Fuli Zhao

Large area uniform nanostructures fabricated by direct femtosecond laser ablation

An approach for fabricating large area uniform nanostructures by direct femtosecond (fs) laser ablation is presented. By the simple scanning technique with appropriate irradiation conditions, arbitrary size of uniform, complanate nano-grating, nano-particle, and nano-square structures can be produced on wide bandgap materials as well as graphite. The feature sizes of the formed nanostructures, which can be tuned in a wide range by varying the irradiation wavelength, is about 200 nm with 800 nm fs laser irradiation. The physical properties of the nano-structured surfaces are changed greatly, especially the optical property, which is demonstrated by the extraordinary enhancement of light transmission of the treated area. This technique is efficient, universal, and environmentally friendly, which exhibits great potential for applications in photoelectron devices.

Spectral properties and effective upconverted lasing of new organic molecules

Abstract A series of new organic molecules with high efficiency for two-photon-pumped lasing have been synthesized in this work. Ultrafast spectroscopy demonstrates very fast emission dynamics in this kind of compound, which is an important characteristic for their application. It results in an efficiency of upconverted amplified spontaneous emission (ASE) up to 12.6% at the pumping of a picosecond laser.

Studies on the energy transfer among the rod-core complex from phycobilisome of Anabaena variabilis by time resolved fluorescence emission and anisotropy spectra

Abstract Picosecond time-resolved fluorescence emission and polarization spectra were recorded for the rod-core complex ( α β ) 6 PC L RC 27 ( α β ) 3 AP L C 8.9 from cyanobacterium Anabaena variablis . Fluorescence decay was measured by single-photon timing and resolved to kinetic components by global data analysis with two different excitation wavelengths at 580 nm and 640 nm. Fluorescence anisotropies were recorded and analyzed at different excitation/emission pairs, such as, 590 nm/625 nm, 625 nm/640 nm, 635 nm/652 nm and 650 nm/665 nm. It was expected through this work to investigate the energy transfer processes between C-PC and APC, as well as those in a C-PC hexamer. Our data indicated that the rod-core complex acted as a functional entity with respect to excitation energy transfer. The kinetic component of 18 ps, observed with excitation at 580 nm and 640 nm, was interpreted as the excitation energy transfer from the three β 84 chromophores of terminal C-PC trimer to an α 84 chromophore in the APC core. The 55 ps component, observed with excitation at 580 nm, most likely represent the transfer from β 155 -PCB to β 84 -PCB in a C-PC monomer. The component of 110 ps, observed with excitation at 640 nm, may originate from the transfer between α 84 - and β 84 -PCB chromophores in a APC monomer. The 10 ps component was assigned to the energy transfer processes between the identical β 155 -PCB or α 84 -PCB chromophores in two trimers while the 40±2 ps and 45 ps components to those among the three β 84 -PCB chromophores in a C-PC trimer and an APC trimer, respectively.

DIRECT MEASUREMENT OF EXCITATION TRANSFER DYNAMICS BETWEEN TWO TRIMERS IN C-PHYCOCYANIN HEXAMER FROM CYANOBACTERIUM ANABAENA VARIABILIS

Abstract We provide the first experimental evidence for the excitation transfers between two trimers of an isolated C-phycocyanin hexamer (αβ) 6 PC L RC 27 , at the end of the rod proximal to the core of PBS in cyanobacterium of Anabaena variabilis , with picosecond time-resolved fluorescence spectroscopy. Our results strongly suggest that the observed fluorescence decay constants around 20 and 10 ps time scales, shown in anisotropy decay, not in isotropic decay experiments arose from the excitation transfers between two trimers via two types of transfer pathways such as 1β 155 ↔6β 155 (2β 155 ↔5β 155 and 3β 155 ↔4β 155 ) and 2α 84 ↔5α 84 (3α 84 ↔6α 84 and 1α 84 ↔4α 84 ) channels and these could be described by Foster dipole-dipole resonance mechanism.

Studies of the Energy Transfer among Allophycocyanin from Phycobilisomes of Polysiphonia urceolata by Time‐Resolved Fluorescence Isotropic and Anisotropic Spectroscopy

Abstract— The excitation energy transfer processes in the allophycocyanin (APC) monomer and trimer from phycobilisomes of Polysiphonia urceolata were studied using picosecond time‐resolved fluorescence isotropic and anisotropic spectroscopy. Based on our experimental results, conclusions could be drawn as follows: (1) After the processes of exciton localization are finished, the localized excitation energy on any chromophore can be transferred to the other chromophores due to the weak couplings between them, and the processes among three p84‐phycocyaninbilin (PCB) chromophores in the center of the ring shape of the APC trimer are more important than those of between a84‐ and p84‐PCB chromophores in the same monomer. (2) The decay time constants of 95 ± 5 ps and 40 ± 5 ps components, observed by us in this work, were assigned to the excitation energy transfer or redistribution between α84‐ and β84‐PCB chromophores in the same monomer of the APC trimer and among three β84‐PCB chromophores in the center of the ring shape of the APC trimer, respectively. Specifically, the assignment of the decay constants for the 40 ± 5 ps component was different from those of previous results. (3) Based on the model of Debreczeny, and using the fluorescence residual anisotropy r(∞) with a probing wavelength of 650 nm, the angles between the C3 symmetry axis and transition dipoles of α84‐ and ‐PCB chromophores were found to be φa84= 67° and φβ84= 148°, respectively, which are in agreement with the prediction of the X‐ray crystal structure of APC. (4) The results show that anisotropy decays, observed with the APC trimer, did exhibit a strongly probing wavelength dependence that did not show up in the monomer.

ENERGY TRANSFER IN ALLOPHYCOCYANIN HEXAMER FROM ANABAENA VARIABILIS BY TIME-RESOLVED SPECTROSCOPY

Abstract The process and mechanism for energy transfer in an allophycocyanin hexamer from Anabaena variabilis have been studied by time-resolved fluorescence spectroscopy. Deconvolution of isotropic time-resolved fluorescence spectra shows that the energy transfer time between two allophycocyanin trimers is about 14 ps, while the energy transfer time from the linker polypeptide (L cm 42 ) to the final emission is about 65 ps. The anisotropic results of time-resolved fluorescence spectra show that the energy transfer process among three ring-like ( α - 84 / α - 84 ) chromophore pairs still plays an important role with a time constant of about 45 ps. The facts support the idea that the mechanism for energy transfer in the allophycyanin hexamer should be described by Foster dipole—dipole interaction rather than by an exciton interaction.

Excitation energy-transfer processes between two trimers in C-phycocyanin hexamer from the cyanobacterium Anabaena variabilis. Investigation by group theory and time-resolved fluorescence spectroscopy

Abstract We have employed group theory and picosecond time-resolved fluorescence isotropy and anisotropy spectroscopy methods to explore the excitation transfers within an isolated C-phycocyanin (C-PC) hexamer (αβ) 6 PC L 27 RC , situated at the end of the rod proximal to the core of the pycobilisome (PBS) in the cyanobacterium Anabaena variabilis . The group-theory results imply that excitation energy transfer between two trimers occurs between the lowest exciton level of each trimer. The excitation energy-transfer process might occur at a rate of 10–20 ps, and it may be described by an exciton hopping-like Forster transfer mechanism. Dynamic components of 45–50 ps are assigned to the excitation transfer from β 155 -PCB chromophores to the exciton states of dimers, which consist of two neighbouring monomers of the same trimer in an isolated C-PC hexamer.

Model of chromophore coupling in allophycocyanin aggregation

A new model is proposed to study the interaactions among chromphores in APC trimer. Using this model, the electronic transition frequencies are calculated. The results are in good agreement with the experimental.

Time-resolved excitation density dependent fluorescence of R-phycoerythrin single crystal

Abstract The fluorescence kinetics of a new single crystal, R-phycoerythrin (R-PE), has been studied by picosecond laser spectroscopy. An excitonic band, which is much more narrow than that of the molecular fluorescnece, is observed. At high pump density, superradiance of excitons in the bulk pure single crystal is recorded. The experimental results of fluorescence kinetics and exciton superradiance of R-PE crystal demonstrate that exciton energy transfer is natural, effective and rapid. It is concluded that excitons play an important role in energy transfer in the antennae of photosynthetic systems.

Ultrafast emission of nanodiamond powder

The ultrafast emission of nanodiamond powder has been detected with ultrafast fluorescence spectroscopy. The ultrafast emission spectrum has been deconvoluted by the Monte-Carlo method and the results show 2 fast decays as 60ps and 350ps, with weighting about 80 percent and 20 percent of the whole emission intensity respectively. Such fast emission has not been detected under the same experimental condition for the samples of pure and defected bulk diamonds. The reason for such ultrafast process has been discussed.