Laser properties of a conjugate polymer (MEH-PPV) in the liquid-excimeric state

We have studied the amplified spontaneous-emission characteristics (ASE) of conjugated poly[2-methoxy-5-(2-ethylhexyloxy)1,4-phenylenevinylene] MEH-PPV in a few organic solutions. The ASE of MEH-PPV appears to arise from its excimeric state. This is perhaps the first report, to the best of our knowledge, on an excimeric-liquid state laser. MEH-PPV in solutions of benzene or tetrahydrofuran (THF) was pumped by the second and third harmonics of an Nd:YAG (532 and 355 nm) for different pump-pulse energies. The ASE of MEH-PPV was compared with the conventional laser dyes Rhodamine B (Rh B) and Rhodamine 6G (Rh 6G). The most important and distinguishing features are: (a) MEH-PPV has a four-times better photochemical stability than Rh B or Rh 6G; (b) the threshold and concentration for the laser action in MEH-PPV is far less than Rh B or Rh 6G.     

External energy transfer in amplified spontaneous emissions from MEH-PPV conjugated polymer

We observed amplified spontaneous emissions (ASEs) in solutions of conjugated polymer under high power neodymium-doped yttrium aluminum garnet (Nd:YAG) laser excitation. A solution of coumarin-485 dye (C₄₈₅) and conjugated polymer (MEH-PPV) was prepared in tetrahydrofuran (THF). Here, C₄₈₅ acted as a donor (with different ratios) while MEH-PPV served as an acceptor (with a constant ratio). Without the donor, MEH-PPV exhibited ASE only in the excimeric state; with the donor, however, it produced ASE in both the monomeric and excimeric states simultaneously. These results clearly show that it is possible to monitor and manipulate the excited state behavior of molecules by using an energy transfer process using laser-excited conjugated polymer.     

Amplified spontaneous emission from internal energy transfer process in the copolymer BEHP-co-MEH-PPV

We have studied the Amplified Spontaneous Emission (ASE) characteristics of the conjugated copolymer poly{[2-[2′,5′-bis(2″-ethylhexyloxy)phenyl]-1,4-phenylenevinylene]-co-[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene]} (BEHP-co-MEH-PPV) in a few organic solutions under optical pumping by the third harmonic of Nd:YAG (355 nm). The results show that in BEHP-co-MEH-PPV, the BEHP-PPV component is capable of forcing MEH-PPV to produce ASE at 560 nm, which appears to arise out of the non-excimeric state of MEH-PPV.The ASE of BEHP-co-MEH-PPV was also compared with the conventional laser dyes Rhodamine B (Rh B), Rhodamine 6G (Rh 6G), and also the new laser material MEH-PPV.     

Low-Threshold Conjugated Polymer Distributed Feedback Lasers on InP Substrate

We demonstrate a low threshold polymer solid state thin-film distributed feedback （DFB） laser on an InP substrate with the DFB structure. The used gain medium is conjugated polymer poly[2-methoxy-5-（2-ethylhexyloxy）-l, 4- phenylenevinylene] （MEH-PPV） doped polystyrene （PS） and formed by drop-coating method. The second order Bragg scattering region on the InP substrate gave rise to strong feedback, thus a lasing emission at 638.9nm with a line width of 1.2nm is realized when pumped by a 532nm frequency-doubled Nd：YAG pulsed laser. The devices show a laser threshold as low as 7n J/pulse.     

Laser from external energy transfer of MEH–PPV conjugated polymer

Mixtures made of poly[2-methyl-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH–PPV) conducting polymer and cresyl violet 670 have been utilized for studying the amplified spontaneous emission characteristics (ASE) in an organic solution under laser excitation. In our earlier communication, we had shown that MEH–PPV alone could produce ASE under pulsed Nd: YAG laser excitation only in its excimeric state. In a follow up study reported here, a mixture of MEH–PPV and cresyl violet in benzene at different ratios were prepared. The results showed that when the mixture was pumped by the third harmonic of Nd: YAG (355 nm), MEH–PPV as a part of the mixture could get excited by pump laser pulse excitation, and transfer its excitation energy externally to cresyl violet to produce ASE. However, MEH–PPV represents here as a donor while CV served as an acceptor.     

富勒烯C60掺杂的共轭高聚物混合薄膜的光谱性质

测量了不同富勒烯C60掺杂浓度的聚对亚苯基亚乙烯衍生物（MEH-PPV）混合薄膜的紫外-可见吸收光谱、稳态荧光和时间分辨荧光光谱。观察到MEH-PPV吸收峰受到明显的抑制以及荧光峰的猝灭。证明混合薄膜内，由于л-л共轭体系的强相互作用在基态发生MEH-PPV向C60的电子转移、形成电荷转移络合物。在光激发下会发生MEH-PPV向C60的激发传递进一步抑制了发光跃迁过程，导致了MEH-PPV荧光的强猝灭效应。     

Polarization characteristics of a light-emitting polymer microring laser

Microring cavities were fabricated by depositing poly(2-methoxy-5-(2’-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV) on glass fibers by a dip-coating method. Laser emissions in whispering gallery modes were observed by pumping with a frequency-doubled Nd:YAG laser. The threshold energy of the MEH-PPV microring laser was as low as 10 nJ per pulse (1.5 μJ/mm²). The polarization characteristics of the microring lasers were studied and a polarization model was developed to explain the observed phenomena. PACS 42.55.Sa; 42.70.Jk     

激光烧蚀制备分布反馈式有机激光器件

采用激光烧蚀的方法结合激光全息技术,直接在高分子聚合物MEH-PPV薄膜表面烧蚀光栅结构,制备了分布反馈式有机激光器。这一方法具有工艺简单、光栅参数的可控性和重复性好等优点。器件MEH-PPV的膜厚是400 nm。利用波长为355 nm的Nd-YAG纳秒激光器进行单脉冲烧蚀,获得的光栅周期和光栅高度分别为370 nm和 100 nm。利用飞秒激光放大器作为泵浦源激射DFB激光器件,得到激射阈值约为182 μJ·cm^-2·pulse^-1,光谱的波峰约在609 nm处,半高宽为4.2 nm。通过改变两光束的夹角获得了周期为360, 370, 380, 390 nm的光栅,它们对应的激光波峰分别为602.91, 609.24, 613.26, 619.01 nm。     

Wavelength dependence of transient photovoltage polarity

Using pulsed laser with different wavelengths, transient photovoltage (TPV) is investigated for the sandwich device of indium tin oxide (ITO)/poly (2-methoxy-5-(2′-ethylhexyloxy)-1, 4-phenylenevinylene) (MEH-PPV) (500 nm)/Al. At laser wavelength of 500 nm, a 0.1 millisecond negative TPV signal appears followed by a positive one lasting 40-80 milliseconds. With increasing laser wavelength, the negative signal becomes weak and disappears when wavelengths λ?560 nm. This work demonstrates the process of exciton dissociation at the interface between ITO and MEH-PPV. A new method measuring the relative dissociation rate at the interface between polymer and electrode is introduced. It is estimated that the dissociation rate at Al interface is 4-8 times of that at the ITO interface.     

Polaron spin-lattice relaxation time in pi-conjugated polymers from optically detected magnetic resonance

We describe a method for obtaining the polaron spin-lattice relaxation time T{SL} in pi-conjugated polymers by measuring the optically detected magnetic resonance (ODMR) dynamics as a function of microwave power and laser intensity. The peculiar ODMR dynamics is well described by a spin dependent recombination model where both recombination and spin relaxation rates determine together the response dynamics. We apply this method to the spin 1/2 ODMR in films of pristine 2-methoxy-5-(2{'}-ethylhexyloxy) phenylene vinylene [MEH-PPV] polymer, as well as MEH-PPV doped with various concentrations of radical impurities. We obtained T{SL} approximately 30 micros in pristine MEH-PPV, but substantially shorter when the magnetic impurities are added.     

ZnO纳米棒在聚［2-甲氧基-5-（2-乙基-己氧基）-1，4-苯撑乙烯撑］固态阴极射线发光器件中的应用研究

利用ZnO纳米棒阵列场发射电极,以SiO₂做为电子加速层制备了固态阴极射线器件,发光层为聚［2-甲氧基-5-（2-乙基-己氧基）-1,4-苯撑乙烯撑］（MEH-PPV）,在交流驱动下得到了MEH-PPV的固态阴极射线发光,探测到了长波峰和短波峰的发射,并和无电子加速层的器件做了比较,证明混合激发模式下的器件在长波长的发光亮度更大. 关键词： 固态阴极射线 ZnO纳米棒阵列 电子加速 电致发光     

MEH-PPV/PEG聚合物电双稳器件的研究

将PEG(聚乙二醇)引入到ITO/MEH-PPV(聚(2-甲氧基,5(2'-乙基己氧基)-1,4-苯撑乙烯撑)/Al三明治器件中,实现了很好的电双稳性能。通过改变PEG的分子量、浓度以及退火温度等条件,对器件性能进行了优化。通过电流-电压(I-V)测试研究了不同器件的性能,结果表明,分子量为4 000的PEG,在30 mg/mL的浓度下,通过120℃退火制备的薄膜,其器件性能最优,电流开关比可以达到10~3以上。利用SEM测试研究了活性层的膜形貌,并结合电流-电压(I-V)曲线的线性拟合,分析了电荷在器件中的传输过程。研究发现,相分离产生的陷阱对电荷的俘获是该器件产生电双稳特性的主要原因。     

掺杂CuPc的MEH-PPV/PCBM有机太阳电池研究

采用旋涂法制备了掺杂铜酞菁(CuPc)的聚(2-甲氧基,5-(2-乙基-乙氧基)-对苯乙炔)(MEH-PPV)/ 富勒烯衍生物(PCBM)有机太阳电池. 测试结果表明:掺杂15% CuPc的MEH-PPV/PCBM太阳电池效率(1.41%)比标准的MEH-PPV/PCBM太阳电池(1.26%)提高12%. 器件的吸收谱和迁移率测试表明CuPc导致的吸收谱增强和迁移率提高是器件效率提高的主要原因. 关键词： 有机太阳电池 CuPc掺杂 MEH-PPV/PCBM器件     

Confirmation on origin of primary electron in solid state cathodoluminescence

This paper utilizes the brightness-voltage waveform curve to investigate the primary electron in solid state cathodoluminescence. The results indicate that the primary electron is from the interface state of SiO₂/MEH-PPV (Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]) under the lower electric field which contributes to the 580-nm emission. With increasing the electric field, the 405-nm emission is obtained, and under this condition, the origin of the primary electron is mainly from tunneling.     

Solvent effects on the electrical and optical properties of composite carbon nanotube/MEH-PPV films

Optical signals were used to modulate the resistance of single-walled carbon nanotube–polymer composite films for development of optical switching devices. Films were fabricated from nanotubes dispersed in poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) solutions in either tetrahydrofuran (THF) or toluene. MEH-PPV was affected by the solvent choice, with THF causing an absorbance shift to shorter wavelengths. Composite films formed from THF dispersions showed 1–4% resistance decreases when illuminated with a green diode laser. Illumination of toluene-based films showed up to 5.4% resistance decreases, smaller than expected based on the polymer solution absorbance. Fluorescent emission from the polymer in toluene appears to inhibit charge transfer from the polymer to the nanotubes. THF films were unaffected by illumination with a red diode laser, while toluene dispersion films showed resistance decreases up to 1%. Nanotube dispersion and film formation reproducibility, evaluated for both the solvents, showed that the solvent affected film resistance and dispersion stability.     

高分子发光二极管载流子注入过程研究

采用交流阻抗谱，电容-电压，电容-频率等实验方法，研究了共轭高分子MEH-PPV(poly［2-methoxy，5-(2-ethylhexoxy)-1，4-phenylene vinylene］)发光二极管的载流子注入过程.对于结构为ITO/PEDOT/MEH-PPV/Ba/Al的发光器件，实验结果表明，电极界面是欧姆接触的，载流子的注入是非平衡的，器件薄膜中存在陷阱容易俘获注入电荷，形成空间电荷区，陷阱密度约为3.75×10¹⁶cm^-3. 关键词： 高分子发光二极管 交流阻抗谱 cole-cole图 载流子注入     

聚合物发光二极管中的负电容效应

采用交流阻抗谱技术,研究了以共轭聚合物(poly［2-methoxy,5-(2′-ethylhexoxy)-1,4-phenylenevinylene］)(MEH-PPV)为发光层,以带有胺基的聚芴共聚物poly［(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)］ (PF-NR₂)为电子传输层的发光二极管的交流响应特性. 对于结构为ITO/P 关键词： 2')" href="#">PF-NR₂ 聚合物发光二极管 交流阻抗谱 负电容效应     

Femtosecond laser micromachining in the conjugated polymer MEH-PPV

Femtosecond-laser micromachining of poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene] films is investigated using 130 fs pulses at 800 nm from a laser oscillator operating at 76 MHz repetition rate. We investigate the effect of pulse energy and translation speed on the depth and morphology of the micromachined regions. We quantified the MEH-PPV photobleaching induced by the fs-laser, and the conditions in which the emission of MEH-PPV is preserved after the micromaching.     

共轭聚合物中掺杂可溶性石墨烯对于OLED和OPV性能的影响

本文重点研究了不同浓度可溶性石墨烯(SPFGO)对于聚[2-甲氧基-5-(2-乙基己氧基)]对苯乙炔(MEH-PPV)/SPFGO复合薄膜的光致发光(PL)、 有机电致发光(OLED)和有机光伏(OPV)性能的影响. 研究发现, 在MEH-PPV中掺杂SPFGO之后, MEH-PPV/SPFGO复合薄膜的光致发光发生了非常强烈的猝灭, 意味着MEH-PPV和SPFGO之间发生了非常强烈的载流子传输. 当SPFGO的浓度较低的时候, 能够提高OLED的性能, 当SPFGO的浓度为0.2%时, OLED的性能达到最佳, 而此时的OPV性能基本没有改变. 当掺杂较高浓度的SPFGO 之后, OPV的性能有了明显的提升, 当浓度为15%时, OPV达到了最佳的性能, 而此时的OLED发生了非常强烈的猝灭. 通过实验数据可以看出, 当SPFGO较低浓度的时候, 起到增强载流子注入的作用, 提升OLED亮度的同时降低了开路电压. 而当SPFGO达到较高浓度时, SPFGO作为电子受体, 可以起到改善MEH-PPV/SPFGO 界面激子分裂和提高OPV性能的作用. 因此, 通过调节SPFGO浓度可以起到独立调控OLED性能和OPV性能的作用. 关键词： SPFGO OLED OPV