5(6)羧基荧光素敏化TiO2纳米粒子的光致电子转移的荧光特性研究

通过水解TiCl₄制备了锐钛矿结构TiO₂纳米粒子, 并用时间分辨荧光光谱研究了5(6)CFL(5(6)-Carboxyfluorescein, 简称5(6)CFL)染料敏化TiO₂纳米粒子体系的光致电子转移动力学. 5(6)CFL染料敏化TiO₂纳米粒子能形成电荷转移复合物, 这归因于染料分子的激发电子态波函数Ψ(D^*)与电荷分离态波函数Ψ(D⁺ +e^-)之间的耦合作用. 当激发5(6)CFL染料敏化TiO₂纳米粒子体系时, 电子以两种不同方式注入TiO₂纳米粒子导带: 第一, 通过5(6)CFL染料分子的激发态注入; 第二, 从电荷转移复合物(5(6)CFL/TiO₂)直接注入. 时间分辨荧光光谱表明, 在水溶液中纯5(6)CFL染料的荧光以寿命为τ₁=41 ps (74.4%) 和τ₂=3.22 ns (25.6%) 的双e指数衰减, 而5(6)CFL染料敏化TiO₂纳米粒子体系的荧光分别以时间常数为τ₁=44 ps (90.4%), τ₂=478 ps (8.6%) 和τ₃=2.41 ns (1.0%) 的三e指数衰减. 本文的研究工作能够为染料敏化太阳能电池的光致电子转移机理提供有价值的参考.     

Theoretical and experimental investigations of coherent phonon dynamics in sapphire crystal using femto- second time-resolved coherent anti-Stokes Raman scattering

We report on the theoretical and the experimental investigations of the coherent phonon dynamics in sapphire crystal using the femtosecond time-resolved coherent anti-Stokes Raman scattering (fs-CARS) technique. The temporal chirped white-light continuum (WLC) is used for the Stokes pulse, therefore we can perform the selective excitation of the phonon modes without using a complicated laser system. The expected quantum beat phenomenon is clearly observed. The theoretical formulas consist very well with the experimental results. The dephasing times of the excited phonon modes, the wavenumber difference, and the phase shift between the simultaneously excited modes are obtained and discussed. This work opens up a way to study directly high-frequency coherent phonon dynamics in bulk crystals on a femtosecond time scale and is especially helpful for understanding the nature of coherent phonons.     

Scanning the energy dissipation process of energetic materials based on excited state relaxation and vibration–vibration coupling

The energy dissipation mechanism of energetic materials(EMs) is very important for keeping safety. We choose nitrobenzene as a model of EM and employ transient absorption(TA) spectroscopy and time-resolved coherent anti-stokes Raman scattering(CARS) to clarify its energy dissipation mechanism. The TA data confirms that the excited nitrobenzene spends about 16 ps finishing the twist intramolecular charge transfer from benzene to nitro group, and dissipates its energy through the rapid vibration relaxation in the initial excited state. And then the dynamics of vibrational modes(VMs) in the ground state of nitrobenzene, which are located at 682 cm~(-1)(v_1), 854 cm~(-1)(v_2), 1006 cm~(-1)(v_3), and 1023 cm~(-1)(v_4),is scanned by CARS. It exhibits that the excess energy of nitrobenzene on the ground state would further dissipate through intramolecular vibrational redistribution based on the vibrational cooling of vi and v_2 modes, v_1 and v_4 modes, and v_3 and v_4 modes. Moreover, the vibration-vibration coupling depends not only on the energy levels of VMs, but also on the spatial position of chemical bonds relative to the VM.     

Diffraction of white-light supercontinuum by femtosecond laser-induced transient grating in carbon bisulfide

Experiments on fs laser-induced transient grating (LITG) in carbon bisulfide (CS2 ) are carried out to explore the chirp characteristics of a white-light supercontinuum (SC) generated by a 800-nm, 160-fs laser pulse in a 4-mm thick Al2O3 crystal. Two orders of diffraction signals of SC by fs LITG in CS2 are observed, demonstrating that both the third-order process and the fifth-order process are present simultaneously. The experimental results also imply that the formation of an fs transient refractive-index grating in CS2 is mainly due to the electronic polarization process.     

激发态吸收的简并四波混频

从理论和实验两方面讨论了外泵浦场存在时四能级模型的饱和吸收体激发态简并四波混频过程,结果显示外泵浦场强对激发四波混频信号强度有较大的影响,在外场由小到大的变化过程中,信号强度经历一个由小到大再到小的过程. 关键词：     

六硝基菧溶液的νs(NO2)激发及弛豫过程的相干反斯托克斯拉曼光谱

研究含能材料的振动激发和弛豫过程能深入理解含能材料的超快动态响应过程. 利用亚皮秒分辨的相干反斯托克斯拉曼(CARS)技术,实验直接观察基态的六硝基菧溶液中ν_s(NO₂)激发峰位于1385 cm^-1,弛豫时间为0.38和8.5 ps. 飞秒CARS实验观察到相应的拍频现象.     

Transient grating study of the intermolecular dynamics of liquid nitrobenzene

Femtosecond time-resolved transient grating(TG) technique is used to study the intermolecular dynamics in liquid phase. Non-resonant excitation of the sample by two crossing laser pulses results in a transient Kerr grating, and the molecular motion of liquid can be detected by monitoring the diffraction of a third time-delayed probe pulse. In liquid nitrobenzene(NB), three intermolecular processes are observed with lifetimes of 37.9±1.4 ps, 3.28±0.11 ps, and 0.44±0.03 ps, respectively. These relaxations are assigned to molecular orientational diffusion, dipole/induced dipole interaction, and libration in liquid cage, respectively. Such a result is slightly different from that obtained from OKE experiment in which the lifetime of the intermediate process is measured to be 1.9 ps. The effects of electric field on matter are different in TG and optical Kerr effect(OKE) experiments, which should be responsible for the difference between the results of these two types of experiments. The present work demonstrates that TG technique is a useful alternative in the study of intermolecular dynamics.     

两种新型有机染料的双光子上转换特性研究

通过对两种新型有机染料上转换材料CEASP-Ce与CEASPI的测试,研究了它们的双光子吸收、频率上转换特性.实验利用930 nm的红外激光泵浦两种染料溶液可得到 610 nm左右的上转换荧光.当提高浓度时,会得到方向性好、强度高、窄线宽的放大自发辐射（ASE）.通过对两种染料双光子光谱及上转换效率的比较,考察稀土离子对于有机物双光子上转换过程的影响.     

Structural deformation of nitro group of nitromethane molecule in liquid phase in an intense femtosecond laser field

The structural deformation of NO_2 group induced by an intense femtosecond laser field of liquid nitromethane(NM)molecule is detected by time-and frequency-resolved coherent anti-Stokes Raman spectroscopy(CARS) technique with the intense pump laser. Here, we present the mechanism of molecular alignment and deformation. The CARS spectra and its FFT spectra of liquid NM show that the NO_2 torsional mode couples with the CN symmetric stretching mode and that the NO_2 group undergoes ultrafast structural deformation with a relaxation time of 195 fs. The frequency of the NO_2 torsional mode in liquid NM(50.8±0.3 cm~(-1)) at room temperature is found. Our results prove the structural deformation of two groups in liquid NM molecule occur simultaneously in the intense laser field.     

二甲基亚砜溶剂中All-trans-astaxanthin的拉曼和红外光谱

The Raman and infrared spectra of all-trans-astaxanthin (AXT) in dimethyl sulfoxide (DMSO) solvent were investigated experimentally and theoretically. Density functional cal-culations of the Raman spectra predict the splitting of the υ₁ band into υ_1-1 and υ_1-2 compo-nents. The absence of splitting in Raman experimental spectra is ascribed to the competition between the two symmetric C=C stretching vibrations of the backbone chain. The υ₁ band is very sensitive to the excitation wavelength: resonance excitation stimulates the higher-frequency υ_1-2 mode, and off-resonance excitation corresponds to the lower-frequency υ_1-1 mode. Analyses of the intramolecular hydrogen bonding between C=O and O-H in the AXT/DMSO system reveal that the C4=O1...H1-O3 and C4''=O2...H2-O4 bonds are strengthened and weakened, respectively, in the electronically excited state compared with those in the ground state. This result reveals significant variations of the AXT molecular structure in different electronic states.