Preparation of 8-hydroxyquinoline wires by decomposition of tris(8-hydroxyquinoline) aluminium

We fabricated 8-hydroxyquinoline (HQ) wires by two methods, decomposition of tris(HQ) aluminium at low pressure in a tube furnace and heating of HQ powder at atmospheric pressure. Fabricated wires were crystalline, and exhibited the same optical properties (absorption and photoluminescence) as HQ powder. While the properties of wires prepared by two different methods were the same, it should be noted that synthesis by decomposition of tris(HQ) aluminium required elimination of mechanical vibration of the growth tube. Implications of decomposition of tris(HQ) aluminium during organic vapour phase deposition growth on organic optoelectronic device performance are discussed.     

Hole Spin Polarization in Metallic Ferromagnetic GaMnAs Multilayers and Superlattices: Lateral and Bloch Miniband Transport

It is shown that spin-polarized currents occur in metallic and ferromagnetic Ga_1–x Mn _x As/GaAs multilayered structures, as a result of the magnetic interaction between holes and the Mn ions. The magnetic layers act as potential barriers for holes with spins aligned parallel to the layer magnetization, and as potential wells for the inverse spin polarization. In the case of currents in-plane, holes with spin parallel and antiparallel to this magnetization move in different regions. By choosing properly the magnetic and the nonmagnetic layers widths, a spin-polarized transport with a difference of an order of magnitude on the mobilities for each spin polarization is predicted to occur. Spin-polarized minibands are also shown to occur in a superlattice based on the same structure. We calculated the dependence of the spin polarization with the superlattice parameters, and we discuss how this polarization affects the Bloch miniband transport in such ferromagnetic superlattice.     

8-羟基喹啉铝表面包覆SiO2的研究

以有机电致发光材料-8-羟基喹啉铝(Alq3)为研究对象,在其表面包覆SiO2来改善有机电致发光器件中的材料界面,从而延长器件寿命.利用透射电子显微镜、光致发光光谱、热重分析分别对产物的形貌、发光性能和热稳定性进行了表征,借助扫描电镜和X射线光电子能谱仪对产物的薄膜进行了微观分析,分别以Alq3和包覆了SiO2的Alq...     

一种制备8-羟基喹啉铝的新方法

用一种简单、高效的方法合成了8-羟基喹啉铝.通过核磁共振谱和紫外光谱,证明了铝参与了配位和8-羟基喹啉铝的存在.对得到的晶体进行X-射线晶体结构分析,其主要晶胞参数为单胞尺寸a=1.11882nm,b=1.32614nm,c=1.6701nm,β=94.011(10)°.V=2.4718nm3,Z=4,计算密度1.358mg/m3,吸收系数0.124 mm-1.在氯仿溶液中对Alq进行了单光子荧光测试,其发射峰在520nm处,对以Alq为电子传输层的器件进行性能测试,其EL最大发射峰在516nm,起始电压为3.0V,15V时的亮度为19458cd/m2.最大流明效率和最大电流效率分别为0.70lm/W和1.32cd/A.     

Growth and characterization of tris(8-hydroxyquinoline)-aluminum molecular films

Various tris(8-hydroxyquinoline)-aluminum (Alq3) molecular solid films were grown on top of indium-tin-oxide (ITO) glass substrates using physical vapor deposition. The effect of changing the growth conditions on the properties of the films was studied. From scanning electron microscopy, an Alq3 planar layer over an ITO-substrate was observed at the initial period, and an Alq3 tubular structure (which becomes dominant at substrate temperature T_sub ≧ 90 °C) was found to nucleate from this layer. From X-ray diffraction, the Alq3 planar layer possesses an amorphous character while the Alq3 tubular layer has a triclinic α-phase structure. Based on an Arrhenius plot of the growth rate versus 1/T_sub, the growth behaviors in various T_sub-regions were discussed to be dominated by adhesion (for T_sub < 90 °C), steric effect (90 °C < T_sub < 150 °C), and re-evaporation (T_sub > 150 °C). Then, from optical transmission and photoluminescence spectra performed on the high crystalline Alq3 films, two signals associated with the optical-bandgap E_g absorption and the gap-state absorption were determined and discussed in terms of the optical properties of the constituent Alq3 molecules. Finally, from a fit of E_g(T) by an effective electron-phonon interaction model, the physical significance of these fitting parameters for the Alq3 molecular solid was investigated.     

Effect of Ca and buffer layers on the performance of organic light-emitting diodes based on tris-(8-hydroxyquinoline) aluminum

The effects of buffer layers, including LiF, LiCl, NaF, NaCl, NaI, KI, RbF, RbCl, CsF, CsCl, MgF₂, CaF₂, BaF₂, and BaCl₂ on electron injection and device performance in organic light-emitting diodes based on tris-(8-hydroxyquinoline) aluminum, were investigated systematically. The insertion of the buffer layers at the organic/cathode interface not only reduced the operating voltage, but also enhanced the luminance and efficiency, which is attributed to the improvement of electron injection efficiency. It was found that the efficiency of the electron injection was closely related to the inherent properties of the buffer layer, such as its melting point (MP) and dielectric constant (ε), as well as with the buffer layer's interface with the metallic electrode through the effective work function (WF). Low MP, low ε and low WF values result in an effective improvement in the injection of the electrons, and thus to the device performance. The electroluminescent performance was further improved by the introduction of calcium between the buffer layer and the aluminum electrode.     

Photoconductivity of a bundle of Bis(8-hydroxyquinoline) cadmium nanoribbons

Large-scale Bis(8-hydroxyquinoline) cadmium nanoribbons were obtained by a facile solvothermal method. The as-prepared products were characterized with X-ray diffraction, Fourier transform infrared and scanning electron microscopy, which reveals uniform Bis(8-hydroxyquinoline) cadmium nanoribbons with width of 400 nm and thickness of 120 nm. A photoconduction device was fabricated based on nanoribbons and the photoconductive properties were studied. As the light source was switched on and off, the currents could be reversibly switched between high and low value at the voltage of 0.01 V. The result was interesting and might be found potential application in photoswitch devices.     

Ordered growth and local workfunction measurements of tris(8-hydroxyquinoline) aluminium on ultrathin KBr films

In this work we investigate the growth of tris(8-hydroxyquinoline) aluminium (Alq(3)) on single-crystal Ag(111) substrates partially covered by an ultrathin KBr film. Noncontact atomic force microscopy is used to determine the molecular ordering of 0.8 monolayer Alq(3) evaporated onto these substrates. The simultaneous measurement of the local surface potential by means of Kelvin probe force microscopy yields the local workfunction difference between the pure Ag(111) surface and the one covered by an ultrathin KBr film, by pure Alq(3), or by both (KBr|Alq(3)). The molecular ordering and the interface dipole formation are discussed with respect to experiments described in the literature in which electron diffraction and photoelectron spectroscopy were used, respectively.     

Synthesis and electroluminescence properties of zinc(2,2′ bipyridine)8-hydroxyquinoline

New electroluminescent material, namely zinc(2,2′ bipyridine)8-hydroxyquinoline [Zn(Bpy)q] has been synthesized and characterized. A solution of Zn(Bpy)q showed absorption maxima at 382 nm and 342 nm in toluene solution attributed to π − π transition. The photoluminescence spectrum in toluene solution showed peak at 545 nm. The material was stable up to 350 °C. Organic light emitting diode (OLED) fabricated with the structure ITO/α-NPD/Zn(Bpy)q/Alq₃/LiF/Al exhibits a broad electroluminescence peak at 548 nm. The maximum current efficiency of OLED was 1.34 cd/A at 5 V and the maximum power efficiency 0.84 lm/W at 5 V.     

Fabrication and electrogenerated chemiluminescence properties of uniform octahedral 8-hydroxyquinoline zinc (Znq2)

Well-defined octahedral Znq₂ has been synthesized via a facile solvothermal route. Field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) images show that the as-prepared product has an octahedral structure with an edge length of 2 μm. The reaction parameters, such as solvent, reaction time and temperature, play an important part in the morphology of the final product. A possible formation mechanism for octahedral Znq₂ is proposed. The as-prepared octahedral Znq₂ exhibits excellent electrogenerated chemiluminescence (ECL) behaviour.     

Electrical Electron Spin Injection with a p+-(Ga,Mn)As/n+-GaAs Tunnel Junction

We demonstrate electrical electron spin injection in a p⁺-(Ga,Mn)As/n⁺-GaAs tunnel junction with an n-GaAs/(In,Ga)As/p-GaAs light emitting diode (LED). By applying a reverse bias to the p⁺-(Ga,Mn)As/n⁺-GaAs junction (forward bias to the LED), we observed clear hysteresis in electroluminescence (EL) polarization. The magnitude of the EL polarization, which does not depend critically on the spacer layer thickness up to 800 nm, is found to be about five times greater than that of the hole spin injection.     

纳米ZnO掺杂对ZrO2(8mol% Y2O3稳定)电性能的影响研究

采用纳米粉料,在单轴成型,无压烧结条件下,用交流阻抗谱技术对掺不同质量百分比ZnO的ZrO2(8mol% Y2O3稳定)烧结体的电性能进行了研究.研究发现ZnO掺杂对ZrO2(8mol% Y2O3稳定)的离子导电性能具有优化作用.     

三(8-羟基喹啉)铝(Alq3)发光性能的调控

三(8-羟基喹啉)铝(Alq3)是有机电致发光器件的基础材料.本文评述了如何通过分子的化学修饰和聚集态结构的改变来调控其发光光谱,提高发光效率.这将为开发高性能的有机电致发光材料及器件提供参考与依据.     

Structure, charge-transfer and luminescent properties bis(2-methyl-8-hydroxyquinoline) gallium chloride

Bis(2-methyl-8-hydroxyquinoline) Gallium Chloride (GaMq2Cl) has been synthesized and characterized by X-ray crystallography. It is known from X-ray diffraction data on single crystals that the crystals of GaMq2Cl were monoclinic, space group C2/c, a = 28.701 A, b = 9.5405 A, c = 15.1434 A, Z = 8. Its thermal stability, electron structures and structural stability were investigated by TG analysis and quantum chemical calculations. The complex was a thermally stable material, with decomposition temperature being 348 degrees C. The electron-transfer property of GaMq2Cl is of advantage over hole-transfer property. Under UV excitation at 365 nm, the complex emits blue fluorescence with the maximum emission peak at 471 nm. Finally, blue-green light-emitting devices using this complex as the emissive layer were also fabricated and investigated, with emission wavelength at 502 nm. The results promote GaMq2Cl as a good candidate for luminescent material.     

8-羟基喹啉锌/碳微球复合材料的合成表征及发光性能

利用流变相反应法制备了碳微球(CMSs)负载8-羟基喹啉锌(Znq2)的复合材料.通过场发射扫描电子显微镜、X射线衍射仪、热重分析仪、X射线光电子能谱仪、傅里叶红外光谱仪和荧光分光光度计等对Znq2/CMSs复合材料结构和发光性能进行了表征和分析.结果表明:Znq2以非共价键形式负载于直径均匀的CMSs(300～400...     

Organometallic tris(8-hydroxyquinoline)aluminum complexes as buffer layers and dopants in inverted organic solar cells

Tris(8-hydroxyquinoline)aluminum (Alq₃) is a frequently used material for organic light emitting diodes. The electronic properties and solubility can be tuned by chemical tailoring of the quinoline part, which makes it an interesting candidate for organic solar cells. Steady-state absorption and fluorescence, as well as time-resolved fluorescence properties of the parent Alq₃ and a series of complexes consisting of derivatives, such as 4-substituted pyrazol, methylpyrazol, arylvinyl, and pyridinoanthrene moieties, of the quinoline ligand, were studied in solutions and in thin films. Suitability of the complexes as anodic buffer layers or dopants in inverted organic solar cells based on the well known bulk heterojunction of poly(3-hexylthiophene) (P3HT) and phenyl-C₆₁-butyric acid methyl ester (PCBM) was tested. The devices equipped with the derivatives showed higher power conversion efficiency (η) compared to the photocells containing the parent Alq₃. Open circuit voltage (V_oc) was increased when the derivatives were utilized as the anodic buffer layer. Doping of the P3HT:PCBM with a small amount of Alq₃ or its derivative improved short circuit current density, V_oc, fill factor, and η, while the series resistance decreased. In addition, the devices were stable in air over several weeks without encapsulation. Possible mechanisms leading to the improvements in the photovoltaic performance by using the parent Alq₃ or its derivative as buffer layer or dopant are discussed.     

A facile route to ultra-long bis(8-hydroxyquinoline) magnesium nanoribbons and the fabrication of photoswitch

Large-scale and high-purity bis(8-hydroxyquinoline) magnesium nanoribbons with an average width of 125 nm, a thickness of 25 nm, and a length up to several hundreds of micrometers, were synthesized via a facile solvothermal route. The room-temperature photoluminescence spectrum of the products showed a strong and stable blue-green emission centered at 482 nm under excitation at 378 nm. And the as-prepared nanoribbons exhibited linear current-voltage characteristics and excellent photoresponse. As the light source was switched on and off, the currents could be reversibly switched between high and low values at a voltage of 0.1 V, which might be useful in the fabrication of photosensor and photoswitch microdevices or nanodevices in the future.     

Temperature-independent electron tunneling injection in tris (8-hydroxyquinoline) aluminum thin film from high-work-function gold electrode

We fabricated electron-only tris (8-hydroxyquinoline) aluminum (Alq₃) single-layer devices with a device structure of glass substrate/MgAg anode (100 nm)/Alq₃ layer (100 nm)/metal cathode (100 nm), and systematically varied the work functions (WF) of the metal cathodes from WF = − 1.9 (Cs) to − 2.9 (Ca), − 3.8 (Mg), − 4.4 (Al), − 4.6 (Ag), and − 5.2 eV (Au) to investigate how electron injection barriers at the cathode/Alq₃ interfaces influence their current density–voltage (J–V) characteristics. We found that current densities at a certain driving voltage decrease and the temperature dependence of J–V characteristics of the devices gradually becomes weaker as the work functions of the metal cathodes are decreased. The device with the highest-work-function Au cathode exhibited virtually temperature-independent J–V characteristics, suggesting that a current flow mechanism of this device is mainly controlled by electron tunneling injection at the Au/Alq₃ interface.     

Effect of the ligand on the properties of emitting materials: Pentacoordinated 8-hydroxyquinoline aluminum complexes

Two series of pentacoordinated complexes, AlMq₂q′ and Alq₂q′ (q is 8-hydroxyquinoline, Mq is 2-methyl-8-hydroxyquinoline and q′ is phenolato ligand), were synthesized, and assessed as potential emitting materials in thin film (photoluminescence, PL) and electroluminescent (EL) device. EL devices with a configuration of ITO/NPB(50 nm)/Complex(50 nm)/Mg/Ag(10:1) were fabricated. Strong blue and green emission were observed from thin solid film and EL device of AlMq₂q′ and Alq₂q′, respectively. The results revealed that the PL and EL emission wavelengths of these materials are primarily determined by Mq and q (first ligand), whereas phenolato ligand (second ligand) has little effect on the emission wavelength but remarkable influence on EL efficiency.