Fabrication of blue top-emitting organic light-emitting devices with highly saturated color

Blue top-emitting organic light-emitting devices (TOLEDs) with highly saturated color were developed by microcavity effect. The device structure studied was glass/reflective silver/indium-tin oxide (ITO)/organic electroluminescent stack/semi-transparent cathode (calcium/silver). By changing the thicknesses of ITO and organic layers in the microcavity structure device doped with p-bis(p-N, N-di-phenyl-aminostyryl)benzene (DSA-ph), highly saturated color with Commission Internationale de L'Eclairage chromaticity coordinates (CIE_x,y) of (0.14, 0.08) was obtained.     

White light emitting diodes (LEDs) with good color rendering indices (CRI) and high luminous efficiencies by the encapsulation of mixed and double-deck phosphors

In this paper, white light emitting diodes (LEDs) with good color rendering indices (CRI) and high luminous efficiencies have been fabricated by the encapsulation of mixed and double-deck phosphors. Experimental results revealed that white LEDs with the encapsulation of double-deck phosphors exhibited better CRI and higher luminous efficiencies than those with the encapsulation of mixed phosphors because no secondary excitation took place. The hue, CRI, and luminous efficiencies of white LEDs with double-deck phosphors under 200 mA were CIE_x,y = (0.357, 0.348), 90, and 62.3 lm/W, respectively while the hue, CRI, and luminous efficiencies of white LEDs with mixed phosphors under 200 mA were CIE_x,y = (0.366, 0.354), 89, and 56.5 lm/W, respectively.     

A study on the characteristics of OLEDs using Ir complex for blue phosphorescence

Several iridium-based complexes were investigated as phosphorescent dopants. They achieved about 100% internal quantum efficiency, due to utilization of both singlet and triplet excitons in the radiative processes. We have fabricated phosphorescent OLEDs with 8% Ir(ppz)₃ as a triplet emissive dopant in various host materials. CBP, which has an efficiency of 0.20 cd/A, is the best host material. Furthermore, we synthesized metal-organic phosphor complexes based on Ir with different ligands as to (Im)₂Ir(acac), (Im-R)₂Ir(acac), and Ir(ppz)₂(acac).     

Efficient and color-saturated inverted bottom-emitting organic light-emitting devices with a semi-transparent metal-assisted electron injection layer

We report the development of highly efficient and color-saturated green fluorescent 10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-benzo[l]pyrano-[6,7,8-ij]quinolizin-11-one dye-doped inverted bottom-emitting organic light-emitting diode (IBOLED). This was enabled by the insertion of a silver (Ag) based semi-transparent metal-assisted electron injection layer between the ITO cathode and n-doped electron transporting layer. This IBOLED with ITO/Ag bilayer cathode with its synergistic microcavity effect achieved luminous efficiencies of 20.7 cd/A and 12.4 lm/W and a saturated CIE_x,y of (0.22, 0.72) at 20 mA/cm², which are twice better than those of the conventional OLED and have over 60% improvement on IBOLED without ITO/Ag bilayer cathode.     

Composition dependent self‐regenerative property of perovskite‐type oxides

The self‐regenerative property of LaCo_{1–x –y}Pd_x Zn_y O_3±δ and LaFe_{1–x –y}Pd_x Zn_y O_3±δ solid solutions with monometallic Pd or bimetallic Pd/Zn substituents for Co or Fe is studied under a redox cycle by high angular annular dark‐field scanning transmission electron microscopy (STEM‐HAADF) and energy dispersive X‐ray spectroscopy (EDX) and X‐ray diffraction (XRD). These results reveal that the composition of perovskites determines the self‐regenerative property that occurs largely in LaCo_{1–x –y}Pd_x Zn_y O_3±δ but is limited greatly in LaFe_{1–x –y}Pd_x Zn_y O_3±δ. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Thermal stability of amorphous SiOC/crystalline Fe composite

We examined the thermal stability of amorphous silicon oxycarbide (SiOC) and crystalline Fe composite by in situ and ex situ annealing. The Fe/SiOC multilayer thin films were grown via magnetron sputtering with controlled length scales on a surface-oxidized Si (100) substrate. These Fe/SiOC multilayers were in situ or ex situ annealed at temperature of 600 °C or lower. The thin multilayer sample (~10 nm) was observed to have a layer breakdown after 600 °C annealing. Diffusion starts from low groove angle triple junctions in Fe layers. In contrast, the thick multilayer structure (~70 nm) was found to be stable and an intermixed layer (Fe_xSi_yO_z) was observed after 600 °C annealing. The thickness of the intermixed layer does not vary as annealing time goes up. The results suggest that the Fe_xSi_yO_z layer can impede further Fe, Si and O diffusion, and assists in maintaining morphological stability.     

Theoretical investigations of the EPR g factors and the local structures for Ni3+ in LiAlyCo1–yO2 at various Al concentrations

The electron paramagnetic resonance (EPR) g factors and local structures for Ni³⁺ in LiAl_yCo_1–yO₂ as the cathode materials for lithium-ion batteries are theoretically investigated at various Al concentrations y (= 0.1, 0.5, 0.8 and 1.0). The [NiO₆]^9– clusters are subject to the tetragonal elongation distortions along the C₄ axis owing to the Jahn–Teller effect and the different degrees of distortions are characterised by the slightly increasing relative elongation ratio ρ (and also crystal-field strength and covalency) with y. In pure LiAlO₂ (y = 1.0), the [NiO₆]^9– cluster exhibits the largest ρ (≈1.4%) and an additional relative variation ratio τ (≈1.4%) of the planar bond lengths, responsible for the perpendicular g anisotropy δg = (g_x – g_y). The number of impurity Ni³⁺ centres increases from one at y = 0 and 1.0 to two at y = 0.1 and 0.8 and reaches the maximum four at y = 0.5, in accordance with the increasing degree of disorder of the systems. The distinct impurity centres for the same y may be accompanied by the comparable energies of the ground and near excited states, similar to ‘resonant states’ with slightly different local elongation distortions and tetragonal level splittings. The present studies will be helpful to understand the relationships between local structures and performances of LiAl_yCo_1–yO₂ type cathode materials.     

高效、色度稳定的顶发射白光有机发光二极管

顶发射白光有机发光二极管(white organic light-emitting diodes,WOLEDs)因可与有源驱动电路结合实现大开口率和高分辨率,因而在白光照明和全彩显示中有着良好的应用前景．本文制备了红/蓝双磷光发光层的顶发射WOLEDs,通过在红光层与蓝光层间插入电子阻挡层tris(phenypyrazole)iridium(Ir(ppz)₃),降低了对红光掺杂浓度的要求,红光掺杂浓度的提高不仅降低了对制备工艺的要求,提高了工艺可重复性,而且改善了WOLEDs的效率与色度稳定性。分析了色度稳定的原因,优化了红光和蓝光磷光客体的掺杂浓度,制备出发光效率达到7.9 cd·A-1的顶发射WOLED,其色坐标位于暖白光区,在87～2 402 cd·m-2亮度范围内色度很稳定,仅变化(0.006,0.01)。     

基于ZnS增透膜的顶发射白光有机发光二极管

顶发射白光有机发光二极管(TEWOLED)在白光照明和全彩显示中有着良好的应用前景, 克服顶发射器件中的微腔效应是制备光电性能良好的TEWOLED的前提. 使用具有高折射率的ZnS作为增透膜改善金属阴极在蓝光波段的透射率,降低其反射性, 从而有效抑制了微腔的影响.同时利用转移矩阵理论和宽角干涉方法分别对阴极结构和 蓝光发光层位置进行了优化,最终获得了高效、色纯度良好、色度随视角变化小的TEWOLED. 最高亮度和效率分别达到9213 cd/m²和3 cd/A,色坐标位于白光区且接近白光等能点, 同时具有良好的视角稳定性,在0°---60°范围内色坐标仅变化(0.02, 0).     

超薄Fe(4?)膜磁特性极化中子反射研究

Ultrathin Fe film 200  V/4  Fe/900  V/MgO（100） has been prepared by molecular beam epitaxy （MBE）. The structure parameters, such as the surface and interface roughness and the thickness of each layer, were obtained by X-ray and neutron reflectivity mea 关键词： 超薄Fe膜 磁特性 极化中子反射 分子束外延     

Lattice site occupation and precipitate dissolution of implanted and irradiated Al(Rh) and Al(Ir)

Abstract

The apparent substitutional fraction, f_s , of Rh and Ir implanted into Al single crystals at 293 K with peak concentrations of 0.17±0.01 at.% is 0.57 ± 0.02 and 0.47±0.02, respectively. Upon annealing to 593 K f_s decreases and the critical angles of the impurities narrow due to partially coherent precipitate formation. Irradiation with 300 keV Ar ions at 77 K with deposited energy densities up to 20 dpa leads to precipitate dissolution accompanied by an increase of f_s up to 0.70±0.02 for Al(Rh) and 0.82±0.02 for Al(Ir). The relatively high f_s values do not decrease during annealing from 77 K to 293 K, indicating that vacancy trapping is not a dominant process. Precipitate formation seems therefore to limit the maximum obtainable f_s values during implantation at 293 K for these systems.     

The characterization of electroplex generated from the interface between 2-(4-trifluoromethyl-2-hydroxyphenyl)benzothiazole] zinc and N,N′-diphenyl-N,N′- bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine

The electroplex between (2-(4-trifluoromethyl-2-hydroxyphenyl)benzothiazole) zinc [Zn(4-TfmBTZ)₂] as an electron-acceptor and N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine (NPB) as an electron-donor was characterized by bilayer, blend, and multilayer quantum-well (MQW) device, respectively. The blend composition and quantum-well number are effective parameters for tuning electroluminescence color. White light with high color purity and color rendering index (CRI) was observed from these devices based on Zn(4-TfmBTZ)₂/NPB. Moreover, the blend and MQW devices all exhibit high operation stability, hence excellent color stability. For the device with 5 mol% NPB in blend layer, its Commission International Del’Eclairage (CIE) coordinate region is x=0.28–0.31, y=0.33–0.35 and CRI is 83.3–91.2 at 5–9 V. For MQW structure device with NPB of 60 nm thickness, its CIE coordinate region is x=0.29–0.32, y=0.31–0.34 and CRI=87.9–92.5 at 10–15 V. Such high color stability and purity and CRI, being close to ideal white light, are of current important for white OLED.     

Zündspannung und normaler Katodenfall der Glimmentladung für Edelgase und reine Molybdänkatoden

Breakdown voltage near PASCHEN -minimum and normal cathode fall of the glow discharge were calculated for inert gases and molybdenum cathodes on the basis of a simple theory. The method used was similar to TAKEISHI 's one. The calculated breakdown voltages are in good agreement with measured values, if back scattering of the y_i -electrons and the distance which electrons travel from the cathode without ionization is taken into account. In the case of the normal cathode fall the values calculated with the same assumptions for inert gases and molybdenum cathodes are much higher (up to 50%) than the well known experimental values. It was concluded, that the y_i-process in the glow discharge ist not the only important one. Comparing the calculated and experimental values of the normal cathode fall we obtain the result, that photons and/or ions from the glow release about 40–60% of all electrons at the cathode.     

Identification of lagrangian coherent structures in the turbulent boundary layer

Using Finite-Time Lyapunov Exponents (FTLE) method, Lagrangian coherent structures (LCSs) in a fully developed flat-plate turbulent boundary layer are successfully identified from a two-dimensional (2D) velocity field obtained by time-resolved 2D PIV measurement. The typical LCSs in the turbulent boundary layer are hairpin-like structures, which are characterized as legs of quasi-streamwise vortices extending deep into the near wall region with an inclination angle θ to the wall, and heads of the transverse vortex tube located in the outer region. Statistical analysis on the characteristic shape of typical LCS reveals that the probability density distribution of θ accords well with t-distribution in the near wall region, but presents a bimodal distribution with two peaks in the outer region, corresponding to the hairpin head and the hairpin neck, respectively. Spatial correlation analysis of FTLE field is implemented to get the ensemble-averaged inclination angle θ _R of typical LCS. θ _R first increases and then decreases along the wall-normal direction, similar to that of the mean value of θ. Moreover, the most probable value of θ saturates at y ⁺=100 with the maximum value of about 24°, suggesting that the most likely position where hairpins transit from the neck to the head is located around y ⁺=100. The ensemble- averaged convection velocity U _c of typical LCS is finally calculated from temporal-spatial correlation analysis of FTLE field. It is found that the wall-normal profile of the convection velocity U _c(y) accords well with the local mean velocity profile U(y) beyond the buffer layer, evidencing that the downstream convection of hairpins determines the transportation properties of the turbulent boundary layer in the log-region and beyond. Supported by the National Natural Science Foundation of China (Grant Nos. 10425207 and 10832001)     

Adsorption of azacrown ethers at solid–liquid interface. Contact angle and neutron reflectivity study

Adsorption of two alkylated N,N′-diaza-18-crown-6 ethers (decyl- and hexadecyl-derivatives, ACE-10 and ACE-16, respectively) on solid surfaces was studied by using contact angle and neutron reflectivity measurements. The solid substrates used were (a) Si covered with a native oxide layer (Si/SiO₂) and (b) Si with sputtered Pt layer (Si/Pt). The sensitivity of neutron reflectivity was drastically improved by applying the intermediate Pt layer of 150 Å, which gave rise to several Kiessig fringes in the experimentally accessible q-range. The position of the fringes is very sensitive to slight changes of the interfacial composition induced by adsorption of a thin monolayer, otherwise very difficult to detect. Unfortunately, in the studied case this sensitivity is immediately lost due to undesired adsorption of a protonated material on the Pt surface exposed to the lab air. A decrease of surface energy (increase of contact angle) of both Si/SiO₂ and Si/Pt upon exposure to toluene solutions of ACEs suggests that the latter are attached to the surface via the hydrophilic azacrown ether head with alkyl chains standing upright towards the liquid phase.     

Time evolution of the microstructures of LaAlO3 thin films grown on Si substrates

The structure and stability of amorphous LaAlO₃ thin films deposited on Si substrates were investigated by an X-ray reflectivity technique. The results show that the film/substrate interface contains a La_xAl_yO_zSi layer and a SiO_x layer. X-ray reflectivity profiles showed a continuous change after the films were exposed to ambient air for six months at room temperature. The X-ray reflectivity simulations suggest a diffusion of La and Al (mostly La) from the LaAlO₃ layer to the La_xAl_yO_zSi layer. This process stopped after about six months, and then the films reached a relative equilibrium state. Moreover, post-air-exposure annealing at 300 °C in air atmosphere could not change the final distributions of La and Al along the normal to the film’s substrate. On the other hand, the leakage-current density slightly decreases after annealing at 300 °C, which might be caused by the decrease of oxygen vacancies in the films. PACS 61.10.Kw; 77.55.+f; 68.60.Dv     

基于等离子体增强化学气相沉积技术的光电子器件多层抗反膜的设计和制作

针对光电子器件端面抗反镀膜的要求,研究了基于等离子体增强化学气相沉积(PECVD)技术的多层抗反膜的设计和制作.首先,对影响SiN_x折射率的因素进行了实验研究,确定了具有大折射率差的SiO₂/SiN_x材料的PECVD沉积条件.根据理论计算分析,设计了四层SiO₂/SiN_x抗反膜结构,能够在70 nm的波长范围内实现低于10^-4的反射率     

同时掺杂磷光和荧光染料的白色有机电致发光器件性能研究

以磷光染料Ir(piq)₂(acac)作为发光掺杂剂,掺入空穴传输性主体材料NPB中得到红色发光层,荧光材料TBP掺入到主体CBP中作为蓝色发光层,制备了结构为ITO/NPB/NPB：Ir(piq)₂(acac)/CBP/CBP：TBPe/BCP/ALq/Mg：Ag的双发光层白色有机电致发光器件.其中ALq₃、未掺杂的NPB和CBP及BCP层分别作为电子传输层、空穴传输层和激子阻挡层.实验中通过调节发光层厚度及Ir(piq)_{2关键词： 磷光 激子阻挡层 有机电致发光}     

Implementation of anti-reflection coating to enhance light out-coupling in organic light-emitting devices

We report significant enhancement of light out-coupling in organic light-emitting devices (OLEDs) by means of anti-reflection coating of magnesium fluoride (MgF₂) on the backside of glass substrate. OLEDs were fabricated by employing the green electrophosphorescent material fac tris-(2-phenylpyridine) iridium [Ir(ppy)₃] doped in 4,4′,8-N,N-8-dicarbazole-biphenyl (CBP) and 0.4 wt% tetrafluorotetracyano-quinodimethane (F4-TCNQ)-doped naphthylphenylbiphenyl diamine (α-NPD) as hole transport layer (HTL). Single-layer MgF₂ with the thickness of λ/4 was then vacuum deposited on the backside of glass substrate of OLED. About two-fold enhancement in luminance with anti-reflection coating of MgF₂ has been observed.     

一种改善红光顶发射OLED色纯度及角度依赖特性的方法研究

在Si/SiO₂衬底上生长金属银作为阳极,4,4,4-tris(3-methylphenylpheny-lamino)-triphenylamine(m-MTDATA):MoOx/m-MTDATA/N,N-bis-(1-naphthyl)-N,N-diphenyl-1,1-biphenyl-4,4-diamine(NPB)作为空穴注入及传输层,发光层采用4,4-N,N-dicarbazole-biphenyl(CBP)掺杂磷光染料(1-(phenyl)isoquinoline)iridium(III) acetylanetonate(Ir(piq)₂(acac))的结构,4,7-di-phenyl-1,10-phenanthroline(BPhen)作为空穴阻挡层及电子传输层,阴极为LiF(1 nm)/Al(2 nm)/Ag(20 nm)复合阴极结构.通过在光取出的复合阴极上方生长一层CBP光学覆盖层,有效地改善了复合阴极膜系的透射率,从而改善了顶发射结构的光学耦合输出特性,在提高器件的正向发光效率的同时还使色坐标往深红光区移动.并且生长光学覆盖层结构的器件角度依赖特性明显得到改善,这对于制作高显示质量的显示器件具有重要意义.在原有结构的基础上增加20 nm的NPB掺杂磷光染料Ir(piq)₂(acac)作发光层,从而得到双发光层结构为NPB:Ir(piq)₂(acac)(1%,20 nm)/CBP:Ir(piq)₂(acac)(1%, 20 nm).由于NPB具有较高的空穴迁移率,避免了由于光学厚度的增加而引起器件工作电压的大幅升高,而双发光层的结构有利于增大激子复合区域,提高辐射复合几率,减少非辐射损耗,实现主客体之间高效的三线态能量传递,相对单发光层顶发射结构,双发光层结构不仅提高了器件的发光效率,而且改善了器件的色坐标.