侧链基团对聚合物薄膜瞬态发光性能的影响

采用飞秒激光光谱技术比较研究了两种卟啉侧链聚合物:卟啉丙烯酸酯-苯乙烯共聚物P[(por)A-S]和卟啉铁(Ⅲ)丙烯酸酯-苯乙烯共聚物P[(por)FeA-S]的瞬态发光性能。并采用纳秒激光光谱技术测量了小分子卟啉(TPP)的荧光动力学过程。结果表明:P[(por)FeA-S]具有比P[(por)A-S]快得多的荧光弛豫过程,而P[(por)A-S]的荧光寿命远小于小分子卟啉的荧光寿命。对上述过程进行了分析,P[(por)A-S]的荧光衰变主要来源于聚合物分子链间的相互作用;而P[(por)FeA-S]的荧光衰变除了来源于聚合物分子链间的相互作用外,中央金属离子与配位体之间的电荷转移也对卟啉发色基团的激发态超快无辐射弛豫具有重要的影响,对上述过程的产生机理进行了讨论。     

分子链间距离对于卟啉侧链聚合物稳态及瞬态发光性能的影响

采用荧光光谱技术,测量了一种卟啉侧链聚合物:卟啉丙烯酸酯-苯乙烯共聚物(P[(por)A-S])的稳态和瞬态的发光性能.通过将聚合物P[(por)A-S]掺杂到有机玻璃(PMMA)中,研究了链间距离对于P[(por)A-S]发光性能的影响.结果表明:随着聚合物分子浓度增大,即链间距离减小,导致卟啉侧链基团之间的相互间作用增加,使其激发态无辐射跃迁几率增加,聚合物荧光强度减弱,激发态寿命缩短.讨论了上述过程产生的原因.     

F(o)rster双分子猝灭作用对卟啉侧链聚合物荧光衰变的影响

通过采用时间分辨荧光光谱技术测量了一种卟啉侧链聚合物薄膜:卟啉丙烯酸酯-苯乙烯共聚物poly[porphyrin acrylate-styrene] (P[(por)A-S])在高激发密度下的瞬态荧光特性.实验发现,P[(por)A-S]样品的荧光衰减随聚合物分子浓度的增大而加快.利用Frster机制的双分子猝灭理论对其浓度猝灭的原因进行了分析,理论结果与实验结果符合较好.研究表明,在高激发密度的情况下,Frster机制的双分子作用是加快卟啉侧链聚合物初始荧光衰减和降低其发光效率的主要因素.     

F?rster双分子猝灭作用对卟啉侧链聚合物荧光衰变的影响

通过采用时间分辨荧光光谱技术测量了一种卟啉侧链聚合物薄膜：卟啉丙烯酸酯—苯乙烯共聚物poly［porphyrin acrylate-styrene］ (P［(por)A-S］)在高激发密度下的瞬态荧光特性.实验发现,P［(por)A-S］样品的荧光衰减随聚合物分子浓度的增大而加快.利用Frster机制的双分子猝灭理论对其浓度猝灭的原因进行了分析,理论结果与实验结果符合较好.研究表明,在高激发密度的情况下,Frster机制的双分子作用是加快卟啉侧链聚合物初始荧光衰减和降低其发光效率的主要因素. 关键词： 双分子猝灭 Frster机制 瞬态荧光 卟啉侧链聚合物     

激子旋转弛豫对低掺杂卟啉侧链聚合物荧光衰变过程的影响

利用激子旋转扩散理论研究了一类低掺杂卟啉侧链聚合物中卟啉侧链基团的旋转对其发光动力学过程的影响.研究表明,卟啉侧链基团的旋转行为是导致激发态无辐射能量弛豫的重要途径.基团旋转越容易,能量弛豫速度越快,这可导致一个快速的荧光衰变动力学过程.在卟啉低掺杂浓度和聚合物分子链间距离较大的情况下,卟啉侧链基团的旋转成为影响荧光寿命和发光效率的主要因素.对实验测得的两种样品的荧光弛豫过程进行了拟合,理论结果与实验结果符合较好. 关键词： 激子旋转弛豫 瞬态荧光 卟啉侧链聚合物     

卟啉和钌二元体的超快能量转移

采用超快时间分辨的荧光光谱技术测量了一种由柔性链连接的卟啉-钌二元体分子内的能量转移动力学过程.通过在钌的吸收峰(～453nm)对二元体进行光激发,实验上观测到了从钌基团到卟啉基团的超快能量转移过程(～400ps).而在卟啉的吸收峰(～400nm)对二元体进行光激发,实验上没有观测到从卟啉基团到钌基团的能量转移.采用Frster理论对二元体系能量转移过程的产生机理进行了分析,结果表明,钌和卟啉之间的能量转移来源于基于光谱重叠的偶极-偶极相互作用. 关键词： 卟啉-钌二元体 能量转移 超快激光光谱技术     

利用单分子光学探针测量幂律分布的聚合物动力学

研究聚合物薄膜纳米尺度的动力学特性对于高性能材料的制备具有重要的意义.本文利用尼罗红单分子作为光学探针吸附在聚丙烯酸甲酯(PMA)聚合物链上,研究该聚合物薄膜的动力学特性.通过单分子散焦宽场荧光成像显微镜技术测量了单分子随PMA聚合物链转动弛豫的三维再取向特性,当环境温度高于PMA的玻璃点温度19 K时,发现处于PMA聚合物薄膜中的单分子光学探针的转动态和非转动态的持续时间概率密度服从指数截止的幂律分布.研究结果表明该温度下PMA聚合物薄膜的纳米环境动力学仍存在空间和时间异构性.     

基于电荷转移过程的PAN-C60共聚物薄膜的时间分辨荧光研究

利用吸收光谱和皮秒时间分辨荧光研究PAN－C60星状共聚物的电荷转移过程。PAN－C60共聚物的吸收和荧光光谱结果显示共聚物中存在着电荷转移过程。时间分辨荧光结果表明PAN的荧光衰减遵循双指数衰减规律（一快过程160ps和一慢过程1500ps)，快衰减过程主要来源于聚合物中主链间相互作用产生的空间间接极化子对的影响，慢变过程主要来源于单重态激子的辐射跃迁弛豫。在共聚物中，C60分子的存在除导致PAN激发态寿命缩短外，还影响聚合物链间的相互作用，C60分子对PAN荧光猝 灭作用主要通过慢变过程影响的，而对PAN的空间极化子对的影响主要与其快衰减过程有关。     

高度取向的半导体聚合物薄膜的溶液浸涂法生长及其电荷传输特性研究

有效地控制有机半导体分子取向和堆积特性对实现高性能电子器件具有非常重要的意义,而发展简便高效的溶液相成膜技术是实现这一目的的重要途径.本文采用改进的溶液浸涂法,成功地成长出大面积宏观取向的半导体聚合物P(NDI2OD-T2)和PTHBDTP薄膜.偏光显微镜和极化的紫外-可见光吸收谱测量显示,薄膜中聚合物分子主链骨架沿成膜时液面下移方向择优取向.原子力显微镜观察到聚合物薄膜由纳米尺度的取向有序晶畴构成,畴的取向与分子链的取向一致.采用衬底-溶液界面处表面张力和溶剂蒸发诱导的分子自组织过程来解释浸涂法生长聚合物取向薄膜的微观机理.使用取向的P(NDI2OD-T2)薄膜制备场效应晶体管,显著地提高了电子迁移率(可达4倍),并实现高达19的迁移率各向异性度.这可归因于共轭的聚合物主链骨架择优取向引起电荷传导通路的变化.     

单分子光学探针揭示易混聚合物受限纳米区域的动力学

常规的系综研究方法显示在动力学不对称的易混聚合物中存在着受限区域,但是不能给出受限区域的分布、尺度及受限区域内的动力学分布特征等.单分子光学探针被用来探测苯乙烯高聚物与苯乙烯寡聚物形成的易混聚合物薄膜中的受限纳米区域的动力学.实验发现易混聚合物中存在转动和固定不动的两种动力学形式的单分子,指示着单分子分别耦合到苯乙烯高聚物和苯乙烯寡聚物的聚合物链片段上.转动单分子的分布揭示了易混聚合物薄膜受限区域的分布特征.受限区域的尺度被估计为其可能接近于单分子探针的尺度(约2 nm).受限纳米区域中单分子的转动关联时间的分布揭示了受限纳米区域中聚合物动力学的分布特征.实验发现在含有更高浓度的苯乙烯高聚物的混聚物薄膜中具有更快的动力学行为,从而在单分子水平上揭示了易混聚合物中的受限纳米区域的动力学.     

The effect of intermolecular interactions on photoluminescence of a porphyrin side-chain polymer

Photoluminescence properties and exciton decay dynamics in a porphyrin side-chain polymer, poly[porphyrin acrylate- acrylonitrile (abbreviated p[(por)A-AN]), have been investigated by femtosecond time-resolved photoluminescence spectroscopy. All the luminescences of p[(por)A-AN] films are due to the emissive decay of the photoexcited singlet excitons in the porphyrins. The luminescence efficiencies and lifetimes are increased for samples from pure films to dilute blend films. However, they are increased as the intrachain concentration of the porphyrin sidechain groups is decreased. The intrachain rotation motions of porphyrin sidechain groups result in the initial ultrafast luminescence decays, which are much faster than those due to the interchain interactions. All the samples show no significant red-shift and broadening of the transient luminescence spectra. The interchain and intrachain nonradiative exciton relaxation processes may play an important role in the luminescence dynamics in the p[(por)A-AN] films. The possible origin of different intrachain and interchain dynamic behaviours in p[(por)A-AN] films is discussed.     

Photophysics of polymer-wrapped single-walled carbon nanotubes

Single-walled carbon nanotubes (SWNTs) are successfully dispersed in two conjugated polymer poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) and poly[2-methoxy-5- (2’-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEHPPV) solutions. Steady-state and time-resolved photoluminescence spectroscopy in the near-infrared and visible spectral regions are used to study the interaction of the dispersed carbon nanotube and the wrapped polymer in the nano-hybrids. The SWNTs infrared emission is the signatures of the separation of single semiconducting tubes, the lifetime of the photoluminescence of these tubes is bi-exponential with the first component varying from 6 ps (in MEHPPV wrapped SWNTs) to 14 ps (in PFO wrapped SWNTs), while the second component of the decay for all samples is in the range of 30-40 ps, revealing the intrinsic lifetime of the SWNTs. The study of the photoluminescence of the nano-hybrids in the visible spectral range shows, in the case of the PFO, a relatively strong quenching, the photoluminescence lifetime for the hybrid is more than 100 ps shorter than the one of the pristine polyfluorene solution. For the MEHPPV-SWNT hybrid an opposite behavior is revealed with the photoluminescence lifetime surprisingly longer than the polymer solution. The possible mechanism for the interaction of the two conjugated polymers and the SWNTs is discussed in terms of their electronic band structure.     

MgxZn1-xO薄膜的生长及其光学性能

利用金属有机化学气相沉积(MOCVD)法在蓝宝石(1120)衬底上生长高质量的Mg_xZn_1-xO合金薄膜,实验研究了各种不同Mg组分对样品光学性能的影响。通过光致发光荧光衰减特性对激子发光寿命的研究表明,激子的寿命随Mg组分的增加而增加,当Mg组分达到50%时,激子的寿命为872 ps。     

Optical spin injection and spin lifetime in Ge heterostructures

We demonstrate optical orientation in Ge/SiGe quantum wells and study their spin properties. The ultrafast electron transfer from the center of the Brillouin zone to its edge allows us to achieve high spin polarizations and to resolve the spin dynamics of holes and electrons. The circular polarization degree of the direct gap photoluminescence exceeds the theoretical bulk limit, yielding ～37% and ～85% for transitions with heavy and light holes states, respectively. The spin lifetime of holes at the top of the valence band is estimated to be ～0.5 ps and it is governed by transitions between light and heavy hole states. Electrons at the bottom of the conduction band, on the other hand, have a spin lifetime that exceeds 5?ns below 150?K. Theoretical analysis of the spin relaxation indicates that phonon-induced intervalley scattering dictates the spin lifetime of electrons.     

Decay dynamics of ultraviolet photoluminescence in ZnO nanocrystals

Time resolved photoluminescence (PL) measurements at low temperature are performed on colloidal ZnO nanocrystals dispersed in t-butanol. Considering the particle size dependence of the decay times we conclude that the luminescence is composed of two trap related emissions one of which undergoes lifetime shortening due to a non-radiative process. Initial fast shift of the spectrum within 30 ps is observed and it is interpreted as a fast hole cooling just after the excitation.     

Photoluminescence and positron annihilation spectroscopic investigation on a H(+) irradiated ZnO single crystal

Low temperature photoluminescence and room temperature positron annihilation spectroscopy have been employed to investigate the defects incorporated by 6?MeV H(+) ions in a hydrothermally grown ZnO single crystal. Prior to irradiation, the emission from donor bound excitons is at 3.378?eV (10?K). The irradiation creates an intense and narrow emission at 3.368?eV (10?K). The intensity of this peak is nearly four times that of the dominant near band edge peak of the pristine crystal. The characteristic features of the 3.368?eV emission indicate its origin as a 'hydrogen at oxygen vacancy' type defect. The positron annihilation lifetime measurement reveals a single component lifetime spectrum for both the unirradiated (164?±?1?ps) and irradiated crystal (175?±?1?ps). It reflects the fact that the positron lifetime and intensity of the new irradiation driven defect species are a little higher compared to those in the unirradiated crystal. However, the estimated defect concentration, even considering the high dynamic defect annihilation rate in ZnO, comes out to be ～4?×?10(17)?cm(-3) (using SRIM software). This is a very high defect concentration compared to the defect sensitivity of positron annihilation spectroscopy. A probable reason is the partial filling of the incorporated vacancies (positron traps), which in ZnO are zinc vacancies. The positron lifetime of ～175?ps (in irradiated ZnO) is consistent with recent theoretical calculations for partially hydrogen-filled zinc vacancies in ZnO. Passivation of oxygen vacancies by hydrogen is also reflected in the photoluminescence results. A possible reason for such vacancy filling (at both Zn and O sites) due to irradiation has also been discussed.