Wang Shu-Feng

Refractive index and extinction coefficient of CH 3 NH 3 PbI 3 studied by spectroscopic ellipsometry

Research concerning CH3NH3PbI3 solar cells (SCs) has attracted great attention. However, the CH3NH3PbI3 material’s critical dispersion relationships, i.e. the refractive index and the extinction coefficient, n(λ) and k(λ), as functions of λ, have been little studied. Without this knowledge, it will be difficult to quantitively investigate the optical properties of the CH3NH3PbI3 SCs. We studied n(λ) and k(λ) of CH3NH3PbI3 with spectroscopic ellipsometry. The CH3NH3PbI3 film was fabricated by dual-source evaporation, and the surface roughness was investigated to facilitate SE modeling. With the acquired n(λ) and k(λ), we applied the finite difference time domain method to calculate the ultimate efficiency, η(d), without considering carrier recombination, of the planar CH3NH3PbI3 SC as a function of the film thickness, d, from 31.25 nm to 2 μm, and compared with those of GaAs, c-Si, and a-Si:H(10%H) SCs. It is demonstrated that, η(d) for CH3NH3PbI3 SC is a little smaller than, but very close to that for the GaAs SC, however, much larger than that for the c-Si SC, for all d calculated; and much larger than that for the a-Si:H(10%H) SC when d > 100 nm. Apart from an appropriate band gap near 1.5 eV, the larger k(λ) and smaller n(λ) of CH3NH3PbI3 explain why the CH3NH3PbI3 SC has high efficiency.

Investigation on ultrafast third-order optical nonlinearity of metal(dmit)2/(mnt)2 charge transfer complexes

We have investigated the transient third-order optical nonlinearity of the solutions of Metal(dmit)2/(mnt)2 salts in acetone by employing femtosecond optical Kerr gate measurement at 830 nm wavelength. An order of enhancement on the second-order hyperpolarizability is found for the above salts with central atoms of Cu and Ni. We have suggested an explanation for the enhancement based on the extension of electronic conjugation by the centring Cu or Ni atom.

Third-Order Harmonic Generation in Atmospheric Air with Focused Intense Femtosecond Laser Pulses

Generation of third-order harmonics at 800 nm of femtosecond laser pulses is studied in neutral atmospheric air and in plasma of optical breakdown in air. Its efficiency is measured at different fundamental laser intensities. A maximum efficiency is observed at the intensity when optical breakdown in atmospheric air starts. The factors that exhibit the main effects on the harmonic generation, including self-focusing in a neutral air and self-focusing in plasma, are discussed. PACS: 42. 65. Jx, 42. 65. Ky

Ultrafast solvation dynamics at internal sites of staphylococcal nuclease investigated by site-directed mutagenesis

Internal solvation of protein was studied by site-directed mutagenesis, with which an intrinsically fluorescent probe, tryptophan, is inserted into the desired position inside a protein molecule for ultrafast spectroscopic study. Here we review this unique method for protein dynamics research. We first introduce the frontiers of protein solvation, site-directed mutagenesis, protein stability and characteristics, and the spectroscopic methods. Then we present time-resolved spectroscopic dynamics of solvation dynamics inside cavities of active sites. The studies are carried out on a globular protein, staphylococcal nuclease. The solvation at sites inside the protein molecule?s cavities clearly reveals characteristics of the local environment. These solvation behaviors are directly correlated to enzyme activity.Solvation is essential for protein activities. To study internal solvation of protein, site-directed mutagenesis is applied. Intrinsic fluorescent probe, tryptophan, is inserted into desired position inside protein molecule for ultrafast spectroscopic study. Here we review this unique method for protein dynamics researches. We introduce the frontiers of protein solvation, site-directed mutagenesis, protein stability and characteristics, and the spectroscopic methods. Then we present time-resolved spectroscopic dynamics of solvation dynamics inside caves of active sites. The studies are carried out on a globular protein, staphylococcal nuclease. The solvation at internal sites of the caves indicate clear characteristics of local environment. These solvation behaviors correlated to the enzyme activity directly.

Electro-optic and Photorefractive Properties of Doped Poly (N-Vinylcarbazole)

In this work, 100 μm-thick doped poly (N-vinylcarbazole) films with different contents of the electro-optic (EO) chromophore 2,5-dimethyl-4-(p-nitrophenylazo) anisole and plasticizer N-ethylcarbazole were prepared and sandwiched between two indium-tin oxide-covered glass substrates. Their EO measurements and two-beam-coupling experiments were performed by using a single mode (TEM00) He-Ne laser. Both the EO coefficient and the gain for two-beam-coupling were found to be strongly depending on the content of plasticizer.

Investigation of third-order nonlinear optical properties of two azo-nickel chelate compounds

This paper investigates the third-order nonlinear optical properties of two azo-nickel chelate compounds by the optical Kerr gate method at 830nm wavelength with pulse duration of 120 fs. Both of the two compounds exhibited large third-order optical nonlinearity. The second-order hyperpolarizability, γ, of Compound 1 is of 1.0 × 10−31 esu. Due to the charge transfer, the γ of Compound 2 with electron donor and acceptor group is 4.9 × 10−31 esu, which is a four-time enhancement in comparison with Compound 1. The absorption spectra show that the electron push–pull effect, which induces intramolecular charge transfer, leads to the increased optical nonlinearity.

Spectral and Temporal Properties of Femtosecond White-Light Continuum Generated in H2O

The temporal behaviour and spectral distribution of white-light continuum generation in H2O using a focused intense 800 nm 130 fs Ti:sapphire laser were studied. The results indicated that the white-light continuum spectrally ranged from 1000 to 400 nm, which was mainly attributed to self-phase modulation related to the Kerr effect and ionization. The pulse duration of different spectral components of the generated white-light continuum, which was measured with the frequency up-conversion technique, was obtained around 137 fs. It revealed a comparable time resolution as the original laser pulse.

Steady State and Time-Resolved Fluorescence Dynamics of Triphenylamine Based Oligomers with Phenylene/Thiophene/Furan in Solvents

We investigate the photo-physical properties of a series of triphenylamine-based oligomers by steady-state and picosecond transient fluorescence measurements in solvents. The oligomers are composed alternatively with triphenylamine and phenylene/thiophene/furan group, bridged by vinyl group (PNB/PNT/PNF). Their fluorescence spectra show bathochromic phenomenon with solvent polarity and viscosity increasing. The fluorescence decays are bi-exponential for PNB and PNT, and tri-exponential for PNF in THF and aniline. The strong viscosity dependence suggests conformational relaxation along the PNF chain after photo excitation.

Self-organization of CdS nanoparticles in polystyrene film

Self-organization of nano-CdS particles in polystyrene can be observed by encapsulating the particles with n-dodecyl mercaptan owing to a strong electron transfer interaction between the modified CdS nanoparticles and aliphatic carbons in polystyrene. Consequently, ultraviolet/visible absorption edge of the treated nano-CdS/polystyrene composites is further blueshifted in addition to the shift caused by the quantum size effect, and the fluorescence emission peak of the composite becomes redshifted and narrow.

Solvation dynamics of methanol investigated by femtosecond time-resolved fluorescence up-conversion technique

The solvation dynamics of methanol has been investigated using a femtosecond time-resolved fluorescence up-conversion technique. Transient fluorescence spectra of Coumarin 152A dissolved in methanol at different time were reconstructed from the measured fluorescence decays. The Stokes shift was obtained and the solvent response function Sv(t) was fitted using a bimodal function with a fast Gaussian component and a slow bi-exponential component. The Gaussian component was attributed to the effect of free streaming motion of the solvent molecules, whereas the bi-exponential component was caused by the rotational diffusion motion of the solvent molecules. A comparison of our results with reported data was made.