PBD的掺杂对PVK:Ir(ppy)3体系发光特性的影响

从三线态激子的发光机理入手,研究了PBD作为电子传输材料对PVK:Ir(ppy)3体系的影响。实验中制备了单层器件ITO/PVK:Ir(ppy)3/PBD/Al,ITO/PVK:Ir(ppy)3:PBD/Al和双层器件,ITO/PVK:Ir(ppy)3:PBD/BCP/Al,其中PVK:Ir(ppy)3的掺杂浓度比例不变,通过改变PBD的掺杂浓度,其变化范围是PBD与PVK的质量比从0:100到20:100,制得了一系列器件,研究了它们的光致发光(PL)光谱和电致发光(EL)光谱。发现PBD这种电子传输材料的加入对器件的亮度有很大提高,当PBD与PVK质量比为10%时,器件亮度最大。     

PBD在稀土配合物与PVK混合体系电致发光中的作用

研究了PBD以较低浓度与铽配合物[Tb(m-MBA)₃phen]₂·2H₂O、PVK共掺杂体系的电致发光,制作了两类电致发光器件：ITO/PVK:Tb complex/PBD/LiF/Al,ITO/PVK：Tb complex:PBD/PBD/LiF/Al。在共掺杂的发光层中铽配合物的电致发光来源于两个途径,一个是由PVK到铽配合物的能量传递,另一个是电子和空穴在铽配合物上直接复合发光。改变PBD在发光层中的掺杂比例,制得一系列器件,通过对其光谱和亮度的研究,发现PBD在较低浓度掺杂时器件的稳定性和亮度随掺杂浓度的增加而降低。通过分析认为PBD的加入对给体(PVK)到受体(Tb complex)的能量传递效率影响较小,主要是由于PBD的加入使得电子和空穴在PVK链间的跳跃受到限制,使在由PVK、铽配合物和PBD三者掺杂组成的发光层中,注入的电子和空穴不能有效地在铽配合物上复合,这样就会减少激子在铽配合物上直接复合的概率,而造成器件的亮度和效率降低。     

Improved electron injection of OLEDs with a thin PBD layer at Alq3/Cs2CO3 interface

In this study, the effect of one oxadiazole derivative (PBD) using as an electron injection layer (EIL) at Alq₃/Cs₂CO₃ interface has been investigated. The present of PBD EIL was showed an interesting enhanced electron injection for OLEDs although the nominal electron injection barrier for PBD based OLEDs is much larger, because PBD owns an obvious higher intrinsic the Lowest Unoccupied Molecular Orbital level (2.3 eV) than that of Alq₃ (3.0 eV). For example, the current density of OLEDs at 8 V was increased from 54 mA/cm² to 168 mA/cm² when inserting a thin PBD layer (5 nm) at Alq₃/Cs₂CO₃ interface. Here the increased current is suggested associating with the changed electronic structure of PBD when it contacts with Cs₂CO₃.     

有机量子阱的光学性质

采用多源有机分子气相沉积系统(OMBD)制备了Alq₃，PBD/Alq₃，PBD/Alq₃/PBD单层、双层以及量子阱结构，利用电化学循环伏安法和吸收光谱、荧光光谱研究了量子阱的类型和样品的光致发光特性.电化学循环伏安法和吸收光谱的测量结果表明，PBD/Alq₃有机量子阱为Ⅰ型量子阱结构.荧光光谱的研究结果表明，单层Alq₃的光致发光峰不随Alq₃厚度变化而变化；但是双层PBD/Alq₃结构光致发光峰随Alq₃厚度的减小而发生蓝移；同样对于PBD/Alq₃/PBD量子阱结构光致发光峰随Alq₃厚度的减小而发生蓝移.对引起光谱蓝移的原因进行了讨论. 关键词： 有机量子阱 光谱蓝移     

Ir（PPY）3对Rubrene荧光材料的敏化性研究

最近几年,磷光器件是有机电致发光研究领域和产业化的一大热点。在实验中作者发现PVK∶PBD∶Rubrene共掺体系的发光中存在较强的PVK发光,能量传递不充分。由于一些具有重金属离子的有机物,存在强的自旋-轨道耦合作用,引入到共掺体系可以充分利用单线态和三线态的发光,从而获得高于一般有机材料器件所达到的内量子效率。为获得单色性较好的Rubrene发光,作者将磷光敏化剂Ir(ppy)3引入到PVK∶PBD∶Rubrene共掺溶液中,得到了纯正Rubrene发光,Forester能量传递也更加充分。当进一步提高Rubrene掺杂浓度以后,单色性Rubrene发光更加明显,并讨论了Ir(ppy)3所起的作用和器件的发光机理。磷光材料与有机小分子材料共掺的方法,可以有效提高器件的发光亮度及效率。     

电子传输层PBD对Alq3：DCJTB电致发光器件的影响

以PBD为电子传输层制作了一组掺杂型有机电致发光器件,并研究了掺杂器件中PBD对器件的光谱、亮度等的影响。发现PBD与NPB和DCJTB分别掺杂的器件的光谱与其它的器件不同,然后运用了载流子的注入、传输及PBD的传输特性等方法对光谱做出了合理的解释,并运用高斯截谱的方法分析了各个发光峰的产生原因。     

有机多层量子阱结构的光致发光特性的研究

采用多源高真空有机分子束沉积系统(OMBDs),将两种有机小分子材料PBD和Alq₃以交替生长的方式,制备了不同厚度的PBD/Alq₃有机多层量子阱结构(OMQWs), 并利用电化学循环伏安法和光吸收分别测定了PBD和Alq₃的最低空分子轨道(LUMO)和最高占据分子轨道(HOMO)。该结构类似于无机半导体中的Ⅰ型量子阱结构,PBD层作为势垒层,Alq3层作为势阱层和发光层,并进行了小角X射线衍射(XRD)的测量。利用荧光光谱研究了OMQWs光致发光(PL)特性,得到随着阱层厚度的降低,光致发光的峰位将蓝移;同时随垒层厚度的减小,PBD的发光峰逐渐消失。利用量子阱结构可以使PBD的能量有效的传递给Alq₃,从而增强Alq₃的发光。     

The effect of driving voltage on the electroluminescent property of a blend of poly(9-vinylcarbazole) and 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole

The impact of driving voltage on the electroluminescence (EL) from organic light emitting diode with ITO/PVK:PBD:TBAPF₆(10:10:1)/Al structure was analyzed by the method of Gaussian fitting. Indium tin oxide (ITO) was used as anode, poly(9-vinylcarbazole) (PVK) as polymeric host, 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole (PBD) as electron-transporting molecule, tetrabutylammonium hexafluorophosphate (TBAPF₆) as organic salt and aluminium (Al) as cathode. A broad EL has been observed and it could be attributed to the overlap of emission from four different excited state complexes, including PVK:PBD exciplex, PVK:PBD electroplex, PBD electromer and PVK electromer. The EL spectra shifted to longer wavelength with the increase of driving voltage. The ratio of PVK electromer to PVK:PBD exciplex emission intensity first declined slightly and then increased remarkably, while the relative intensity of combination of PVK:PBD electroplex and PBD electromer emission remained unchanged when the voltage was increased.     

多层有机薄膜电致发光器件

制备了以苯乙烯锘三苯胺衍生物为空穴传输层Ａｌｑ３为发光层的双层有机薄膜电致姨光器件。还把不同厚度的恶二唑衍生物加在ＳＡ和Ａｌｑ３之间制备了两种三层结构的有机薄膜电致发光器件，实现了ＳＡ的蓝色发光。进行了器件存放实验，发现了器件在大气中有较好的稳定性。     

混合发光层有机电致发光器件中的多重成分发射

以等摩尔空穴传输材料TPD和电子传输材料PBD组成结构为ITO/TPD/TPD∶PBD/PBD/Al的混合物发光层有机电致发光(EL)器件,观察到了相对于组成材料的荧光光谱红移的宽发射带。通过比较EL光谱,光致发光光谱及EL光谱分解,表明电致发光中同时包含单体发射、激基复合物和电荷对复合物的发射。激基复合物为TPD的激发态TPD*与PBD的基态相互作用形成TPD*PBD类型的复合物,电荷对复合物是带电荷的空穴传输分子(D+)的空穴和电子传输分子(A-)的电子交叉复合而形成的(D+-A-)*复合物。各激发态在电场作用下呈现不同的形成机理和复合过程,并且单体发射和激发态复合物的比例随电场而变化,导致发射光谱随电场增强而蓝移。该器件的最高亮度和最大外部量子效率分别为240 cd·(cm2)-1和0.49%。有机固态界面激基复合物或电荷对复合物的发射常出现宽的红移发射带,是调节发光颜色的有效手段。     

DNA dynamics - Experiment proposals

We argue that a breather wave, describing DNA dynamics, behaves like a real soliton. We rely on a Peyrard-Bishop-Dauxois (PBD) model. In addition, we propose a couple of experiments to confirm or reject this statement. These experiments should study solitonic interactions using micromanipulation technique. Also, we suggest how to measure a solitonic width and its amplitude.     

PBD分子对聚合物发光二极管特性的影响

研究了由聚合物发光材料poly(2-methoxy,5-(2-ethy lhexyloxy)-1,4-phenyleneviny lene)(MEH-PPV)掺杂2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole(PBD)制成的发光层厚度为80,170nm的高分子发光器件(PLEDs)。研究了PBD不同掺杂浓度时器件的电流密度-电压(J-V)和亮度-效率-电压(L-E-V)特性,发现PBD除传输电子外,还阻挡空穴的注入和传输。研究发现,PBD的最优掺杂浓度为20%,掺入PBD后MEH-PPV的EL光谱红移且发生窄化,当PBD掺杂浓度为40%时MEH-PPV的EL光谱窄化最明显,EL光谱半峰全宽从100nm减小到44nm。     

Influence of heterojunction interface on exciplex emission from organic light-emitting diodes under electric fields

In this paper, electroluminescence from organic light-emitting diodes based on 2-(4^′-biphenyl)-5-(4^′′-tert-butylphenyl)-1,3,4-oxadiazole (PBD) and N,N^′-diphenyl-N,N^′-bis(3-methylphenyl)-(1,1^′-biphenyl)-4,4^′-diamine (TPD) is reported. Based on the exciplex emission from the TPD/PBD interface under high electric fields, the influence of the TPD/PBD interface on exciplex emission was investigated by increasing the number of TPD/PBD interfaces while keeping both the total thickness of the TPD layer and the PBD layer constant in the multiple quantum-wells (MQW) device ITO/TPD/[PBD/TPD]_n/PBD/Al (n is the well number that was varied from 0 to 3). Our experimental data shows that exciplex emission can be enhanced by suitably increasing the well number of this kind of MQW-like device. PACS 78.60.Fi; 78.55.Kz; 73.61.Ph     

An MRI Analysis of the Dissolution of a Soluble Drug Incorporated within an Insoluble Polymer Tablet

Magnetic resonance imaging is used to map the ingress of water into a nominally nonswelling polymer-matrix slow-release drug delivery device comprising a compact of particulate Eudragit polymer and Diltiazem Hydrochloride drug. It is shown that the water ingresses with the square root of time: that is, it is "Fickian-like"; and that the release depends only weakly on the particulate size. A dissolution–diffusion model specifically incorporating the drug particulate size is developed to describe the release mechanism. The experimental results are in accord with the model. It is further shown theoretically that the release should become "non-Fickian-like" and particle size dependent if the drug dissolution constant were to be reduced substantially, an observation explained using a dimensionless scaling argument that compares the dissolution and diffusion rates. It has, however, not been possible to perform experiments in this different regime with the same materials. Authors' address: Peter J. McDonald, Department of Physics, School of Electronics and Physical Sciences, University of Surrey, Guildford, GU2 7XH, UK     

Photophysical characterizations of 2-(4-biphenylyl)-5 phenyl-1,3,4-oxadiazole in restricted geometry

Langmuir and Langmuir-Blodgett (LB) films of non-amphiphilic 2-(4-Biphenylyl)-5-phenyl-1,3,4-oxadiazole (abbreviated as PBD) mixed with stearic acid (SA) as well as with the inert polymer matrix poly(methyl methacrylate) (PMMA) have been studied. Surface pressure versus area per molecule (π-A) isotherm studies suggest that PBD molecules very likely stand vertically on the air-water interface and this arrangement allows the PBD molecules to form stacks and remain sandwiched between SA/PMMA molecules. At lower surface pressure, phase separation between PBD and matrix molecules occurs due to repulsive interaction. However, at higher surface pressure, PBD molecules form aggregates. The UV-vis absorption and steady-state fluorescence spectroscopic studies of the mixed LB films of PBD reveal the nature of the aggregates. H-type aggregate predominates in the mixed LB films, whereas I-type aggregate predominates in the PBD-PMMA spin-coated films. The degree of deformation produced in the electronic levels are largely affected by the film thickness and the surface pressure of lifting.     

Dispersive infrared photothermal beam deflection spectroscopy

A single-beam dispersive photothermal beam deflection (PBD) spectrometer system usable in the IR range is described. A Nernst glower along with a severely modified Perkin-Elmer Model 421 monochromator were used to illuminate a solid sample with modulated monochromatic IR radiation. The resulting photothermal effect generated at the sample's surface caused modulated changes in the refractive index of the air over the sample, causing a probe laser beam grazing the surface to be deflected. The deflections were measured with a bi-cell silicon photodetector. Experiments and analysis of the deflection system showed that lenses used to focus the probe beam at the sample were not needed, and that an improvement in the PBD signal could be obtained by increasing the sample-to-detector distance, but only until a certain sample-detector separation was attained. The dispersive PBD instrument is less sensitive than one based on an interferometer but can be profitably used for studies requiring control of the modulation frequency. Useful spectra of solids were recorded over the 4000-550 cm⁻¹ region using IR excitation in the approximately 5 × 10⁻⁶−5 × 10⁻⁷W range.     

Efficient and low potential operative host/guest concentration graded bilayer polymer electrophosphorescence devices

This study investigates enhanced electrophosphorescence and its mechanism in poly(N-vinyl carbazole) (PVK): N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1-biphenyl]-4,4′-diamine (TPD)/2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD): fac-tris(2-phenylpyridine)iridium [Ir(ppy)₃] concentration graded bilayer electroluminescence devices. The two layers are partially intermixed at the bilayer interface because the upper layer (composed of Ir(ppy)₃ and PBD) was spun cast from a solvent that slightly swells the bottom layer (composed of PVK and TPD). Moreover, PBD in the upper layer can act as an efficient electron transport layer as well as a hole blocking layer, resulting in greatly enhanced electron–hole recombination. An indium tin oxide (ITO)/3,4-polyethylenedioxythiophene–polystyrenesulfonate (PEDOT)/[PVK:TPD/Ir(ppy)₃:PBD] bilayer/LiF/Al device showed dramatically decreased turn-on and driving voltages, enhanced luminescence efficiency, and narrower emission spectra compared to those of conventional ITO/PEDOT:PSS/[PVK:TPD:Ir(ppy)₃:PBD] blend/LiF/Al devices.     

双层有机电致发光器件中多成分激发态发射

在结构为ITO/TPD(60nm)/PBD(60nm)/Al的双层器件观察到了单体发射、激基复合物发射和电荷对复合物发射.该器件和TPD∶PBD(等摩尔)混合蒸发薄膜的光致发光光谱研究表明激基复合物仅在TPD/PBD界面形成.电致发光光谱随偏置变化，反映出各激发态的不同形成机理和不同的占有比例及载流子在器件中动态复合的过程. 关键词： 电致发光 激发态发射 激基复合物 电荷对复合物     

A meshless method based on moving Kriging interpolation for a two-dimensional time-fractional diffusion equation

Fractional diffusion equations have been the focus of modeling problems in hydrology, biology, viscoelasticity, physics, engineering, and other areas of applications. In this paper, a meshfree method based on the moving Kriging inter- polation is developed for a two-dimensional time-fractional diffusion equation. The shape function and its derivatives are obtained by the moving Kriging interpolation technique. For possessing the Kronecker delta property, this technique is very efficient in imposing the essential boundary conditions. The governing time-fractional diffusion equations are transformed into a standard weak formulation by the Galerkin method. It is then discretized into a meshfree system of time-dependent equations, which are solved by the standard central difference method. Numerical examples illustrating the applicability and effectiveness of the proposed method are presented and discussed in detail.