Metal sulfide coated multiwalled carbon nanotubes synthesized by an in situ method and their optical limiting properties.

A metal sulfide such as ZnS, CdS, Ag(2)S or PbS was coated on the sidewall of multiwalled carbon nanotubes (MWCNTs) by an in situ wet chemical synthesis approach via noncovalent functionalization of MWCNTs with a polyelectrolyte (polyethylenimine or poly(diallyldimethylammonium chloride)) without causing significant electronic and structural modification of the carbon nanotubes. Extensive characterizations of the fabricated nanocomposites have been performed using x-ray diffraction, transmission electron microscopy (TEM), high resolution TEM, energy dispersive x-ray spectroscopy, selected area electron diffraction, thermal gravimetric analysis, Fourier transform IR spectra, UV-vis spectra and x-ray photoelectron spectroscopy. The coating layers were composed of metal sulfide nanoparticles with a mean size of less than 10 nm. The optical limiting property measurements for some metal sulfide coated MWCNTs were carried out by the open-aperture z-scan technique. The results demonstrate that the samples suspended in water showed optical limiting behavior better than that of purified MWCNTs.

[Study on absorption spectra and optical limiting properties of soluble polymer/multi-walled carbon nanotube composites].

Three kinds of soluble polymer grafted multi-walled carbon nanotubes (MWNTs), including poly(N-vinylcarbazole)-MWNTs (MWNTs-PVK), polystyrene-MWNTs (MWNTs-PSt) and poly(methyl methacrylate)-MWNTs (MWNTs-PMMA) were synthesized. The TEM images of these samples show that polymers are coated outside the carbon nanotubes. The UV-Vis absorption spectra of the samples in CHCl3 were taken on a HP8452 spectrophotometer at room temperature. Compared with that of MWNTs suspension, there is a characteristic absorption peak in the ultraviolet region, which can be attributed to the polymers linked covalently with MWNTs. Their nonlinear optical properties and optical limiting (OL) performances were investigated by Z-scan method with 527 nm nanosecond laser pulses. These MWNTs dissolved in chloroform possess similar optical limiting properties, which are better than that of raw MWNT suspension and C60 in toluene solution. Nonlinear refraction, nonlinear absorption and nonlinear scattering mechanism were taken into consideration for explaining the observed results. The analysis of the experimental results shows that nonlinear absorption is the dominant mechanism behind the OL performance of these samples.

[Transient dynamics of excited states and nonlinear optical properties of InP nanoparticles].

The decay curves of the emission at different wavelength were measured. One nanosecond of transition lifetime of interband was obtained. The transient dynamics of InP nanoparticles was investigated by one color femtosecond pump-probe method at the wavelength of 800 nm. The experimental result shows that the saturation of exciton resonance results in photobleaching at 800 nm The decay process of the bleaching includes two components, i.e. the fast one from free carries scattering and the slow one from trapped carriers scattering. The nonlinear optical properties of InP nanoparticles were investigated by using femtosecond optical Kerr effect. The magnitude of chi3 for InP nanoparticles embedded in SiO2 sol-gel glass was calculated, and its origin was analyzed.

Dynamics of primary events in the photocycle of excited bacteriorhodopsin.

Transient dynamic behavior of the excited bacteriorhodopsin (BR), which was isolated from the strain H. salinarum, was studied at excitation wavelength from 585 to 639 nm. With the one-color femtosecond (fs) pump-probe technique, we revealed the primary events in BR's photocycle that took place in an ultrafast time scale. From the analysis of the decay components of the dynamical traces, it was evident that the isomerization of the retinal chromophore in BR and the intermediate J's formation occurred within 500 fs. BR exhibited pH-dependent dynamical behaviors. When the medium pH was between 5 and 9, the BR ultrafast dynamics has no obvious change. In contrast, the dynamical curves were obviously affected when the pH was out of that region.

[The charge transfer process of PAN-C60 copolymer films by time-resolved fluorescence spectra].

The charge transfer (CT) process in PAN-C60 copolymer films was studied by absorption and picosecond time-resolved photoluminescence (TRPL) spectra. The CT process can be confirmed from the appearing of new absorption bands and fluorescence quenching of pure PAN in the copolymer films. The TRPL result revealed that excitation state relaxation obeyed biexponential decay process, which were 160 ps and 1,500 ps for the fast and slow decay process, respectively. The fast decay process results from the interaction of chains in the polymer, and a slow decay process comes from the singlet excition recombination. In the copolymer, the singlet excition state lifetime of PAN becomes shorter due to CT process between PAN and C60, which lead to PL quenching of PAN. Additionally, C60 molecules also affect the interchain interaction of PAN by its spacial shape, which closely relates with the fast decay process.

The Ultrafast Energy Transfer Process in Purple Bacteria Photosynthetic Reaction Center.

The ultrafast energy transfer process, which takes place in femtosecond time range, in bacterial photosynthetic reaction center RS601 was investigated using femtosecond pump-probe technique with selective excitation. Upon 755 nmexcitation, the excited state of bacteriopheophytin H decayed to bacteriochlorophyll B with a time constant of about 130 fs, while the excited state of B transported the energy to its energy acceptor, the dimeric bacteriochlorophyll P, in about 240 fs with the 800 nm excitation. The internal conversion process between the upper and lower exciton levels of special pair P might exist upon the excitation of 850 nm pulses. In addition, from the results obtained in our experiments, the charge separation and electron transfer from P to the acceptor H was also observed via the real intermediate B within a few picoseconds.