金属/有机界面势垒对单层有机电致发光器件发光效率的影响

基于高场下电荷的注入过程及激子的解离和复合过程,建立了单层有机发光器件电致发光(EL)效率的理论模型。计算表明：(1)当金属／有机界面势垒高度大于0．3eV时,器件的EL效率很低,降低金属／有机界面势垒可以显著提高器件的EL效率;(2)在较低偏压下,注入过程对器件的电致发光效率起主要作用,但在高偏压下复合过程起支配作用。这一模型可以阐明注入和复合过程对有机发光器件EL效率的影响,对选择发光材料、优化器件结构和提高器件EL效率具有指导意义。     

On the electroluminescence from evaporated thin gold films

Au films with island structure show a spot-like electroluminescence (EL) under a low dc or ac voltage. I–V characteristics and their relation to the EL, and some EL features were investigated.     

Ligand effect on the performance of organic light-emitting diodes based on europium complexes

A series of europium complexes were synthesized and their electroluminescent (EL) characteristics were studied. It was found by comparison that the different substituted groups, such as methyl, chlorine, and nitryl, on ligand 1,10-phenanthroline affect significantly the EL performance of devices based on these complexes. The more methyl-substituted groups on ligand 1,10-phenanthroline led to higher device efficiency. A chlorine-substituted group showed the approximate EL performance as two methyl-substituted groups, whereas a nitryl substituent reduced significantly the EL luminous efficiency. However, β-diketonate ligand TTA and DBM exhibited similar EL performance. The improved EL luminous efficiency by proper substituted groups on the 1,10-phenanthroline was attributed to the reduction of the energy loss caused by light hydrogen atom vibration, as well as concentration quenching caused by intermolecular interaction, and the match of energy level between the ligand and Eu³⁺.     

Fast variations of field-to-density ratio in xenon electroluminescence and electron trapping at the resonance

Summary Xe electroluminescence (EL) has been investigated when varying the applied electric fields in times much lower than the EL relaxation times. The effects of these field jumps can be described within a model which explains the EL in terms of the formation of a peak in the electron energy distribution, near the energy of the subexcitative resonance the Xe exhibits at 7.77 eV. This EL model based on electron trapping at the resonance (ETR) seems to agree well with the reported experimental results. Moreover, starting from the EL rate ratios (measured at the field jumps), one can factorize the rate equation. The two resulting factors have different dependences on the various parameters influencing the EL. Thus, one has a useful instrument for further investigation of the hypothesized underlying phenomena. The authors of this paper have agreed to not receive the proofs for correction. Supported in part by GNEQP-CNR.     

On the influence of the orientation of crystallites on their electroluminescence

The paper considers the influence of the orientation of electroluminescent (EL) barriers on the integrated brightness of EL powders. The results are compared with measurements performed in paper [1].     

Change of the dominant luminescent mechanism with increasing current density in molecularly doped organic light-emitting devices

We have fabricated and measured a series of electroluminescent devices with the structure of ITO/TPD/Eu(TTA)₃phen (x):CBP/BCP/ALQ/LiF/Al, where x is the weight percentage of Eu(TTA)₃phen (from 0% to 6%). At very low current density, carrier trapping is the dominant luminescent mechanism and the 4% doped device shows the highest electroluminescence (EL) efficiency among all these devices. With increasing current density, Förster energy transfer participates in EL process. At the current density of 10.0 and 80.0 mA/cm², 2% and 3% doped devices show the highest EL efficiency, respectively. From analysis of the EL spectra and the EL efficiency-current density characteristics, we found that the EL efficiency is manipulated by Förster energy transfer efficiency at high current density. So we suggest that the dominant luminescent mechanism changes gradually from carrier trapping to Förster energy transfer with increasing current density. Moreover, the conversion of dominant EL mechanism was suspected to be partly responsible for the EL efficiency roll-off because of the lower EL quantum efficiency of Förster energy transfer compared with carrier trapping.     

Spin injection in the multiple quantum-well LED structure with the Fe/AlOx injector

A spin-injection/-detection device has been fabricated based on the multiple quantum well light emitting diode (LED) structure. It is found that only a broad electroluminescence (EL) peak of a full width at half maximum of 8.6 nm appears at the wavelength of 801 nm in EL spectra with a circular luminescence polarization degree of 18%, despite PL spectra always show three well resolved peaks. The kinetic energy gained by injected electrons and holes in their drift along opposite directions broadens the EL pe...     

Density-matrix approach for the electroluminescence of molecules in a scanning tunneling microscope

The electroluminescence (EL) of molecules confined inside a nanocavity in the scanning tunneling microscope possesses many intriguing but unexplained features. We present here a general theoretical approach based on the density-matrix formalism to describe the EL from molecules near a metal surface induced by both electron tunneling and localized surface plasmon excitations simultaneously. It reveals the underlying physical mechanism for the external bias dependent EL. The important role played by the localized surface plasmon on the EL is highlighted. Calculations for porphyrin derivatives have reproduced corresponding experimental spectra and nicely explained the observed unusual large variation of emission spectral profiles. This general theoretical approach can find many applications in the design of molecular electronic and photonic devices.     

Alq_3发光层厚度对有机电致发光器件性能的影响

文章以MoO3为空穴注入层,NPB为空穴传输层,改变发光/电子传输层Alq3的厚度,考察了器件电学和光学性能的变化。结果表明,随着Alq3层增加厚度,器件的电流逐步减小,由此获得Alq3薄膜的电场分布情况;器件发光光谱有少量红移,但长波端明显展宽,短波端强度下降。该文拟合了器件电致发光谱,与实验曲线吻合较好。同时拟合结果也表明,干涉效应主要影响光谱在长波端的强度分布,发光区域分布决定光谱在短波端的强度分布。     

8-羟基喹啉铝电致发光薄膜的电学特性

用真空蒸发沉积方法制备了一种由8-羟基@4铝(发射层)/二胺(空穴输运层)双层有机膜构成的直流薄膜电致发光(EL)器件。获得了发射峰位于520um的绿色EL.EL光谱极相似于8-羟基喹啉铝粉末的光致发光(PL)光谱。发现当首次对该器件结构施加正向偏压激发电致发光时,出现一个形成过程。实验发现与电致发光形成过程相对应的转变电压可能同有机薄膜的品质及电极蒸发条件有关。     

硅衬底垂直结构InGaAlN多量子阱发光二极管电致发光谱的干涉现象研究

测试了硅衬底垂直结构芯片在不同空间角度上的电致发光(EL)谱.指出硅衬底垂直结构InGaAlN多量子阱发光二极管的EL谱中多个峰型来源于干涉现象,而不是来自于多个阱层的发光.干涉峰的疏密反映p型层厚度的一致性,干涉现象的强弱反映p型欧姆接触层反光能力的强弱.芯片法线方向附近发光最强干涉现象最明显,芯片侧边的发光几乎没有干涉现象且发光强度最弱. 关键词： InGaAlN 发光二极管 垂直结构 电致发光     

Recovery of electroluminescence by ageing of ball milled powders

The paper studies the influence of ageing on the electroluminescence of ball milled powders of zinc sulphide and it is shown that partial recovery of the electroluminescence (EL) brightness of ball milled samples occurs. The EL brightness of a non-milled sample did not change with ageing. The recovery of EL ball milled samples is explained by the recovery of the EL barriers by diffusion of the copper ions which were dispersed over the crystallites of the EL powders by ball milling.     

Effect of KI/LiF/CdCl2 on photoluminescent and electroluminescent properties of nanocrystalline (Zn-Cd)S: Cu films

The effect of KI/LiF/CdCl₂ on photoluminescent and electroluminescent (EL) spectra have been reported for (Zn-Cd)S:Cu films. Nanocrystalline films of (Zn-Cd)S:Cu have been prepared using chemical deposition technique in aqueous alkaline bath and their subsequent condensation on substrates. Important results in terms of XRD, SEM, absorption spectra, PL and EL spectra, voltage and frequency dependence of EL brightness are presented. Also, EL brightness waves, EL decay and dependence of EL brightness on nature of electrode material are presented and discussed. SEM studies show best growth conditions in the presence of CdCl₂. Results of XRD studies are associated to ZnS and CdS. Both the studies show average particle sizes to be in the nano order. PL and EL emissions from different films show emission peaks in the blue–green region. Results of absorption spectra show a slight change in band gaps owing to the addition of impurities. Voltage dependence of EL brightness shows effectiveness of acceleration–collision mechanism. Frequency dependence of EL brightness first shows an increase in brightness in the lower frequency range, followed by saturation at higher frequencies. Brightness waves consist of primary and secondary waves, which depend on voltage and frequency of excitation. EL cells with Al electrode give better brightness compared with cells with Ag electrodes. The lifetimes of EL emission are found to be of the order of microseconds.     

Enhanced luminescence related to transparent conductive oxide in ZnS-based EL device fabricated by screen printing method

This experiment is focused to characterize electroluminescence (EL) properties related to transparent conductive oxide (TCO) like In₂O₃ or SnO₂ being dispersedly inserted into the two different layered structures fabricated by screen printing method. X-ray diffraction and FE-SEM measurement were carried out to characterize the material properties of the ZnS-based EL devices depending on the layered structures and the material constitutions. The results show that the enhanced EL intensity with the TCO insertion is approximately 1.2 times greater than TCO-free sample under the 1-layered structure while in no significant improvement of EL intensity is observed under the 2-layered EL structure. But for the EL intensity comparison under the device structure, 2-layered EL structure having a separate dielectric layer is 1.4 times brighter than the 1-layered structure.     

Mechanisms of visible electroluminescence in diode structures on the basis of porous silicon: A review

The main mechanisms of the visible electroluminescence (EL) of porous silicon are reviewed. Characteristics of photoluminescence and EL of diode structures based on porous silicon are compared. Metals having a smaller value of the electron work function (3.6 eV, Mg) than do Al and Au are proposed as the material for making contacts in such diode structures to increase the efficiency of their EL in the visible region of the spectrum. The main problems and prospects of light-emitting devices based on porous silicon are formulated.     

Influence of implantation dose on electroluminescence from Si-implanted silicon nitride thin films

Strong visible electroluminescence (EL) with electrically tunable colors from violet to white has been observed from Si-implanted silicon nitride thin films. Influence of the implanted Si ion dose on both the current conduction and EL properties has been studied. With a larger excess Si concentration, the carrier transport is enhanced leading to a higher EL intensity, but the light emission efficiency is reduced. On the other hand, the increase of the excess Si concentration causes redshifts in the major EL bands and improves the transition of the EL colors with increasing current. The excess Si concentration is also found to have a significant influence on the EL degradation. These findings are important to the application of the Si-implanted thin films in light emitting devices.     

On the improvement of the electroluminescent signal of organic light emitting diodes by the presence of an ultra‐thin metal layer at the interface organic/ITO

The electroluminescent (EL) signal of organic light emitting diodes (OLEDs) based on simple “hole transporting layer/electron transporting layer” (HTL/ETL) structures has been studied as a function of the anode/HTL interface, the anode being an indium tin oxide (ITO) film. It is shown that the electroluminescent (EL) signal increases when a metal ultra‐thin layer is introduced between the anode and the HTL. Experimental results show that the work function value of the metal is only one of the factors which allow improving the EL signal via better hole injection efficiency. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

C-ZnSe:Ga MS发光二极管室温蓝带的发光特性

测量了在77K和290K温度下,Au-ZnSe MIS,Au-ZnSe:Ga MIS,C-ZnSe:Ga MS和C-ZnSe MIS二极管的电致发光光谱,得到了以Au作势垒电极时通常有二个室温蓝带,而以C作势垒电极时只有一个室温低能蓝带。在77K—290K温度范围内,研究了C-ZnSe:Ga MS二极管在正向电压激发下的电致发光光谱随温度的变化。结果表明:室温低能蓝带的起因,在低温下可以归结为同时发射二个纵光学声子的自由激子的发射。文中指出,在C-ZnSe:Ga MS二极管上,观测不到室温高能蓝带,是由于晶体的吸收。由此可见,C-ZnSe:Ga MS结的室温蓝色电致发光的效率比Au-ZnSe MIS结的低得多。     

Electroluminescence of gallium phosphide in the visible spectrum region

The effect of doping impurities and the container material on the color and intensity of electroluminescence (EL) of gallium phosphide crystals grown from the melt in gallium is considered. It is found that the maximum efficiency of red EL is observed in crystals grown in quartz containers, and of green EL — in crystals produced in alundum containers having aluminum nitride coatings. The optimal doping-impurity concentrations are determined for producing diodes with red, yellow, and green radiation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 12–16, April, 1973.     

电致发光成像技术在硅太阳能电池隐性缺陷检测中的应用

论述了一种利用硅太阳能电池在一定偏压下的电致发光(Electroluminescence,EL)成像来检测硅太阳能电池隐性缺陷的方法.硅太阳能电池的EL波长范围为850～1 200 nm.正向偏压下的EL光强反映了少数载流子的浓度及其扩散长度,而反向偏压下的EL区和发光强度对应于电池的缺陷区域和缺陷密度.用硅CCD相机...