Guo Li-Jun

Correlation of Lithium Ionic Diffusion with Nb Concentration in Li7−xLa3Zr2−xNbxO12 Evaluated by an Internal Friction Method

Solid lithium-ion conductors Li7−xLa3Zr2−xNbxO12 (x = 0.25, 0.5, 1, 1.5) with cubic garnet structure are successfully prepared by a solid state reaction method, and the effects of Nb concentration on lithium ion diffusion are investigated by means of internal friction (IF) technique. A prominent relaxation-type IF peak (actually composed of two components) is observed in each Nb doped Li7La3Zr2O12 compound: with apeak PL at lower temperature and a peak PH at higher temperature. The mechanisms of the two components are suggested to be associated with two diffusion processes of lithium ions via vacancies: 48g ↔ 48g and 48g ↔ 24d. The relaxational strength of the IF peak gradually decreases, which is accompanied by the activation energy increasing from 0.45 eV to 0.64 eV with the increasing Nb doping level. The corresponding mechanism is ascribed to originate from lattice contraction as well as the lower concentration of diffusion ions induced by the substitution of Zr4+ by Nb5+.

Energy Transfer Pathways in Reaction Centre upon Femtosecond Excitation of Accessory Bacteriochlorophylls

The energy transfer pathways from the excited accessory bacteriochlorophylls (B*) within native and modified (pheophytin-exchanged) reaction centres isolated from Rhodobacter sphaeroides (RS601) have been investigated by using the femtosecond pump-probe technique. For native RS601, B* decays with a time constant of 240 fs, followed by a partial recovery of the ground-state bleaching with a timescale of about 2 ps. In modified RS601(Phe), however, B* decays with a time constant of 800 fs for magic angle (54.7°) polarization configuration. In addition to the general assumption of energy transfer pathway from B* to the special pair P, an alternative pathway for energy transfer probably operates as well.

Energy Transfer in Isolated LHC II Studied by Femtosecond Pump-Probe Technique

Excitation energy transfer in the isolated light-harvesting chlorophyll (Chl)-a/b protein complex of photosystem II (LHC II) was studied by the one-colour pump-probe technique with femtosecond time resolution. After exciting Chl-b by 638 nm beam, the dynamic behaviour shows that the ultrafast energy transfer from Chl-b at positions of B2, B3, and B5 to the corresponding Chl-a molecules in monomeric subunit of LHC II is in the time scale of 230 fs. While with the excitation of Chl-a at 678 nm, the energy transfer between excitons of Chl-a molecules has the lifetime of about 370 fs, and two other slow decay components are due to the energy transfer between different Chl-a molecules in a monomeric subunit of LHC II or in different subunits, or due to change of molecular conformation.

Photoinduced Charge Transfer in MBB-PPV/C60 Composite Film

The photoconductive properties of MBB-PPV/C60 composite films fabricated by the physical jet deposition (PJD) technique have been studied on the basis of the photoinduced charge transfer process. Under the photoexcitation, the transverse photoconductivity of the composite films is greatly enhanced by 4 orders of magnitude due to the efficient excitation transfer process from MBB-PPV (as donor) to C60 (as acceptor) occurring at the interface, the separation of charges and the existence of in-layer free carriers. The results indicate that the conjugated polymer/fullerene composite films optimized by an appropriate configuration have potential applications in photoelectric devices and photonic fields.