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1. Scanning Near-Field Optical Spectroscopy of Quantum-Confined Semiconductor Nanostructures

Author

Colocci, M., Emiliani, V., Gucciardi, P. G., Kudrna, J., Vinattieri, A., Beig, R., editor, Englert, B. -G., editor, Frisch, U., editor, Hänggi, P., editor, Hepp, K., editor, Hillebrandt, W., editor, Imboden, D., editor, Jaffe, R. L., editor, Lipowsky, R., editor, v. Löhneysen, H., editor, Ojima, I., editor, Sornette, D., editor, Theisen, S., editor, Weise, W., editor, Wess, J., editor, Zittartz, J., editor, Watanabe, Yoshio, editor, Salviati, Giancarlo, editor, Heun, Stefan, editor, and Yamamoto, Naoki, editor

Published
2002
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9. Optical properties and photoexcitations of an organic blue emitter embedded in a polymeric active matrix.

Author

Giovanella, U., Botta, C., Gurioli, M., Papagni, A., Tubino, R., Maiorana, S., Del Buttero, P., Alderighi, D., and Kudrna, J.

Subjects
CARBAZOLE, PHOTOLUMINESCENCE
Abstract

The doping of a widely used active polymeric matrix, the polyvinyl carbazole (PVK), with an organic blue emitter has been studied by both continuous wave and time resolved photoluminescence spectroscopy. It is found that the overall emission efficiency of the blend is controlled by two processes: the resonant transfer from the donor to the acceptor and the hopping between the donor sites. Because of the observed spectral variations of the emission spectrum of PVK (donor) with the temperature, both processes exhibit a strong, albeit opposite temperature dependence. The existence of the hopping process accounts for the sharp increase of the transfer efficiency with the concentration, not predicted by the Foerster theory. [ABSTRACT FROM AUTHOR]

Published
2002
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11. Optical properties and photoexcitations of an embedded in a polymeric active matrix

Author

Giovanella, U, Botta, C, Gurioli, M, Papagni, A, Tubino, R, Maiorana, S, Del Buttero, P, Alderighi, D, Kudrna, J, Kudrna, J., PAPAGNI, ANTONIO, TUBINO, RICCARDO, Giovanella, U, Botta, C, Gurioli, M, Papagni, A, Tubino, R, Maiorana, S, Del Buttero, P, Alderighi, D, Kudrna, J, Kudrna, J., PAPAGNI, ANTONIO, and TUBINO, RICCARDO

Abstract

The doping of a widely used active polymeric matrix, the polyvinyl carbazole (PVK), with an organic blue emitter has been studied by both continuous wave and time resolved photoluminescence spectroscopy. It is found that the overall emission efficiency of the blend is controlled by two processes: the resonant transfer from the donor to the acceptor and the hopping between the donor sites. Because of the observed spectral variations of the emission spectrum of PVK (donor) with the temperature, both processes exhibit a strong, albeit opposite temperature dependence. The existence of the hopping process accounts for the sharp increase of the transfer efficiency with the concentration, not predicted by the Foerster theory. © 2002 American Institute of Physics.

Published
2002

29. Electroluminescent properties of a-SiOx:H alloys

Author

Knápek, P., primary, Luterová, K., additional, Pelant, I., additional, Fejfar, A., additional, Kočka, J., additional, Kudrna, J., additional, Malý, P., additional, Janssen, R., additional, and Stutzmann, M., additional

Published
1998
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37. Fast Energy Transfer and Exciton Dynamics in Chlorosomes of the Green Sulfur Bacterium Chlorobium tepidum

Author

Psencik, J., Polivka, T., Nemec, P., Dian, J., Kudrna, J., Maly, P., and Hala, J.

Abstract

The excited-state structure and energy-transfer dynamics, including their dependence on temperature and redox conditions, were studied in chlorosomes of the green sulfur bacterium Chlorobium tepidum at low temperatures by two independent methods:  spectral hole burning in absorption and fluorescence spectra and isotropic one-color pump−probe spectroscopy with ~100 fs resolution. Hole-burning experiments show that the lowest excited state (LES) of BChl c aggregates is distributed within approximately 760−800 nm, while higher excitonic states of BChl c (with absorption maximum at 750 nm) possess the main oscillator strength. The excited-state lifetime determined from hole-burning experiments at anaerobic conditions was 5.75 ps and most likely reflects energy transfer between BChl c clusters. Isotropic one-color absorption difference signals were measured from 720 to 790 nm at temperatures ranging from 5 to 65 K, revealing BChl c photobleaching and stimulated emission kinetics with four major components, with lifetimes of 200−300 fs, 1.7−1.8 ps, 5.4−5.9 ps, and 30−40 ps at anaerobic conditions. The lifetimes are attributed to different relaxation processes of BChl c, taking into account their different spectral distributions as well as limitations arising from results of hole burning. Evidence for at least two spectral forms of BChl c in chlorosome is reported. There is a striking similarity between the spectrum and kinetics of the 5.4−5.9 ps component with those of the LES determined from hole burning. A pronounced change of isotropic decays was observed at around 50 K. The temperature dependence of the isotropic decays is correlated with temperature-dependent changes of BChl c fluorescence emission. Further, the temperature decrease leads to an increase in the relative amplitude of the 200−300 fs component. At aerobic conditions, both hole burning and pump−probe spectroscopy show that the lifetime of the LES shortens to ~2.6 ps, as a result of excitation quenching by a mechanism presumably protecting the cells against superoxide-induced damage. This mechanism operates on at least two levels, the second one being characterized by a 14−16 ps lifetime.

Published
1998

38. Ultrafast Carrier Dynamics in Undoped Microcrystalline Silicon

Author

Kudrna, J., Maly, P., Trojánek, F., Stepanek, J., Lechner, T., Pelant, I., Meier, J., Kroll, U., and Štěpánek, J.

Abstract

We have studied ultrafast dynamics of photoexcited carriers in μc-Si:H by pump and probe laser spectroscopy. We have found that the dynamics of photoexcited carriers in μc-Si:H depend on the crystallinity of the material: in the samples with low crystalline fraction, the dynamics have a fast decay and resemble those in a-Si:H, while in the samples with high crystallinity the dynamics are slower and similar to those in c-Si. We have identified an intensity dependent bimolecular recombination in the samples with lower crystalline fraction (coefficient B = 2×10-10 cm3 s-1 for deposition with silane dilution ratio ≈5% at a fixed power of 6 W), and no bimolecular recombination in the samples with high crystallinity.

41. Ultrafast carrier dynamics in undoped microcrystalline silicon

Author

Kudrna, J., Malý, P., Trojánek, F., Stepánek, J., Lechner, T., Pelant, I., Meier, Johannes, Kroll, U., Kudrna, J., Malý, P., Trojánek, F., Stepánek, J., Lechner, T., Pelant, I., Meier, Johannes, and Kroll, U.

Abstract

We have studied ultrafast dynamics of photoexcited carriers in μc-Si:H by pump and probe laser spectroscopy. We have found that the dynamics of photoexcited carriers in μc-Si:H depend on the crystallinity of the material: in the samples with low crystalline fraction, the dynamics have a fast decay and resemble those in a-Si:H, while in the samples with high crystallinity the dynamics are slower and similar to those in c-Si. We have identified an intensity dependent bimolecular recombination in the samples with lower crystalline fraction (coefficient B=2×10−10 cm3 s−1 for deposition with silane dilution ratio ≈5% at a fixed power of 6 W), and no bimolecular recombination in the samples with high crystallinity.

43. A strategy for constructing aneuploid yeast strains by transient nondisjunction of a target chromosome

Author

Peck Anders T, Pauw Daniel, Miller Elizabeth M, Kinghorn BreAnna, Keller Kirstie E, Kudrna Julie R, Anders Kirk R, Shellooe Christopher E, and Strong Isaac JT

Subjects
Genetics, QH426-470
Abstract

Abstract Background Most methods for constructing aneuploid yeast strains that have gained a specific chromosome rely on spontaneous failures of cell division fidelity. In Saccharomyces cerevisiae, extra chromosomes can be obtained when errors in meiosis or mitosis lead to nondisjunction, or when nuclear breakdown occurs in heterokaryons. We describe a strategy for constructing N+1 disomes that does not require such spontaneous failures. The method combines two well-characterized genetic tools: a conditional centromere that transiently blocks disjunction of one specific chromosome, and a duplication marker assay that identifies disomes among daughter cells. To test the strategy, we targeted chromosomes III, IV, and VI for duplication. Results The centromere of each chromosome was replaced by a centromere that can be blocked by growth in galactose, and ura3::HIS3, a duplication marker. Transient exposure to galactose induced the appearance of colonies carrying duplicated markers for chromosomes III or IV, but not VI. Microarray-based comparative genomic hybridization (CGH) confirmed that disomic strains carrying extra chromosome III or IV were generated. Chromosome VI contains several genes that are known to be deleterious when overexpressed, including the beta-tubulin gene TUB2. To test whether a tubulin stoichiometry imbalance is necessary for the apparent lethality caused by an extra chromosome VI, we supplied the parent strain with extra copies of the alpha-tubulin gene TUB1, then induced nondisjunction. Galactose-dependent chromosome VI disomes were produced, as revealed by CGH. Some chromosome VI disomes also carried extra, unselected copies of additional chromosomes. Conclusion This method causes efficient nondisjunction of a targeted chromosome and allows resulting disomic cells to be identified and maintained. We used the method to test the role of tubulin imbalance in the apparent lethality of disomic chromosome VI. Our results indicate that a tubulin imbalance is necessary for disomic VI lethality, but it may not be the only dosage-dependent effect.

Published
2009
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