J. Voigt  Th. Renger  R. Schdel  Th. Schrtter  J. Pieper  H. Redlin 《physica status solidi b》1996,194(1):333-350

Exciton states and their coupling to long-wavelength protein vibrations are investigated both, experimentally and theoretically, in Chl a/b pigment–protein complexes acting as light-harvesting antennae in higher plants. It is shown that the 12 chlorophyll molecules located within the involved protein-monomers form extended exciton states and act cooperatively in the light absorption process. Besides one-exciton excitations also two-exciton excitations are demonstrated at higher photon densities incident on the monomer clusters resulting in nonlinear transmission and emission effects. The distribution of excitons over the exciton energy levels follows a Boltzmann law as shown by emission and nonlinear transmission experiments. The exciton–vibration coupling is weak as indicated by a resonance-like zero-phonon emission line which shows a strong reabsorption. Conclusions are drawn about the structure–function relationship of this antenna type. Interesting similarities between the biological structure investigated and semiconductors or semiconductor structures are discussed.  相似文献   

    

Th. Lückemeyer  H. Franke 《Applied Physics A: Materials Science & Processing》1992,55(1):41-48

Polymer lightguides of PMMA doped with the azo dyes methyl-red and N, N-dihexyl-4-amino-4'-nitro-azobenzene (DHANA) are investigated with respect to their opto-optical properties. The trans-cis photoisomerisation of the dyes leads to reversible polarization-dependent optically induced refractive index changes. The index changes are anisotropic. Birefringence is measured using index matched lightguides. The changes with respect to each polarization are determined by leaky mode spectroscopy and by using a half-integrated interferometer. These changes are intensity dependent and, with a suitable geometry, bistability at low intensities (3 mW/mm³) can be obtained.  相似文献   

    

D. Lüerssen  R. Bleher  H. Kalt  H. Richter  Th. Schimmel  A. Rosenauer  D. Litvinov  A. Kamilli  D. Gerthsen  B. Jobst  K. Ohkawa  D. Hommel 《physica status solidi (a)》2000,178(1):189-192

Pairs of bright spots aligned parallel to the cleaved sample edges are observed in micro‐photoluminescence intensity maps of ZnSe/ZnMgSSe quantum‐well structures. Structural characterization by atomic‐force microscopy, plan‐view and cross‐section transmission electron microscopy reveal that the enhanced radiative recombination is induced by pairs of stacking faults intersecting the quantum wells. In the case of Frank‐type stacking faults the wells are enlarged by up to 12 bilayers leading to an efficient exciton localization. This localization is much shallower in the case of Shockley‐type stacking‐fault pairs.  相似文献   

    

V.Yu. Timoshenko  V. Duzhko  Th. Dittrich 《physica status solidi (a)》2000,182(1):227-232

Strong retardation of photovoltage transients has been observed in porous materials (meso‐ and nanoporous Si, sintered networks of TiO₂ nanoparticles, porous Al oxide) excited by short laser pulse. It has been shown that the photovoltage is mainly determined by the slow carriers diffusion with different diffusion coefficients for electrons and holes. The influence of particle dimension, sign of more mobile charge carriers, and surface conditioning on the diffusion photovoltage has been demonstrated. We propose the diffusion photovoltage method as a universal technique to study carrier diffusion in materials with very low conductivity.  相似文献   

    

H.E. Porteanu  V.Yu. Timoshenko  Th. Dittrich  F. Koch 《physica status solidi (a)》2000,182(1):201-206

Microwave conductivity and Raman spectroscopy were applied to study the influence of light and thermal annealing on porous TiO₂ properties. Microwave absorption in porous TiO₂ (anatase) showed an anomalous behaviour in the presence of light excitation (at 514 nm, i.e. below, or 356 nm, i.e. above the band gap). Exposure to light at a time scale of minutes reduces the microwave conductivity, in contrast to many bulk semiconductors excited above band gap. A reduced content of oxygen after heating in vacuum leads also to a reduction of microwave absorption. Both observations are in apparent contradiction with dc conductivity in TiO₂. By comparison with light‐induced EPR experiments, we conclude that the oxygen removal creates deep defects to which are transferred electrons previously trapped in shallow donors. As a consequence, this decreases the polarisability of TiO₂ nanoparticles, the microwave absorption, and the dielectric constant.  相似文献   

    

R.V. Vedrinskii  V.L. Kraizman  A.A. Novakovich  Sh.M. Elyafi  S. Bocharov  Th. Kirchner  G. Drger 《physica status solidi b》2001,226(1):203-217

Polarized Ni K XANES of single crystal NiO is studied experimentally and theoretically for two crystal orientations relative to the polarization and wave vectors of incident X‐ray beam. The spectra calculated by the full multiple scattering method for a spin‐dependent cluster potential and incomplete screening of the core hole appear to be in an excellent agreement with the experiment. The low energy pre‐edge peak is shown to be caused by the quadrupole transitions of the Ni 1s electron to an exciton‐type state shifted down by ∼4 eV from the empty e_g high‐energy conduction band under the influence of the core hole potential. The feature caused by the Ni 1s → e_g band dipole transitions is also recognized in the spectrum. It is shown that the same mechanisms, which are responsible for the formation of the pre‐edge fine structure in the oxides of early 3d‐metals in 3d⁰ state, work in the considered case as well. A comparative analysis outlining the significance of different mechanisms for the pre‐edge structure formation in cases of early and late 3d‐metal spectra is presented. The antiferromagnetic order of the absorber is taken into account within one‐electron approximation.  相似文献   

    

B. Czarni‐Matusewicz  Th. Zeegers‐Huyskens 《Journal of Physical Organic Chemistry》2000,13(5):237-243

The mid‐ and near‐IR spectra of hydrogen‐bonded complexes involving pentachlorophenol (PCP) and organic bases (acetonitrile and O‐bases) were investigated in carbon tetrachloride solution. The complex between PCP and acetonitrile (ACN) was studied at different ACN: CCl₄ concentration ratios. The frequency of the simultaneous transition ν(OHN) + ν(CN) depends on this concentration ratio. The anharmonicity of the ν(OHN) vibration is discussed as a function of the Onsager parameter of the medium. The anharmonicity of the ν(OHO) vibration of complexes involving PCP and O‐bases increases with increasing enthalpy of complex formation. Other near‐IR observations are discussed. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

    

R. Scholz  A.Yu. Kobitski  T.U. Kampen  M. Schreiber  D.R.T. Zahn  G. Jungnickel  Th. Frauenheim 《physica status solidi b》2000,221(1):541-544

Epitaxial films of a prototype organic semiconductor, 3,4,9,10‐perylene‐tetracarboxylic‐dianhydride (PTCDA) are investigated with resonant Raman spectroscopy and density functional calculations. It is shown that the resonant Raman spectra are mainly determined by the vibrational properties of an isolated molecule, and the pronounced subbands in the absorption spectra of dissolved PTCDA molecules can be related to elongations of the Raman‐active breathing modes between the ground state and the relaxed excited state.  相似文献   

    

P. Vogt  A. M. Frisch  Th. Hannappel  S. Visbeck  F. Willig  Ch. Jung  N. Esser  W. Braun  W. Richter 《physica status solidi b》1999,215(1):737-742

In this study soft X-ray photoemission spectroscopy (SXPS) and scanning tunneling microscopy (STM) were used to investigate the microscopic structure of the P-rich so-called (2×1) reconstruction of InP(001). The samples were homoepitaxially grown in a commercial MOVPE reactor, transferred to ultra high vacuum (UHV), and then transported to separate UHV analysis chambers. Electron diffraction patterns of the samples taken after transfer show a (2×1)/(2×2) periodicity with streaks in the [1-10] direction. STM images display rows along the [110] direction showing a twofold periodicity. Consistent with SXPS spectra of the P2p and In4d core levels the structure can be explained by a fractional monolayer of P-dimers adsorbed on a complete second layer of P. The P-dimers are arranged in local (2×2)/c(2×2)/c(4×2) structures showing a lack of long-range ordering.  相似文献   

    

O. Goede  W. Heimbrodt  Th. Kpp 《physica status solidi (a)》1988,108(1):443-447

The photoacoustic (PA) spectroscopy using a piezoelectric PZT transducer attached to the sample is shown to be successfully employable also for small gap II–VI semiconductor bulk crystals and epilayers both in the low- and high-absorption region. The PA measurements of CdTe and (Hg, Cd)Te mixed crystals carried out at room temperature yield information about the quality and composition of the samples, respectively. Especially, the PA spectroscopy can be used to study the exciton absorption region of a layer also in the case of a substrate with smaller energy gap, as demonstrated for CdTe epilayers on GaAs as an example.  相似文献