Photoluminescence spectral reliance on aggregation order of 1,1-Bis(2'-thienyl)-2,3,4,5-tetraphenylsilole

1,1-Bis(2'-thienyl)-2,3,4,5-tetraphenylsilole (1) was prepared and characterized crystallographically. Silole 1 exhibited aggregation-induced emission (AIE) behavior like other 2,3,4,5-tetraphenylsiloles. Unexpectedly, aggregates formed in water/acetone (6:4 by volume) mixture emitted a blue light that peaked at 474 nm, while aggregates formed in the mixtures with higher water fractions emitted green light that peaked at 500 nm. Transmission electron microscopy demonstrated that the aggregates formed in the mixture with water fraction of 60% were single crystals, while aggregates that formed in the mixture with water fraction of 90% were irregular and poorly ordered particles. The unusual PL spectral reliance on aggregation order was further confirmed by PL emissions of macroscopic crystal powders and amorphous powders of the silole in the dry state. PL spectral blue shifting was observed upon aging of the poorly ordered aggregates formed in mixtures with water fractions of 70-90%, and they finally exhibited the same blue emission as the crystalline aggregates. The as-deposited thin solid film was amorphous and it could be transformed to a transparent crystalline film upon treatment in the vapor of an ethanol/water (1:1 by volume) mixture, along with PL spectral blue shifting due to changing of aggregation order. It was also found that the crystalline film showed a blue-shifted absorption spectrum relative to the amorphous film and the shift of the absorption edge of the spectra could match that of corresponding PL spectra. The FT-IR spectrum of crystal powders of 1 displayed more vibration modes compared with that of amorphous powders, suggesting the existence of different pi-overlaps or different molecular conformations. The crystals of 1-methyl-1,2,3,4,5-pentaphenylsilole and hexaphenylsilole also showed blue-shifted PL emissions of their amorphous solids, with a comparable PL spectral shift of 1. Developing of a silole solution on a TLC plate readily brought about an amorphous thin layer. Our results suggest that crystalline films of AIE-active siloles are potential emissive layers for efficient blue OLEDs with stable color and long lifetime.     

超薄层在白色有机电致发光器件中的应用

以DCJTB为掺杂剂, 以BCP为空穴阻挡层, 研究了两种结构的有机电致发光器件ITO/NPB/BCP/Alq3:DCJTB/Alq3/Al(结构A)和ITO/NPB/BCP/Alq3/Alq3:DCJTB/Alq3/Al(结构B)的电致发光光谱. 实验结果显示, 在结构A器件的电致发光光谱中, 绿光的相对发光强度较弱,增加Alq3层的厚度对绿光的相对发光强度的影响也很小; 而在结构B器件的电致发光光谱中, BCP层与掺杂层(Alq3:DCJTB)之间的Alq3薄层对绿光的相对发光强度影响显著, 用很薄的Alq3层就可以得到强的绿光发射. 进一步改变器件结构, 利用有机超薄层就可以得到稳定的白光器件ITO/NPB(50 nm)/BCP(3 nm)/Alq3(3 nm)/Alq3:DCJTB(1%(w))(5 nm)/Alq3(7 nm)/Al. 随着电压的增加(14-18 V), 该器件的色坐标基本保持在(0.33, 0.37)处不动; 在432 mA·cm-2的电流密度下, 该器件的发光亮度可达11521 cd·m-2.     

Effect of film thickness controlled by ink‐jet printing method on the optical properties of an electroluminescent polymer

Ink‐jet printing (IJP) represents a highly promising liquid processed polymer deposition method for the film preparation of functional polymers in photo‐electronic devices. In this report, the results on the IJP of a fluorene‐based electroluminescent polymer, poly(9,9‐dihexylfluorene‐alt‐2,5‐dioctyloxybenzene) (PF6OC8), from a piezoelectric droplet generator are presented. The polymer film thickness has been found to show an approximate linear relation with the number of droplets per unit area; it is thus convenient to control the film thickness by the space of printed dots in IJP process. In comparison, spin coating approach is also used to prepare polymer films with different thicknesses by varying solution concentration and spinning speed. However, it is found that spin coating is difficult to control the film thickness quantitatively. The influence of film thickness on the photoluminescence (PL) properties of PF6OC8 films prepared by IJP and spin coating is comparatively investigated. For both ink‐jet printed and spin coated films, the intensity of PL spectra first increases and then decreases with increase in the film thickness, probably due to the exciton quenching in thicker films. When the polymer film thickness is at nanoscale, the major peak in the PL spectrum is the 0–0 vibronic emission at about 420 nm, and with increase in the film thickness, the 0–1 vibronic peak at about 440 nm becomes dominant. The red‐shifted PL spectra with increase in film thickness show the change from the 2D exciton state to the 3D one. Copyright © 2009 John Wiley & Sons, Ltd.     

输运层厚度对双层有机器件复合发光的影响

采用ITO/PVK/Alq/Al双层电致发光(EL)结构,制备了三种载流子输运层厚度分别为30、 60、 120 nm,发光层厚度均为300 nm的有机薄膜EL器件,测试其EL谱及J-V特性曲线.根据有机EL器件中载流子的产生和输运过程导出了载流子复合几率及电子和空穴密度分布表示式,用以解释其发光强度随输运层厚度的变化关系,用一维无序结构载流子随机跃迁模型讨论输运层厚度对器件电流密度及启动电压的影响,探讨了载流子在薄膜中的输运过程,其理论与实验符合得很好.     

八-羟基喹啉铝薄膜光致发光的厚度依赖性质

In situ thickness dependent photoluminescence (PL) measurements of tris(8-hydroxyquinoline) aluminum(Alq3) film were performed. At the beginning of Alq3 deposition on the glass substrate, the Alq3 emission showed a sharp red-shift. Further deposition of Alq3 resulted slight red-shift, and finally tended to saturated value. The total red-shift of about 12 nm was observed for the Alq3 film thickness range from 2 to 500 nm.This red-shift was attributed to the change from the 2D to 3D exciton state with increasing Alq3 film thickness. Meanwhile, the PL intensity of Alq3 emission increased continuously, and showed a rate change at the initial deposition of Alq3 due to non-rediative decay of excitons arised from the interaction between excitons and the substrate, and finally tended to saturation with the Alq3 thickness.     

高分子化8-羟基喹啉锂的合成与静电自组装研究

设计合成了甲基丙烯酸二甲氨基乙酯(DM)含量为9.69%的丙烯酸甲酯共聚物(CPA),将制得的5-氯甲基-8-羟基喹啉(CHQ)挂接到CPA上,得到季铵型高分子化8-羟基喹啉(CPA-HQ)后,与金属离子Li+配位得到CPA-HQ-Li.化合物结构通过红外、紫外和荧光光谱等表征.多层超薄膜用CPA-HQ-Li和聚阴离子电解质(全氟磺酸)通过静电自组装制得.自组装膜的紫外和荧光相对于溶液(溶剂为四氢呋喃)发生了红移,膜的紫外吸收强度随组装膜层数增加线性增大,荧光强度随膜层数增加线性递减.高分子化8-羟基喹啉锂溶液和自组装膜的紫外和荧光光谱与文献报道一致.实验结果表明这种材料可用于有机电致发光器件(OLEDs)的制备.     

利用钛保护层在ITO电极上直接制备大面积的超薄氧化铝膜

通过磁控溅射并引入钛保护层, 利用在0.3 mol·L^-1硫酸中20 V电压下二次阳极氧化, 在氧化铟锡(ITO)导电玻璃衬底上直接制备了超薄(约140 nm, 为阳极氧化前Al厚度的一半)、大面积(约4 cm²)的多孔阳极氧化铝(AAO). 扫描电子显微镜结果表明生成的微孔与衬底垂直, 孔径和孔间距分别约为30和60 nm. 我们发现钛保护层的作用是提高了Al层的附着性并且防止ITO被腐蚀, 在此体系中钛不能被其它的金属如铬、金、银或铜代替. 紫外-可见光谱透过率结果显示在阳极氧化过程中Ti被氧化成为透明的TiO₂, 利用10-20 nm的钛保护层以及二次阳极氧化过程, 能够保证高透明度. 在ITO上直接制备的这种透明、有序的AAO纳米结构在光子学、光伏领域和纳米制备等方面具有潜在应用.     

The effect of different gas atmospheres on the structure,morphology and photoluminescence properties of pulsed laser deposited Y3(Al,Ga)5O12:Ce3+ nano thin films

Luminescent properties of Y₃(Al,Ga)₅O₁₂:Ce³⁺ phosphor powder and thin films were obtained. The phosphor powder was used as target material for Pulsed Laser Deposition (PLD) of the thin films in the presence of different background gases. Excitation peaks for the powder were obtained at 439, 349, 225 and 189 nm and emission peaks at 512 and 565 nm. X-ray diffraction indicated that better crystallization took place for films deposited in a 20 mTorr O₂ atmosphere. Atomic force microscope revealed an RMS value of 0.7 nm, 2.5 nm and 4.8 nm for the films deposited in vacuum, O₂ and Ar atmospheres, respectively. The highest PL intensity was observed for films deposited in the O₂ atmosphere. A slight shift in the wavelength of the PL spectra was obtained for the thin films due to a change in the crystal field. The thickness of the films varied from 120 nm to 270 nm with films deposited in vacuum having the thin layer and those in Ar having the thick layer. The stoichiometry of the powder was maintained in the film during the deposition as confirmed by Rutherford backscattering spectroscopy.     

Nucleation and Growth Mechanism of Electropolymerization of Methylene Blue: The Effect of Preparation Potential on Poly(methylene blue) Structure

Nucleation and growth mechanism of electropolymerization of methylene blue (MB) in a basic medium and the effect of preparation potential on poly(MB) film structure were investigated by using cyclic voltammetry, potentiostatic current‐time transient, scanning tunneling microscopy (STM), atomic force microscopy (AFM), and UV‐vis. absorption spectroscopy techniques. Electropolymerization of MB has been achieved by potentiodynamic (cyclic voltammetry) and potentiostatic (constant potential) techniques. The potentiostatic current‐time transients fitted with a theoretical model and morphological studies indicate that nucleation and growth mechanism of poly(MB) starts with a progressive layer‐by‐layer nucleation and growth besides random adsorption. Nucleation and growth of poly(MB) follows a process between progressive layer‐by‐layer and 3‐D instantaneous mechanism resulting in highly‐oriented poly(MB) nanofibers with increasing poly(MB) film thickness. Cyclic voltammetry and morphological studies exhibit that poly(MB) film structure changes depending on the preparation potential. Poly(MB) films prepared at the potential values of 900 and 950 mV show a well‐ordered, smooth surface but at the potential values higher than 1000 mV, rough polymer surface arises as overoxidation takes place. UV‐vis. absorption spectra of poly(MB) film and MB monomer show three peaks. The peak at 410 nm for poly(MB) shows 100 nm blue shift when compared to the MB monomer and is attributed to poly(MB) formation on the electrode.     

非均匀CdSxSe1-x电极的光致发光和电化学发光

用气相扩散法以硒蒸汽处理n-型硫化镉单晶时,在硫化镉晶体表面形成一层组成为CdS_xSe_1-x(0xSe_1-x电极所发射的光谱谱宽(半波频宽,fwhm大于30nm)明显地大于相应的单晶电极所发射光谱的谱宽(半波频宽约为14-25nm).由氩离子溅蚀法所获得的Auger电子能谱数据来看,在实验条件下得到的扩散层的厚度约为0.2-2μm。     

溶剂挥发法制备掺杂激光染料的具有光致发光特性的介孔薄膜

本文采用溶剂挥发法制备了掺杂香豆素151的具有介孔结构的透明二氧化硅薄膜, 并对其荧光发光特性进行了研究.     

Structural and Optical Properties of ZnO Films with Different Thicknesses Grown on Sapphire by MOCVD

IntroductionZnOis one of the most promising materials for pro-ducing ultraviolet laser at room temperature because ofits wide direct band gap(Eg=3.37eV)and large ex-citonic binding energy of60meV.Recently,much at-tention has been paid to short-wavelength …     

Thickness dependence of PL efficiency of organic thin films

Thickness dependence of photoluminescence (PL) efficiency and spectral shape of phosphorescent organic thin films is investigated and theoretically analyzed. The PL efficiency increases with increasing thickness to reach the maximum 92% at around 50 nm. It reduces to 77% at the thickness of 130–140 nm and oscillates between the values upon further increment of thickness. The quenching of excitons at the surface of organic layer significantly reduces the PL efficiency when the film is very thin. If the film is thicker than the critical thickness for the waveguiding of emitted light, the waveguided power is absorbed during the propagation through the organic layer so that apparent PL efficiency is reduced by the amount. Microcavity effect formed by quartz/organic layer/air also affects the PL efficiency. The appropriate thickness to obtain the PL efficiency close to the intrinsic value of a film is just the critical thickness for waveguiding through the film.     

Highly photoluminescent multilayer QD-glass films prepared by LbL self-assembly

A novel and facile preparation method for layer-by-layer (LbL) self-assembled films incorporating quantum dots (QDs) and having intense photoluminescence (PL) from blue to red is presented. Functional sol-gel-derived glass layers prepared by the hydrolysis of 3-aminopropyltrimethoxysilane (APS) or 3-mercaptopropyltrimethoxysilane (MPS) have been used as a linkage between QD layers. Absorption, PL spectroscopy, transmission electron microscopy, and atomic force microscopy were employed for characterization, which revealed that the QDs in the prepared films had a nearly close-packed coverage and were not aggregated. The PL efficiencies of the QDs (CdTe or ZnSe, both are thioglycolic acid-stabilized) dispersed in the films were roughly half that of the initial colloidal solutions but reached 24% before a refractive index correction. The thickness of the red-emitting film with 10 CdTe QD layers was approximately 50 nm. The concentration of QDs in the film derived from the first absorption peak was approximately 0.01 M. Because the PL starts to show a red shift, the obtained concentration is practically the ultimate one in the glass matrix. The mercapto, amino, and carboxyl groups play important roles in LbL self-assembling processes.     

聚(3-己基噻吩)作为光谱增感层在有机太阳电池光谱响应增强中的应用

报道了利用聚(3-己基噻吩)(P3HT)作为前置缓冲层来弥补(4,8-双-(2-乙基己氧基)-苯并[1,2-b:4,5-b']二噻吩)-(4-氟代噻并[3,4-b]噻吩(PBDT-TT-F):[6,6]-苯基-C₆₁-丁酸甲酯(PC₆₁BM)共混体相异质结(BHJ)电池对450-600 nm处光谱响应不足的新的器件结构设计思路. 光谱带隙为1.8 eV的PBDT-TT-F 在550-700 nm处有很强的光谱吸收, 在有机太阳电池器件上有很好的应用潜能. 但其在350-550 nm处的吸收不强, 影响了器件对太阳光谱的利用效率. 与此相比, P3HT薄膜的光谱吸收主要在450-600 nm范围内, 同PBDT-TT-F 形成良好的互补关系. 新设计的器件外量子效率(EQE)研究结果表明, 利用P3HT 作为前置缓冲层可以与PBDT-TT-F:PC₆₁BM薄膜中的PC₆₁BM形成平面异质结, 从而拓展了器件在450-600 nm处的光谱响应范围,实现光谱增感作用. 优化P3HT的厚度为20 nm左右, 器件对外输出的短路光电流密度从11.42 mA·cm^-2提高到12.15 mA·cm^-2, 达到了6.3%的提升.     

蓝色磷光材料FIrpic的发光特性

研究了掺杂浓度及热退火对磷光材料双(4,6-二氟苯基吡啶-N,C2?)吡啶甲酰合铱(FIrpic)发光性能的影响.不同掺杂浓度的薄膜及有机电致发光器件(OELDs)的发光颜色都随FIrpic浓度的增大由蓝色逐渐变化到黄绿色.纯FIrpic薄膜的吸收光谱和光致发光(PL)光谱在440-480nm范围内有明显的光谱重叠,476nm处的发光强度随FIrpic掺杂浓度增大而降低主要是由自吸收效应引起的.测量了不同激发密度下的光致发光光谱和不同掺杂浓度下的电致发光(EL)光谱,发现530nm处的发光强度随激发强度或掺杂浓度的增大而增强,证实了530nm处的发光是来源于FIrpic分子间的激基缔合物发光.通过比较热退火前后薄膜微观形貌及电致发光器件光谱的变化,进一步证实了热退火促进FIrpic分子聚集,增强了FIrpic分子间的辐射跃迁发光.通过调控FIrpic掺杂浓度和优化器件结构,并对器件进行热退火处理得到一系列发光颜色从蓝色逐渐变化到黄绿色的有机电致发光器件.     

Effect of Al-doping on the structure and optical properties of electrospun zinc oxide nanofiber films

Electrospun ZnO precursor nanofibers of average diameters 122±64 nm, 117±44 nm and 110±39 nm were fabricated by controlling the Al concentration of a polymeric solution. The resulting nanofibers were characterized by the XRD, SEM, EDS, TEM, XPS and PL. The electrospun Al-doped ZnO nanofiber films were polycrystalline and composed of densely packed grains, with crystallite size ranging from 28.7 nm, 25.7 nm, 25.4 nm to 20.4 nm corresponding to the atomic concentration of aluminum from 0, 1.6, 2.5 to 5.8 at.%. The incorporation of aluminum resulted in a decrease trend in the grain size and lattice parameter of the ZnO nanofiber films. The room temperature PL spectra of all samples show three different emissions, including UV (ultraviolet) emission with an obvious blue shift, Vis (visible) emission and NIR (near infrared) emission, the intensity of which decreases monotonically as the doping concentration is increased except for the highest doping level. The impurity content correlates with changes in the PL spectra, and the appropriate Al doping can improve the optical properties of ZnO nanofibers. The small size effect and Al-doping or the impurity incorporation should be responsible for the blue shift observation in Al-doped ZnO nanofiber films.     

Enhanced Fluorescence Using an Optical Interference Mirror Overlaid with Silver Island Film

Fluorophores overlaid on an optical interference mirror composed of a metal and thin dielectric layer demonstrate enhanced fluorescence. Fluorescence is also enhanced by silver nanostructures such as silver island films, which excite localized surface plasmon resonance. An optical interference mirror surface was overlaid with a silver island film to amplify the fluorescence enhancement. The optimal thickness of the silver island film (100 nm) was evaluated from transmittance and surface roughness measurements. At this thickness, the fluorescence was amplified sixteen-fold. The thickness of the interference layer was optimized at 40 nm providing a one hundred-sixty fold fluorescence enhancement of rhodamine B. However, only a four-fold improvement in sensitivity was achieved for the determination of a labeled streptavidin using biotin immobilized on the silver island film interference mirror.     

Versatile route for tuning optical properties of poly(2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene)

In this contribution, we report a versatile method for tuning optical properties of poly(2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene) (MEH‐PPV) in its solution with 1,2‐dichloroethane, accomplished by reacting with pyridinium formate (PF), a volatile organic salt. We can systematically control the positions of absorption and photoluminescent (PL) spectra of MEH‐PPV by adjusting the concentration of PF in the solution. The addition of 10 vol % PF caused a blue‐shift in the absorption spectra by about 65 nm. When the concentration of PF decreased to 0.1 vol %, the blue‐shift occurred to a lesser extent, about 25 nm. The measurements of PL spectra showed similar behaviors. The λ_max shifted from 558 nm to 546 and 552 nm when 10 and 0.1 vol % of PF were added, respectively. The changes of PL colors from orange to yellow and green, respectively, were observed by naked eyes. Structural investigation by nuclear magnetic resonance and Fourier‐transformed infrared spectroscopy indicated that the changes of the optical properties were due to chemical modifications along the main chain and the side groups of MEH‐PPV. These results implied a simple route for engineering the HOMO–LUMO energy gap of MEH‐PPV, which could be utilized in advanced applications such as organic light‐emitting devices and solar cells. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 696–705, 2009     

In-situ synchrotron radiation SAXS study of structural deformation memory effect of the interfacial region in Al2O3/LDPE composite film

This paper employs the SAXS technique to study the microstructure evolution of nano Al₂O₃/low-density polyethylene (LDPE) composite film during temperature increase and decrease (including interfacial layer thickness, mass fractal and surface fractal), and discusses the deformation memory effect (DME) mechanism. Compared with the case of pure LDPE, there are some new phenomena observed in the Al₂O₃/LDPE composite film, such as an interfacial layer and surface fractal. The experimental results showed that, when the temperature rose from 25 °C to 180 °C, the interfacial layer thickness of the composite film increased from 2.8 nm to 3.5 nm, and the surface fractal dimension increased from 1.2 to 2.0, with the lamellar crystal of the PE molecular chains melting. When the temperature dropped from 180 °C to 30 °C, the interfacial layer thickness decreased from 3.5 nm to 3.0 nm, and the surface fractal dimension changed from 2.0 to 1.2, with the PE molecular chains recrystallizing. We found that the DME of the interface layer is that thickness and area increase when temperature rises and decrease when temperature decreases. The addition of Al₂O₃ nanoparticles into the polymer results in the adsorption of space charges in the matrix onto the nanoparticles and in the interfacial regions, which efficiently inhibits the space charge accumulation of the composite material in the gradient electrical field.