光合作用PSⅡ Chl分子传能超快光谱学

利用ICCD皮秒，飞秒扫描成像和飞秒时间分辨光谱装置实验研究了高等植物捕光天线LHCⅡ三聚体和PSⅡ聚粒复合物及PSⅡ核心复合物的超快光谱动力学。经过吸收光谱和发射光谱分析。确定在LHCⅡ三聚体中至少存在7种Chl分子光谱特性，它们是：Chlb653/656^658.7，Chla662.0^665.2,Chla/b670/671^671.6,Chla675.0^677.1,Chla680/681^682.9,Chla685^689.1和Chla695.0^695.6。采用光强10^13光子/cm^2/脉冲激励浓度为30μg/ml的捕光天线LHCⅡ三聚体，在650nm到705nm谱段逐点探测分析处理，产生了两组短寿命组分210fs,520fs和5.2ps,36.7ps及两个长寿命组分1.8ns,2ns。最快的三个寿命210fs,520fs和5.2ps反映了三聚体Chlb分子向Chla分子的激发能传递过程；寿命36.7ps反映了Chla分子向相邻单体Chla分子的激发能传递过程；最长的两个寿命1.8ns和2ns是在三聚体中Chla分子通过中间体Chla分子辐射荧光，分别跃迁回基态的过程，获得的六个寿命组分有把激发能传递时间与Chla/b分子发射光谱相结合的特点，经拟合处理解析PSⅡ颗粒复合物光谱，得到三个组分谱，其峰值分别为686.8nm,692.2nm和694.9nm，与LHCⅡ比较分析，说明天然构型的PSⅡ有很强的吸收光能和有效传递光能的本领，PSⅡ核心复合物的核心天线CP43和CP47，各自含有三种不同状态的Chla分子，CP43有Chla660^661,Chla669^670,Chla682^686,CP47有Chla660^661,Chla669^670,Chla680^681。     

半导体/介质纳米颗粒镶嵌材料的超快激光光谱学

报道了近年来半导体 /介质纳米颗粒镶嵌材料中超快过程的激光光谱学的主要测量方法和技术、探测结果、机理分析和我们的一些见解。     

超快全光开关的实现途径

光开关是光纤通讯系统中的一个重要器件,光开关能根据外加的激励源,有选择性地把光信号从一根光纤传送到另一根光纤.外加激励源可以是力或外加电场、磁场、电磁场等.     

超快非线性干涉仪及其在高速全光信号处理中的应用

本文介绍了一种基于半导体光放大器的单臂干涉仪一超快非线性干涉仪的基本原理,并首次利用Ｊｏｎｅｓ矩阵对超快非线性干涉仪进行了理论工将研究半导体光放大器的理论引入分析超快非线性干涉仪。研究了其在高速全光信号处理中的各种。     

超快光脉冲制造波导和微通道

20世纪 90年代初 ,密歇根大学的研究人员发现飞秒脉冲在与物质相互作用方面与长脉冲有着根本的不同 ,这一发现打开了通向普及激光精密微加工的道路。极短脉宽激光加工基本消除了对周围物质的热流动 ,可避免在多数标准加工技术中常发生的热致基质破坏。材料去除加工由以往用微秒、纳秒脉冲熔融去除变成用飞秒脉冲汽化或升华 ,产生的碎片和表面污染显著减少。另外 ,超短光脉冲与物质作用的阈值现象允许超快激光器以小于光波长的特征尺寸进行材料去除或打孔。在加工介电材料时 ,烧蚀阈值的严格性提高了精度和可再现性。过去两年中 ,许多小组评…     

Ultrafast Hole‐Transfer Dynamics in Polymer/PCBM Bulk Heterojunctions

Ultrafast dynamics of the hole‐transfer process from methanofullerene to a polymer in a polymer/PCBM bulk heterojunction are directly resolved. Injection of holes into MDMO‐PPV is markedly delayed with respect to [60]PCBM excitation. The fastest component of the delayed response is attributed to the PCBM–polymer hole‐transfer process (30 ± 10 fs), while the slower component (～150 fs) is provisionally assigned to energy transfer and/or relaxation inside PCBM nanoclusters. The charge generation through the hole transfer is therefore as fast and efficient as through the electron‐transfer process. Exciton harvesting efficiency after PCBM excitation crucially depends on the concentration of the methanofullerene in the blend, which is related to changes in the blend morphology. Ultrafast charge generation is most efficient when the characteristic scale of phase separation in the blend does not exceed ～20 nm. At larger‐scale phase separation, the exciton harvesting dramatically declines. The obtained results on the time scales of the ultrafast charge generation after PCBM excitation and their dependence on blend composition and morphology are instrumental for the future design of fullerene‐derivative‐based photovoltaic devices.     

Improved Charge Generation via Ultrafast Effective Hole‐Transfer in All‐Polymer Photovoltaic Blends with Large Highest Occupied Molecular Orbital (HOMO) Energy Offset and Proper Crystal Orientation

Improved charge generation via fast and effective hole transfer in all‐polymer solar cells (all‐PSCs) with large highest occupied molecular orbital (HOMO) energy offset (ΔE_H) is revealed utilizing ultrafast transient absorption (TA) spectroscopy. Blending the same nonfullerene acceptor poly{[N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene) (N2200) with three different donor polymers produces all‐polymer blends with different ΔE_H. The selective excitation of N2200 component in blends enables to uncover the hole transfer process from hole polaron‐induced bleaching and absorption signals probed at different wavelength. As the ΔE_H is enhanced from 0.14 to 0.37 eV, the hole transfer rate rises more than one order and the hole transfer efficiency increases from 12.9% to 86.8%, in agreement with the trend of internal quantum efficiency in the infrared region where only N2200 has absorption. Additionally, Grazing‐incidence wide‐angle X‐ray scattering measurements indicate that face‐on crystal orientation in both polymer donor and acceptor also plays an important role in facilitating the charge generation via hole transfer in all‐PSCs. Hence, large ΔE_H and proper crystal orientation should be considered in material design for efficient hole transfer in N2200‐based heterostructures. These results can provide valuable guidance for fabrication of all‐PSCs to further improve power conversion efficiency.     

Ultrafast Spectroscopy of Photoexcitations in Organometal Trihalide Perovskites

Studying the room temperature broadband ultrafast transient response of photoexcitations in three perovskite films, namely MAPbI₃, MAPbI_1.1Br_1.9, and MAPbI_3?xCl_x (MA = CH₃NH₃), allowed unravelling the branching ratio between photogenerated carriers and excitons, a key factor for optoelectronic applications of perovskites. An instantaneously generated mid‐IR photoinduced absorption (PA) band, PA₁ is observed in all three perovskites, as well as a strong derivative‐like band of photoinduced bleaching (PB) and PA (PA₂) close to the corresponding absorption band edge. From the distinguished different decay dynamics of the PA bands in MAPbI₃, PA₁ is interpreted as due to the exciton transition, whereas PA₂ and PB are due to band‐filling effect caused by the photocarriers. In contrast, all bands in MAPbI_1.1Br_1.9 and MAPbI_3?xCl_x share the same dynamics and are therefore due to the same species, namely photogenerated excitons. The transient photoinduced polarization memory (POM) for both excitons and photocarriers as well as the steady‐state photoluminescence (PL) emission are observed in MAPbI₃, but not in MAPbI_1.1Br_1.9 and MAPbI_3?xCl_x because they possess cubic symmetry at room temperature. The estimated long excitons diffusion length (≈150 nm) in MAPbI₃ opens up the possibility of photocarriers generation at interfaces and grain boundaries even when the exciton binding energy is large compare to k_BT.     

Energy Transfer to a Stable Donor Suppresses Degradation in Organic Solar Cells

Despite many advances toward improving the stability of organic photovoltaic devices, environmental degradation under ambient conditions remains a challenging obstacle for future application. Particularly conventional systems employing fullerene derivatives are prone to oxidize under illumination, limiting their applicability. Here, the environmental stability of the small molecule donor DRCN5T together with the fullerene acceptor PC₇₀BM is reported. It is found that this system exhibits exceptional device stability, mainly due to almost constant short‐circuit current. By employing ultrafast femtosecond transient absorption spectroscopy, this remarkable stability is attributed to two separate mechanisms: 1) DRCN5T exhibits high intrinsic resistance toward external factors, showing no signs of deterioration. 2) The highly sensitive PC₇₀BM is stabilized against degradation by the presence of DRCN5T through ultrafast, long‐range energy transfer to the donor, rapidly quenching the fullerene excited states which are otherwise precursors for chemical oxidation. It is proposed that this photoprotective mechanism be utilized to improve the device stability of other systems, including nonfullerene acceptors and ternary blends.     

Ultrafast Electron Transfer in Low‐Band Gap Polymer/PbS Nanocrystalline Blend Films

Ultrafast charge transfer dynamics in hybrid blend films of a low band‐gap polymer poly(2,6‐(N‐(1‐octylnonyl)dithieno[3,2‐b:20,30‐d]pyrrole)‐alt‐4,7‐(2,1,3‐benzothiadiazole)) (PDBT) and PbS quantum dots (QDs) are studied by using ultrafast transient transmission spectroscopy. It is observed that the transient bleaching signal arising from excitons of the PDBT displays a much faster recovery, within the time delay of ≈5 ps, in hybrid films than in the neat PDBT film. In contrast, the bleaching signal resulting from the electron filling of the QDs in hybrid films shows an extra rising component during ≈1–5 ps, which is absent in the pristine QDs. These results indicate the ultrafast electron transfer from the lowest unoccupied molecular orbital energy level of the PDBT to the conduction band of the QDs in the time scale of several ps after laser excitation. A transient absorption signal within 1 ps in the hybrid films is also found, indicating the emergence of charge transfer states (CTs). The CTs formed at the interface of the hybrid blend may facilitate the charge separation and transfer. It is estimated that over 80% of the photoexcited electrons in the PDBT may be transferred into the QDs. The transfer efficiencies show a positive correlation with the power conversion efficiencies of the corresponding hybrid solar cells.     

AsH3分子的振动-平动能量弛豫

用增强型光声池显著降低了光声信号的面损耗，使得AsH3分子的振动-平动能量转移成为造成共振峰展宽的主要因素。光声池内充9．06kPa的AsH3气体，声共振品质因子Q高达374。推导了光声信号振幅与入射光调制频率和样品分子振动-平动弛豫时间的函数关系。理论公式与实验数据的对比表明，对振动热容贡献大的振动能级在气体分子的振动-平动能量转移过程中起主要作用；波动过程中AsH3分子通过最低的两个振动能级进行振动-平动能量交换。     

调制转移光谱的最佳吸收程

调制转移光外差光谱信号的信噪比(SNR)和中心斜率与吸收程等有关.采用吸收程微元叠加法———把吸收程分成n段,计算出每一段产生的调制转移光谱信号元,再对n求和得到总的调制转移光谱信号.利用该方法,理论上研究了调制转移光谱信号相对强度及中心斜率随吸收程的变化,得到最佳吸收程.实验上比较了碘池温度为-15℃时一倍程(40 cm),二倍程(80 cm),三倍程(120 cm)和四倍程(160 cm)的光谱信号信噪比和谱线中心斜率,得到三倍程时信号信噪比和谱线中心斜率为最大,估算得到相应的激光稳频精度为9×10-14(1 s积分时间).通过吸收程优化过程获得的调制转移光谱信号用于激光频率稳定控制,有望获得更高的稳频精度.     

Pump–Push–Probe for Ultrafast All‐Optical Switching: The Case of a Nanographene Molecule

In the last two decades, the three‐beam pump–push–probe (PPP) technique has become a well‐established tool for investigating the multidimensional configurational space of a molecule, as it permits disclosure of precious information about the multiple and often complex deactivation pathways of the excited molecule. From the spectroscopic point of view, such a tool has revealed details about the efficiency of charge pair generation and conformational relaxation in π‐conjugated molecules and macromolecules. In addition, PPP is effectively utilized for modulating the gain signal in conjugated materials by taking advantage of the spectral overlap between stimulated emission and charge absorption in those systems. However, the relatively low stability of conjugated polymers under intense photoexcitation is a crucial limitation for their real employment in plastic optical fibers (POFs) and for signal control applications. Herein, the role of PPP for achieving ultrafast all‐optical switching in π‐conjugated systems is highlighted. Furthermore, new experimental data on optical switching of a newly synthesized nanographene molecule, namely dibenzo[hi,st]ovalene (DBOV), is reported. The superior environmental and photostability of DBOV and, in general, of graphene nanostructures can represent a great advantage for their effective applications in POFs and information and communications technology.