from the disorder form (lower temperature form) to the trans-planar form (higher temperature form). The spectroscopic changes induced by this structural phase transition are discussed in relation to the EL characteristics of PBPS, and found to have positive effects on them.     

Electron transport and electroluminescent efficiency of conjugated polymers

The relation between charge balance and electroluminescent efficiency for polymers is studied systematically in this work. Light-emitting diodes of several kinds of polymers with very different efficiency are compared. The electron and hole currents are measured in the uni-polar devices and fitted by the theoretical model to get carrier mobilities. The universal features of the high efficiency polymers are that the electron and hole mobilities are comparable and the electron current is larger than the hole current due to the higher hole barriers. The electron current is more crucial than hole current to determine the efficiency in the bipolar light-emitting diode. The purity of polymers and low electron injection barriers both play significant roles in producing stronger electron currents. These results give the physical rules for designing new polymers and the device structures to achieve highly electroluminescent devices.     

赤泥沉降用聚丙烯酰胺的合成及应用

采用均相水溶液聚合法,新型水溶性偶氮引发剂M合成了用于赤泥沉降的聚丙烯酰胺絮凝剂.通过大量实验确定了合成的优化条件为:单体浓度为25%;引发剂浓度为单体质量的0.01%;引发温度30℃;介质pH值为6;EDTA -2Na用量为15mg/L;甲酸钠用量为350μg/L.该条件下制得的聚丙烯酰胺分子量可达2000万.通过赤泥沉降实验测试了絮凝性能,相对分子质量为1200万自制絮凝剂NP2用量为30g/t-干赤泥时,沉降速度为13.5m/h.优于Nalco9779,但澄清度不及Nalco9779.     

Blue light electroluminescent devices based on a copolymer derived from fluorene and carbazole

Thin layers of poly(dihexylfluorene-co-N-hexylcarbazole) (poly(DHF-co-NHK) sandwiched between indium tin oxide (ITO) and aluminium electrodes show stable photoluminescence (PL) and electroluminescence (EL) at room temperature and ambient atmosphere. I(V) and EL vs. voltage curves present a much lower threshold than device made up of poly(DHF) homopolymer. The behaviour of both materials has been quantitatively investigated through a Fowler–Nordheim analysis allowing the determination of the energy offsets between the Fermi level of the ITO electrode and the HOMO of polymers. When using the copolymer, the barrier height for hole injection is reduced to a value close to 0.17 eV compared to 0.83 eV for the homopolymer. This difference in offsets has been confirmed by electrochemical investigations.     

一种新型直流弧焊系统设计

针对直流弧焊发电机存在耗电大、耗材多、噪声大、控制精度不高等问题,提出了一种新型的拓扑电路代替传统的直流弧焊发电机,该拓扑电路由不控整流后的电压再经过DC/DC变换器得到焊接直流电压和直流电流.分析了半桥式隔离DC/DC变换主电路和控制部分的PWM波的产生和系统的保护措施.详细介绍了参数的计算方法,并通过实验验证了电路...     

A new organic/inorganic electroluminescent material with a silsesquioxane core

This paper describes a new polyhedral oligomeric silsesquioxane (POSS)-based blue-light electroluminescent nanoparticle, octakis[N-(9-ethyl-9H-carbazol-3-yl)undecanamide-11-dimethylsiloxy]silsesquioxane (POSS-C11-Cz), which contains eight carbazole chromophore arms, synthesized through the hydrosilation reaction of octakis(dimethylsiloxy)silsesquioxane with the terminal olefin Cz-C11ene. POSS-C11-Cz exhibits good thermal and electrochemical stabilities and good film-forming properties. The optical and photoluminescence spectra of POSS-C11-Cz in solution and in the solid state indicate a reduction in the degrees of aggregation and excimer formation because inter-chain interactions were prohibited by the bulky POSS core. Moreover, photoluminescence spectra of a POSS-C11-Cz (3 wt.%)/polyfluorene (97 wt.%) blend revealed that the color was stable after heating the sample at 200 °C for 5 h; in contrast, the pure polyfluorene exhibited a significant green emission at 530 nm. A triple-layer device based on this blend exhibited higher maximum brightness and luminance efficiencies relative to those of the pure polyfluorene. Thus, the organic/inorganic POSS-C11-Cz/polyfluorene blend has potential for use in polymeric light-emitting diodes because of its improved thermal and optoelectronic characteristics.     

新奇的双帽Keggin型磷钒铬杂多化合物的水热合成与表征

在水热条件下合成了一种以低价过渡金属元素铬取代的高钒杂多化合物K13 PV12 Cr2 O4 2 ·2 1.2H2 O ,并用元素分析、X射线衍射、红外光谱、紫外可见光谱以及X射线光电子能谱和热重分析等手段对其进行了表征。结果表明 ,该杂多化合物具有新奇的双帽Keggin型结构 ,而两个低价的Cr(Ⅲ )原子可能取代了K9PV14 O4 2 中处于极位的两个帽上的V(Ⅴ )原子 ,这种取代可能导致该杂多化合物具有较好的催化性能。     

Photo-oxidation of polymers used in electroluminescent devices

Two electroluminescent polymers, poly(2,5-bis(cholestanoxy)-1,4-phenylene vinylene) (BCHA-PPV) and poly(3-octylthiophene) (P3OT), have been characterized on Au and Al substrates in terms of photo-oxidative stability after exposure to UV and visible irradiation from a Hg lamp. Thin polymer films were analyzed in situ using IR reflection absorption spectroscopy (IRRAS), and ex situ by X-ray photoelectron spectroscopy (XPS) and attenuated total reflection (ATR) IR spectroscopy. The oxidation of BCHA-PPV is quite extensive, resulting in the formation of an ester and volatile aldehyde species. Singlet oxygen, formed by energy transfer from the BCHA-PPV triplet state, appears responsible for at least one photo-oxidation pathway. BCHA-PPV triplet exciton states will also form during electroluminescent device operation (the singlet exciton state is responsible for luminescence in the film) resulting in the formation of reactive singlet oxygen. Thus, it appears that BCHA-PPV will slowly self-degrade in the presence of oxygen when used as the active layer in electroluminescent devices. P3OT shows no detectable oxidation during similar exposure.     

A novel red phosphor for white light emitting diodes

A novel red phosphor, CaMoO₄:Eu³⁺, has been developed for white light emitting diodes (LEDs). The phosphor was prepared by using oxides in air and its luminescent properties have been investigated. The excitation and emission spectra indicate that this phosphor can be effectively excited by ultraviolet (UV) (394 nm) and blue (464 nm) light, and exhibits a satisfactory red performance (616 nm), nicely fitting in with the widely applied UV or blue LED chips. The novel phosphor is much more stable and has stronger emission intensity than the sulfide red phosphors used in white LEDs.