基于有机染料盐掺杂薄膜体系的能量转移及光致发光特性研究

利用稳态和时间分辨瞬态光谱研究了有机盐trans-4-［p-(N-ethyl-N-(hydroxyethyl)amino)phenylstyryl］-N-(hydroxyethyl)pyridinium iodide (ASPI)掺杂聚合物PVK(聚乙烯咔唑)薄膜体系的光致发光和能量转移特性. 在ASPI：PVK掺杂薄膜体系中,PVK的荧光强度与寿命随掺杂浓度的升高而降低,表明两者存在有效的Forster能量转移. 通过在相对低浓度的掺杂体系中加入适量高量子效率的Alq3作为能量转移过渡体,形成能量转移级 关键词： 有机染料盐 荧光光谱 荧光寿命 能量转移     

磷光染料掺杂有机分子发光的能量转移研究

用稳态光谱和时间分辨的超快光谱研究了不同浓度磷光染料PtOEP掺杂有机小分子Alq薄膜的发光特性和能量转移.据PtOEP的吸收光谱与Alq的荧光光谱,用Frster理论估算出Alq:PtOEP掺杂体系的能量转移临界半径及其转移效率.稳态荧光光谱显示,在Alq:PtOEP掺杂薄膜中,随着掺杂浓度的升高,PtOEP的发光强度增强,Alq的发光强度逐渐减弱,两者间的能量转移效率与理论计算结果一致.利用时间分辨光谱研究了Alq:PtOEP掺杂薄膜体系的能量转移动力学过程,观察到Alq:PtOEP掺杂薄膜的荧光寿 关键词： 有机掺杂薄膜 稳态光谱 时间分辨光谱 能量转移     

Organic low-dimensional structure electroluminescent material characteristics and devices

Photoluminescence (PL) characteristics of organic doped films are studied as a function of dopant concentration, doped layer thickness. The luminescence properties of doped films are decided by Förster energy transfer rate between host and guest and fluorescence quenching effect of guest. For Alq:rubrene doped film at 5% doping level, we fabricated and characterized organic doped quantum-well structure device, and observed significant quantum size effect. For Alq:QAD doping system, at low doping level of 0.4%, the intermolecular spacing between QAD molecules is relatively large, the interaction between neighboring QAD molecules is very small due to the strong localization of the carriers in the single QAD molecules, the PL properties of Alq:QAD doped films only depends on the PL properties of single isolated QAD molecules, which is somewhat similar to the inorganic quantum dot structure. We also reported the electroluminescent performance of the Alq:QAD system.     

Combinatorial fabrication and screening of organic light-emitting device arrays

The combinatorial fabrication and screening of 2-dimensional (2-d) small molecular UV-violet organic light-emitting device (OLED) arrays, 1-d blue-to-red arrays, 1-d intense white OLED libraries, 1-d arrays to study Förster energy transfer in guest-host OLEDs, and 2-d arrays to study exciplex emission from OLEDs is described. The results demonstrate the power of combinatorial approaches for screening OLED materials and configurations, and for studying their basic properties.     

Effect of energy transfer on electroluminescent performance in blend-layer organic light-emitting devices

The photo- and electroluminescence properties of the blend films of Alq₃ and MEH-PPV with various weight ratios are studied. The Förster energy transfer with a relatively large Förster radius (46.9 Å) and governs the device luminescent performance, although there are some effect of phase separation. It is found that the energy transfer process governs not only the PL properties in the blend films but also the EL performance of the blend-layer OLEDs.     

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.     

Competition Between Energy Transfer and Deactivation During Quenching of Tryptophan Fluorescence of Albumin by Dye Molecules

Using quenching of Trp fluorescence by different dyes, bound to bovine serum albumin, it is shown that the spectral overlap between emission and absorption spectra does not necessarily lead to energy transfer as the sole quenching mechanism. A correlation of the limiting quenching value with the Förster overlap integral was not observed. The energy transfer efficiency was less than the quenching efficiency because of competitive radiationless deactivation processes induced by dye binding.     

Classification of novel thiazole compounds for sensitizing Ru-polypyridine complexes for artificial light harvesting

A systematic study of the Förster resonance energy transfer (FRET) efficiency between thiazole dyes and a ruthenium-polypyridine complex is presented. While ruthenium-polypyridines are conventionally used in artificial light harvesting systems as primary electron donors, their application suffers from rather low extinction coefficients in the visible spectral range and an absorption gap between the ππ^? transitions of the ligands and the MLCT transitions. In this paper it is shown how thiazoles might help to circumvent theses issues. The absorption and emission spectra of the thiazole can be synthetically adjusted to fall into the absorption gap of the Ru dye and to efficiently overlap with the ¹MLCT absorption of the complex, respectively. Thereby, the thiazoles might serve as antenna structures to funnel energy to the Ru-polypyridine unit, which finally can act as a photoactivated primary electron donor. Systematic investigations of the Förster radii of representative thiazole Ru-polypyridine dye pairs corroborate this potential quantitatively.     

聚乙烯基咔唑与Alq3混合薄膜的发光性能与能量传递过程

研究了Alq3与聚乙烯基咔唑(PVK)按不同比例的混合体系制备的薄膜的发光特性.通过对混合薄膜的吸收光谱、激发光谱和发射光谱的分析，研究了PVK与Alq3之间的 能量传递规律.当Alq3与PVK的质量比为1∶7时，能量传递效率最高.用一个由单链模 型扩展到包括杂质的哈密顿量对实验进行模拟，发现该模型能够较好地解释有关的实验结果. 关键词： 吸收光谱 激发光谱 发射光谱 能量传递     

Effect of distance between acceptor and donor on optical properties of composite semiconducting polymer films

The excitation energy transfer from poly(N-vinylcarbazole) (PVK) to tris(8-hydroxyquinoline) aluminum (Alq₃) in composite films was investigated by adding an inert polymer, poly(methyl methacrylate) (PMMA). The energy transfer efficiency calculated from the photoluminescence (PL) excitation spectra is consistent with that from the time-resolved PL decay data of the composite films. We have found a linear relationship between the two kinds of the distances, which are calculated according to volume density and the Förster theory. Experimental results and analyses provide a facile method to infer the energy transfer efficiency and the distance between the donor and the acceptor molecules in the composite films.     

Effects of Metallic Silver Particles on Resonance Energy Transfer Between Fluorophores Bound to DNA

We examined the effects of metallic silver island films on resonance energy transfer (RET) between a donor and acceptor bound to double helical DNA. The donor was 4',6-diamidino-2-phenylindole (DAPI) and the acceptor was propidium iodide (PI). Proximity of the labeled DNA to the silver particles resulted in a dramatic increase in RET as seen from the emission spectra and the donor decay times. Proximity to silver particles results in an increase of the Förster distance from 35 Å an to an apparent value of 166 Å. These results suggest a new type of DNA hybridization assays based on RET over distances much longer than the free-space Forster distance.     

Energy-transferred photoluminescence from thiophene/phenylene oligomer thin films

Photoluminescence (PL) based on Förster energy transfer between p-sexiphenyl (p-6P) and 5,5′-bis(4-phenylyl)-2,2′-bithiophene (BP2T) was investigated for their coevaporated and laminated thin films. In the former films, fluorescence quenching of the p-6P was accompanied by appearance of BP2T fluorescence, which indicated existence of the energy transfer between the donors and the acceptors. The latter films were fabricated by successive depositions of p-6P, MgF₂ and BP2T in which the thickness of the MgF₂ spacer was varied. The energy-transferred acceptor fluorescence was suppressed by the spacer thicker than the Förster distance (∼10 nm).     

掺杂8-羟基喹啉铝薄膜的电致发光特性研究

在具有电致发光(EL)的有机整合染料8-羟基喹啉铝(Alq3)中接以染料罗丹明6G(R6G),用真空热蒸发的方法制备器件,获得了峰值波长575nm的黄色直流薄膜电致发光,从而通过掺杂改变了发光颜色.并在Alq3发光层不同区域插入一掺杂薄层(Alq3:R6G),利用其发光波长与未掺杂部分(Alq3)的不同,以此作为“探测层”,通过对器件光谱及电学特性的测量与分析,探讨了有关发光区域,发光机理,界面对发光影响等基本问题.     

Inter-Layer Energy Transfer through Wetting-Layer States in Bi-layer InGaAs/GaAs Quantum-Dot Structures with Thick Barriers

The inter-layer energy transfer in a bi-layer InGaAs/GaAs quantum dot structure with a thick GaAs barrier is studied using temperature-dependent photoluminescence. The abnormal enhancement of the photoluminescence of the QDs in the layer with a larger amount of coverage considering the resonant Forster energy transfer between the at 110K is observed, which can be explained by wetting layer states at elevated temperatures.     

掺杂8－羟基喹啉铝薄膜的电致发光特性研究

在具有电致发光（ＥＬ）的有机整合染料８－羟基喹啉铝（Ａｌｑ３）中接以染料罗丹明６Ｇ（Ｒ６Ｇ）,用真空热蒸发的方法制备器件,获得了峰值波长５７５ｎｍ的黄色直流薄膜电致发光,从而通过掺杂改变了发光颜色．并在Ａｌｑ３发光层不同区域插入一掺杂薄层（Ａｌｑ３：Ｒ６Ｇ）,利用其发光波长与未掺杂部分（Ａｌｑ３）的不同,以此作为“探测层”,通过对器件光谱及电学特性的测量与分析,探讨了有关发光区域,发光机理,界面对发光影响等基本问题．     

Photoinduced energy transfer in blend films of hole and electron transport materials

The photoluminescence properties of the blend films consisting of the hole transport and electron transport materials, PVK and Alq₃, are studied by steady-state and time-resolved photoluminescence (PL) spectroscopy. Both the relative intensity and the photoluminescence lifetime are intensively dependent of the weight ratios of PVK and Alq₃. The detailed analysis of experiment data provides clear evidence for a Förster energy transfer from excited PVK, as donor, to Alq₃, as acceptor, based on nonradiative resonant transfer mechanism, and allows the determination of Förster radius and the concentration dependent energy transfer efficiency.     

给-受体材料系统中光致发光的峰值波长随浓度变化的理论

高效的给-受体(DA)能量传输材料体系被公认为有机激光器中的重要组成部分。基于Förster传输和受激发射的理论,我们提出了一种在DA系统下发射光谱的数值模型。该模型较好地描述了在DA材料系统中发射光谱随着受主浓度变化的最主要特征,即光致发光谱峰值波长随着受体浓度的增加而非线性增大,并在浓度较高时趋于受体的单体发射波长。     

Abrupt change of luminescence spectrum in single-layer phosphorescent polymer light emitting diode

PVK-based single-layer phosphorescent polymer OLEDs (organic light emitting diodes) with different rubrene concentrations were fabricated and examined for the Förster energy transfer from phosphorescent FIrpic dye to rubrene. We found out that at a certain rubrene concentration the energy transfer occurs abruptly and the transfer shows an abnormal evolution of electroluminescence (EL) spectrum due to the coincidence of peak wavelengths of bis[(4,6-difluorophenyl)-pyridinato-N,C^2′](picolinate) iridium(III) (FIrpic) emission and 5,6,11,12-tetraphenylnaphthacene (rubrene) absorption. With the calculation of Förster radius and average distance between FIrpic molecules, we have related the calculated ratio between the number of FIrpic molecules within to that out of Förster radius with the degree of Förster energy transfer from EL spectra measured in the experiment. Experimental results were found to fit well with the predicted results especially at low rubrene concentrations.     

A Theory of Electronic Energy Transfer in Complex Molecular Systems

The Förster theory for energy transfer is critically reviewed in the context of the present-day theory of nonradiative transitions, and the fundamental tenets of the Förster theory are shown to be erroneous. A new theory of electronic energy transfer is constructed taking into account the electronic transition theory. The intermolecular interaction between donor and acceptor molecules is assumed to perturb electron states of isolated molecules before the donor-molecule excitation. A distinguishing characteristic of the intermolecular interaction is spatial delocalization of the wave functions of electron states of the interacting molecules. It is this fact that has made it possible to realize ordinary photophysical processes between electron states of various molecules in a bimolecular system. In the experiments under study, the result of the intermolecular nonradiative photoprocess is given as evidence of electronic energy transfer from the donor molecule to the acceptor molecule.     

Optical properties of a novel yellow fluorescent dopant for use in organic LEDs

In this paper, the optical properties of a novel organic, 2,8-di(t-butyl)-5,11-di[4(t-butyl) phenyl]-6,12-diphenylnaphthacene (tetra(t-butyl)rubrene) have been investigated. Our results show that there are two peaks in the photoluminescence (PL) spectra of tetra(t-butyl)rubrene (TBRb) which are also confirmed in the electroluminescence (EL) spectra. Photo-quenching of the PL intensity is observed when the irradiation time increases. It is shown that oxidation is the dominant reason for photo-quenching. The absolute refractive index and absorption coefficient have also been determined and the results correlate well with the PL results. The results show that TBRb can be a good dopant to achieve the Förster energy transfer and to assist light emission. The optical properties of TBRb are similar to those of rubrene; however, the PL of TBRb is much stronger than that of rubrene. Finally, although crystalline organics have been commonly reported by heating the sample, we report crystallization of TBRb at low temperature <230 K when the TBRb film is in an amorphous form before cooling. PACS 78.47.+p; 78.55.-m; 81.05.Lg; 85.60.-q