Search results for "Exciton"
showing 10 items of 317 documents
Molecular structures of chlorophyll a aggregates: spectroscopic and molecular modeling study
1993
Molecular structures of chlorophyll a aggregates have been studied. Spectroscopic properties of these aggregates have been studied by absorption and fluorescence spectroscopy in hydrocarbon solution at various temperatures. Observed spectroscopic shifts were interpreted in terms of simple exciton theory. Exciton splittings were estimated from computer optimized models of previously suggested Chl a aggregate structures.
Refinement of a structural model of a pigment-protein complex by accurate optical line shape theory and experiments.
2007
Time-local and time-nonlocal theories are used in combination with optical spectroscopy to characterize the water-soluble chlorophyll binding protein complex (WSCP) from cauliflower. The recombinant cauliflower WSCP complexes reconstituted with either chlorophyll b (Chl b) or Chl a/Chl b mixtures are characterized by absorption spectroscopy at 77 and 298 K and circular dichroism at 298 K. On the basis of the analysis of these spectra and spectra reported for recombinant WSCP reconstituted with Chl a only (Hughes, J. L.; Razeghifard, R.; Logue, M.; Oakley, A.; Wydrzynski, T.; Krausz, E. J. Am. Chem. Soc. U.S.A. 2006, 128, 3649), the "open-sandwich" model proposed for the structure of the pig…
Excitonic energy level structure and pigment-protein interactions in the recombinant water-soluble chlorophyll protein. II. Spectral hole-burning exp…
2011
Persistent spectral hole burning at 4.5 K has been used to investigate the excitonic energy level structure and the excited state dynamics of the recombinant class-IIa water-soluble chlorophyll-binding protein (WSCP) from cauliflower. The hole-burned spectra are composed of four main features: (i) a narrow zero-phonon hole (ZPH) at the burn wavelength, (ii) a number of vibrational ZPHs, (iii) a broad low-energy hole at ~665 and ~683 nm for chlorophyll b- and chlorophyll a-WSCP, respectively, and (iv) a second satellite hole at ~658 and ~673 nm for chlorophyll b- and chlorophyll a-WSCP, respectively. The doublet of broad satellite holes is assigned to an excitonically coupled chlorophyll dim…
Excitonic Energy Level Structure and Pigment−Protein Interactions in the Recombinant Water-Soluble Chlorophyll Protein. I. Difference Fluorescence Li…
2011
Difference fluorescence line-narrowing spectroscopy at 4.5 K was employed to investigate electron-phonon and electron-vibrational coupling strengths of the lower exciton level of water-soluble chlorophyll-binding protein (WSCP) from cauliflower reconstituted with chlorophyll a or chlorophyll b, respectively. The electron-phonon coupling is found to be moderate with integral Huang-Rhys factors S in the order of 0.81-0.85. A weak dependence of S on excitation wavelength within the inhomogeneously broadened fluorescence origin band is attributed to a sizable contribution of nonresonant excitation that varies with excitation wavelength. The strongly asymmetric and highly structured one-phonon p…
Evidence of delocalized excitons in amorphous solids
2010
We studied the temperature dependence of the absorption coefficient of amorphous ${\mathrm{SiO}}_{2}$ in the range from 8 to 17.5 eV obtained by Kramers-Kronig dispersion analysis of reflectivity spectra. We demonstrate the main excitonic resonance at 10.4 eV to feature a close Lorentzian shape redshifting with increasing temperature. This provides a strong evidence of excitons being delocalized notwithstanding the structural disorder intrinsic to amorphous ${\mathrm{SiO}}_{2}$. Excitons turn out to be coupled to an average phonon mode of 83 meV energy.
Possible mechanism of energy storage in optically stimulable materials: doped alkali halides
1997
Radiation-induced effects in doped alkali halides, mainly in KBr:In, are studied by the luminescence technique. The activator luminescence during a 10 s under UV-light or electron irradiation and, after it, the pulsed photostimulated luminescence on a phosphorescence background were investigated. The obtained results allow us to conclude that the main host lattice excitation relevant to both the luminescence processes mentioned above is a very mobile excitonic excitation including a photon phase and the self- trapped exciton in its composition. The photon phase, as we suppose, represents a free exciton luminescence at room temperature. In this phase, via multiple reabsorption in the low-ene…
<title>Computer modeling of point defects, polarons, excitons, and surfaces in perovskite ferroelectrics</title>
2003
We review results of our recent large-scale computer simulations of point defects, excitons and polarons in ABO3 perovskite crystals, focusing mostly on KNbO3 and KTaO3 as representative examples. We have calculated the atomic and electronic structure of defects, their optical absorption and defect-induced electron density redistribution. The majority of results are obtained using the quantum chemical method of the intermediate neglect of differential overlap (INDO) based on the Hartree-Frock formalism. The main findings are compared with results of ab initio Density Functional Theory (FP-LMTO) first-principles calculations. The results of the electronic structure calculations for different…
Exciton recombination dynamics in InAs∕InP self-assembled quantum wires
2005
In this work we investigate the exciton recombination dynamics in InAs∕InP semiconductor self-assembled quantum wires, by means of continuous wave and time resolved photoluminescence. The continuous wave photoluminescence results seem to indicate that the temperature quenching of the emission band seems to be more probably due to unipolar thermal escape of electrons towards the InP barrier. On the other hand, the analysis of time resolved photoluminescence reveals that the temperature dependence of the radiative and nonradiative recombination times is mainly determined by the dynamics of excitons localized by disorder (high energy tail of the PL band) and strongly localized (low energy tail…
Monte Carlo simulation approach for a quantitative characterization of the band edge in InGaN quantum wells
2005
Monte Carlo simulation approach based on exciton hopping through randomly distributed localized states is proposed for quantitative characterization of the band edge of InxGa1–xN/GaN multiple quantum wells with different indium content (x ≈ 0.22–0.27). The band edge dynamics is investigated in the 10–300 K range by analyzing the measured S- and W-shaped temperature behavior of the photoluminescence peak position and linewidth, respectively. The simulation of the W-shaped temperature dependence using double-scaled potential profile model enabled us to estimate the scale of the potential fluctuations due to variation of indium content inside and among In-rich regions formed in InGaN alloy. In…
Photoluminescence from strained InAs monolayers in GaAs under pressure
1994
bulk GaAs. At pressures above the band crossover two emission bands are observed. These bands, characterized by having negative pressure coefBcients, are attributed to the type-I transition between conduction-band X „and heavy-hole states of the InAs monolayer and the type-II transition &om X states in GaAs to InAs heavy-hole states. The results are interpreted in terms of tight-binding band-structure calculations for the strained InAs-monolayer — bulk-GaAs system. I. INTRODUCTION Highly strained InAs jGaAs heterostructures have recently attracted interest due to their unusual electronic and optical properties. ~ 4 Epitaxial isomorphic growth of InAs on GaAs can be achieved only up to a sma…