Development of organic light‐emitting diodes for electro‐optical integrated devices

Organic light‐emitting diodes (OLEDs) are discussed for electro‐optical integrated devices that are used for optical signal transmission. Organic optical devices including polymeric optical fibers are used for optical communication applications to realize polymeric electro‐optical integrated devices. The OLEDs were fabricated by vacuum process, i.e. the organic molecular beam deposition (OMBD) technique or a solution process on a polymeric or a glass substrate, for comparison. Optical signals faster than 100 MHz have been created by applying pulsed voltage directly to the OLED utilizing rubrene doped in 8‐hydoxyquinolinum aluminum (Alq₃), as an emissive layer. OLEDs fabricated by solution process utilizing rubrene doped in carrier‐transporting materials have also discussed. OLEDs utilizing polymeric materials by solution process are also fabricated and discussed. Moving‐picture signals are transmitted utilizing both vacuum‐ and solution‐processed OLEDs, respectively.     

氧化石墨烯的多色发光及其在荧光成像中的应用

氧化石墨烯作为石墨烯的一种带隙打开的衍生物,极大地丰富了其光学性质,并拓展了它在传感和成像方面的应用,特别是氧化石墨烯限域的π共轭结构对构建发光碳材料提供了十分便利的条件。目前,有大量的研究工作报道了氧化石墨烯及其衍生物能够产生多种颜色的荧光信号,然而,系统地总结这些研究去揭示氧化石墨烯发光机理的相关工作还比较少。本文总结了关于发光氧化石墨烯纳米材料的合成及其在光学成像方面应用的大量研究工作,为进一步开发新型的发光氧化石墨烯材料提供一些建设性意见。     

有机电致发光白光器件的研究进展

在十多年的时间里,有机电致发光二极管(Organic Lightemitting Diodes,OLEDs)的研究和应用取得了长足的进展。有机电致发光器件具有许多优点,例如:自发光、视角宽、响应快、发光效率高、温度适应性好、生产工艺简单、驱动电压低、能耗低、成本低等,因此有机电致发光器件极有可能成为下一代的平板显示终端。有机电致发光白光器件因为可以用于全彩色显示和照明,已成为OLED研究中的热点。介绍了有机电致发光白光器件的研究进展,按发光的性质将白光器件分为荧光器件和磷光器件两类,按发光层数将白光器件分为单层和多层器件,对相关材料、器件结构、发光机理等方面进行了讨论。     

Unlocking The Inherent Luminescence of Eu2+/Eu3+ by Light-Induced Oxidation for Invisible Optical Storage

Color-tunable luminescent materials are increasingly recognized for their potential applications in high-security anticounterfeiting and optical storage technologies. However, luminescent materials with high-contrast photoswitching behavior that change their luminescence properties in response to external stimuli are extremely scarce. In this study, a time-dependent color-tunable luminescent material, Na₂BaSiO₄:Eu²⁺ (NBSO:Eu), is introduced. This material leverages the inherent luminescence of Eu²⁺/Eu³⁺ through a light stimulus. Under 365 nm irradiation, the blue luminescence of Eu²⁺ gradually degraded over time, reaching a luminescence contrast of up to 88%. This degradation is accompanied by a color change of the emitted light from blue to red (Eu³⁺). These color changes can be reversibly tuned by alternating light or thermal stimuli. Experimental investigations revealed that the photogenerated Eu³⁺ ions and defects, acting as killer centers, induced multicolor luminescent switching behavior. Owing to their unique optical properties, NBSO:Eu offers exciting opportunities for designing advanced dynamic anticounterfeiting and invisible optical storage.     

双功能电极改善有机发光器件效率滚降的研究

针对磷光器件存在严重的效率滚降,进而制约有机电致发光器件的实用化进程的问题,提出采用超声喷涂Poly(3,4-ethylenedioxythiophene)Polystyrene Sulfonate(PEDOT:PSS)作为透明电极,制备了红、绿、蓝三色有机电致发光器件.利用超声喷涂工艺材料利用率高的特点,起绝缘作用的水溶性PSS分子链在PEDOT:PSS透明电极中得到保留,使该透明电极具有空穴缓冲作用.这种双功能性,提高了器件在高电流密度下的载流子平衡性,降低了红、绿、蓝三色发光层中的极化子浓度,改善了红、绿、蓝三色器件的效率滚降问题,从最高外量子效率所在亮度到10000cd/m^2的电流效率滚降分别仅为14.9%、12.4%和16.0%.该结果表明,双功能性电极的引入显著改善了有机电致发光器件中载流子平衡性,具有降低三基色器件效率滚降的普适性,对实现高亮度、高效率发光器件具有重要意义.     

含稀土铕(Ⅲ)配合物光学树脂的制备及光学性能的研究

报道了将多种稀土铕（Ⅲ）的二元及三元配合物复合于苯乙烯（St)／甲基丙烯酸（HMA）的共聚体系,制备得到具有发光功能的透明光学树脂,对其光学性能进行研究。同时,考察了稀土配合物的含量对聚合物 透明性、发光性能的影响。     

GaN基薄膜半导体材料不同非线性效应的竞争关系

采用金属有机化合物化学气相沉积方法生长了未掺杂GaN,p型Mg掺杂GaN,InGaN/GaN多量子阱等薄膜半导体材料,研究了其在800 nm飞秒激光激发下的非线性光学性质.实验结果表明,在800 nm飞秒激光激发下,多光子荧光、二次谐波等非线性光学信号之间存在着竞争关系,反映出不同非线性光学信号对激发光的能量分配存在着竞争,并通过其非线性光学信号强度与激发强度之间的依赖关系进行了验证.同时,本文对其竞争机理进行了初步探究.     

Characterization of amorphous organic thin films, determination of precise model for spectroscopic ellipsometry measurements

The optical properties of tris(8-hydroxyquinoline) aluminum (Alq₃), N,N′-diphenyl-N,N′-bis(1-naphthyl)-1-1′biphenyl-4,4″diamine (α-NPD) and other amorphous organic materials for OLEDs application, e.g. 4,4-bis(2,2-diphenyl vinyl)-1,1-biphenyl (DPVBI) and Spiro-DPVBI have been studied by multi-angle spectroscopic ellipsometry (SE). The thin films of these materials have been deposited by organic vapor phase deposition (OVPD). The structural characterization has been performed using atomic force microscopy (AFM) and X-ray reflectometry (XRR). Comparison of the measurements using these different independent techniques enables the precise determination of the optical model for dielectric function of these thin films. The detail analyses on Alq₃ and α-NPD show that the Kim model with Gaussian broadening provides a significantly better fit to the ellipsometry data than the frequently used harmonic oscillator model. This conclusion is further proved by performing similar measurements on other amorphous organic samples for OLEDs application, e.g. DPVBI and Spiro-DPVBI. This result can be explained by the characteristic features of electronic states in organic molecules.     

Theoretical study of optical and electronic properties of the bis‐dipolar diphenylamino‐endcapped oligoarylfluorenes as promising light emitting materials

We present a detailed study of the structural, electronic, and optical properties of the bis‐dipolar emissive oligoarylfluorenes, OF(2)Ar‐NPhs. The aim of our quantum‐chemical calculations is to investigate the role of the transition and the influence of the optical properties of the various central aryl cores in the oligoarylfluorenes. Geometry optimizations were performed for the ground‐state and for the first electronically excited‐state. The absorption and emission spectra were calculated using time‐dependent density functional theory (TD‐DFT). The results show that the HOMO, LUMO, energy gap, ionization potentials (IP), electron affinities (EA) and reorganization energy (λ) of the oligoarylfluorenes are significantly affected by the electronic withdrawing property and the conjugated length of the central aryl core. Consistently, the stronger the electron withdrawing strength, the lower the LUMO energy is. This thus improves the electron‐accepting and transporting properties by the low LUMO energy levels. The absorption and emission spectra of this series of bis‐dipolar molecules exhibit red shifts to some extent by the electronic nature of the electron affinitive central core in the oligoarylfluorenes. All the calculated results show that the oligoarylfluorenes are promising as useful light emitting materials for OLEDs. Copyright © 2007 John Wiley & Sons, Ltd.     

Scintillation mechanisms and limiting factors on each step of relaxation of electronic excitations

Scintillation mechanisms in insulating materials are described in the general case of a simple electronic band structure and in special cases of most interest for applications: rare-earth-containing crystals and cross-luminescent materials with a more complicated electronic band structure. At each of the three main steps of the energy relaxation, namely, (i) the creation of electronic excitations, (ii) the transfer to luminescent centers, and (iii) the emission of luminescent centers, factors limiting the performance of the scintillators are identified and the related processes described.     

Near infrared organic light-emitting diodes based on acceptor-donor-acceptor (ADA) using novel conjugated isatin Schiff bases

Fabrications of a single layer organic light emitting diodes (OLEDs) based on two conjugated acceptor-donor-acceptor (ADA) isatin Schiff bases are described. The electroluminescent spectra of these materials range from 630 to 700 nm and their band gaps were measured between 1.97 and 1.77 eV. The measured maximum external quantum efficiencies (EQE) for fabricated OLEDs are 0.0515% and 0.054% for two acceptor-donor-acceptor chromophores. The Commission International De L’Eclairage (CIE) (1931) coordinates of these two compounds were attained and found to be (0.4077, 0.4128) and (0.4411, 0.4126) for two used acceptor-donor-acceptor chromophores. The measured I-V curves demonstrated the apparent diode behavior of two ADA chromophores. The turn-on voltages in these OLEDs are directly dependent on the thickness. These results have demonstrated that ADA isatin Schiff bases could be considered as promising electroluminescence-emitting materials for fabrication of OLEDs.     

Theoretical studies on the electronic and optical properties of arene‐ versus fluoroarene‐thiophene co‐oligomer

A series of regiochemically varied and core size extension‐modulated arene‐ and fluoroarene‐thiophene co‐oligomers and the unsubstituted sexithiophene α6T were investigated theoretically to explore their electronic and optical properties. These phenylene‐thiophene oligomers show great potential for application in organic light‐emitting diodes (OLEDs), organic diode lasers, and organic thin‐film transistors (OTFTs) because of their feasible tuning of optical and electronic properties by the various structural tunings. Density functional theory (DFT) and the ab initio HF were employed to investigate the geometric and electronic structures of the oligomers in the ground state, and the singles configuration interaction (CIS) methods were used to study the lowest singlet excited state. The lowest excitation energies (E_gs), the radiative lifetime τ, and the maximal absorption/emission wavelength of the oligomers were studied within time‐dependent DFT (TDDFT). All calculations were performed using the 6‐31G(d) basis set. The results show that the HOMOs, LUMOs, energy gaps, ionization potentials (IPs), electron affinities (EAs), and reorganization energies are significantly affected by the various structural tunings in these co‐oligomers, which is important for the improvement of the hole and electron injection into OLEDs. Interestingly, the LUMO energy of 1b , 2b , and 3b is lower than that of α6T and 1a , 2a , 3a by about 0.12 ～ 0.47 eV, indicating that the fluorophenyl‐substitution has significantly improved the electron injection properties of the oligomers. Copyright © 2008 John Wiley & Sons, Ltd.     

NIR-and upconverted luminescence from rare-earth sodalites

In the recent past, numerous attempts have been made to utilize nano-, meso-, and microporous materials as hosts for luminescent guest species. The accessible spectral range now spreads from the vacuum ultraviolet to the near infrared (NIR), if sodalites are included in this scope. Although borderline materials in this context with respect to pore sizes, examples of the versatility of sodalites in accommodating small but efficient luminescent entities are discussed. In particular, optical materials whose spectral range of operation is allocated in the NIR have recently attracted our attention and will form the focus of this report.     

Design of perylene-diimides-based small-molecules semiconductors for organic solar cells

A series of perylene-diimide-based small molecules have been designed to explore their optical, electronic and charge transport properties as organic solar cell materials. The frontier molecular orbitals analysis has turned out that the vertical electronic transitions of absorption are characterised as intramolecular charge transfer between perylene diimide moieties and substituent aromatic groups. Our results suggest that the optical and electronic properties and reorganisation energies are affected by the introduction of different aromatic groups to these molecules. The calculation results showed that the designed molecules own the large longest wavelength of absorption spectrum, the oscillator strength and absorption region values. On the basis of the investigated results, the designed molecules could be used as solar cell material with intense broad absorption spectra. Furthermore, they are expected to be the promising candidates for hole and/or electron transport materials.     

Luminescence mechanisms of green and blue organic light-emitting devices utilizing hole-blocking layers

Optical and electrical measurements on green and blue organic light-emitting devices (OLEDs) with and without hole-blocking layers (HBLs) were performed, and the luminescence mechanisms of green and blue OLEDs utilizing HBLs were investigated by using energy band diagrams and carrier density distributions. The dependence of the electroluminescence efficiencies on the existence of HBLs was described on the basis of a luminescence mechanism. The density distributions of the electrons and the holes in OLEDs under applied electric fields were estimated from the energy band diagrams, taking into account the electronic parameters and the layer thicknesses. The luminescence efficiencies and the color chromaticities were significantly affected by the existence of the HBLs. These analyses can help improve understanding of the luminescence mechanisms at play in and the electroluminescence efficiencies of green and blue OLEDs with HBLs, and the present results provide important information on the optical properties for enhancing the efficiencies of OLEDs operating in the green and the blue regions of the spectra.     

有机电致发光器件及其稳定性问题

有机发光二极管（ＯＬＥＤｓ）即将实用化,但其稳定性仍是急需解决的关键问题。文章简要综述了ＯＬＥＤｓ及其稳定性问题,着重从ＯＬＥＤｓ的失效过程、水汽和氧气、电极材料及其界面对ＯＬＥＤｓ稳定性的影响、有机材料本身的稳定性等方面讨论了ＯＬＥＤｓ的稳定性。     

有机发光材料中的三重激发态

有机发光材料有望广泛应用于新一代柔性光电子器件。由于自旋多重性,有机分子发光材料 中单重激发态和三重激发态转换较慢,限制有机发光器件特别是电注入荧光器件的效率。我们介绍 下近年来通过分子设计操控激发不同时间尺度三重态的动力学来突破这一限制的策略,通过控制激 发单重态和激发三线态之间的电子耦合,利用热激子系间窜越、反向系间窜越、激发三重态稳定化 等过程能够有效提高有机发光材料的发光效率。在此基础上实现的热活化延迟荧光、有机长余辉发 光等在有机发光二极管、传感器、生物成像等领域有重要潜在应用价值。     

Photo-Fries-based photosensitive polymeric interlayers for patterned organic devices

This work reports on the investigation of the photosensitive polymer poly(diphenyl bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate) (PPNB), which undergoes the photo-Fries rearrangement upon illumination with UV-light, used as interfacial layers in organic electronic devices. Two cases were investigated: the use of a blend of PPNB with poly-vinylcarbazole (PVK) as an interlayer in para-sexiphenyl (PSP) based organic light emitting diodes (OLEDs) and the use of PPNB as gate dielectric layer in organic field effect transistors (OFETs). The photo-Fries rearrangement reaction causes a change of the polymer chemical structure resulting in a change of its physical and chemical properties. The electroluminescence spectra and emission of the PSP OLEDs are not affected when fabricated with a non-UV-illuminated PPNB:PVK blend. However, the electroluminescence is totally quenched in those OLEDs fabricated with UV-illuminated PPNB:PVK blend. Although the dielectric constant of PPNB increases upon UV-treatment, it is demonstrated that those OFETs built with UV-treated PPNB as gate dielectric have lower performance than those OFETs built with non-UV-treated PPNB. Furthermore, the effect of the UV-illumination of PPNB and PPNB:PVK blend on the growth of the small molecules C₆₀ and PSP has been studied by atomic force microscopy. Using photolithography, this kind of photochemistry can be performed to spatially control and tune the optical and electrical performance of organic electronic devices.     

Synthesis and luminescent properties of PEO/lanthanide oxide nanoparticle hybrid films

In this study, we investigate the optical properties of lanthanide oxide nanoparticles dispersed in poly(ethylene oxide) (PEO) network as thermally stable polymeric films. The aim of this work is both to keep a good optical transparency in the visible domain and to obtain luminescent materials after incorporation of nanoparticles. For this purpose, we develop luminescent nanocrystals of oxides containing terbium ion as a doping element in Gd₂O₃. These sub-5-nm lanthanide oxides nanoparticles have been prepared by direct oxide precipitation in high-boiling polyalcohol solutions and characterized by luminescence spectroscopy. PEO/lanthanide oxide nanohybrid films are prepared by radical polymerization of poly(ethylene glycol) methacrylate after introduction of lanthanide oxide particles.As a first result; the obtained films present interesting luminescence properties with a very low lanthanide oxide content (up to 0.29 wt%). Furthermore, these films are still transparent and keep their original mechanical properties.Prior to describe the specific applications to optical use, we report here the dynamic mechanical analysis (DMA), X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), and luminescent properties of. nanohybrid films.