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A methodology is described to extract the absorption coefficient spectrum and exciton oscillator strength of GaN layers and GaN/AlGaN quantum wells by analyzing microtransmittance experiments in high-quality, free-standing membranes with thicknesses in the 160–230 nm range. The absorbance of a subwavelength GaN membrane is found to be an oscillating function of its thickness, in keeping with the standing wave effect. We analyze our results using two alternative models including interference effects and extract identical absorption coefficient values. The room-temperature absorption coefficient of bulk GaN membranes at the main exciton peak is found to be 9 × 104 cm−1. In the case of GaN/AlGaN quantum wells, the enhancement and blue shift of the excitonic absorption are observed, as a result of quantum confinement. [ABSTRACT FROM AUTHOR]

Excitonic effects in 1D semiconductors can be qualitatively different from those in higher dimensions. In particular, the Sommerfeld factor, the ratio of the above-band-edge excitonic continuum absorption to free electron-hole pair generation, has been shown to be less than 1 (suppressed) in 1D systems while it is larger than 1 (enhanced) in 2D and 3D systems. Strong continuum suppression indeed exists in semiconducting single-wall carbon nanotubes, a prototypical 1D semiconductor. However, absorption spectra for carbon nanotubes are typically fit with a combination of Lorentzians and a polynomial background baseline with little physical meaning. Here, we performed absorption measurements in aligned single-chirality (6,5) carbon nanotube films. The obtained spectra were fit with our theoretical model obtained by solving the Boltzmann scattering equation involving fifty-nine different types of transitions among three different types of quasiparticles. Specifically, we took into account microscopic interactions between photons, phonons, and excitons, including their dispersions, which unambiguously demonstrated that the background absorption is due to phonon-assisted transitions from the semiconductor vacuum to finite-momentum continuum states of excitons. The excellent agreement we obtained between experiment and theory suggests that our numerical technique can be seamlessly extended to compute strongly out-of-equilibrium many-body dynamics and time-resolved spectra in low-dimensional materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Dilute-nitride GaNSb bulk materials with up to 1.4% nitrogen were grown by molecular beam epitaxy on GaSb substrates. Hall measurements indicate residual hole concentrations of nearly 1019 cm-3 at room temperature, but a decrease to below 1016 cm-3 and a hole mobility of 1300 cm2/V s at 4.5 K for a sample with 0.6% nitrogen. Photoluminescence (PL) and optical absorption measurements demonstrate a bandgap reduction by up to 300 meV with increasing nitrogen incorporation. The experimental absorption spectra are well fit by a functional dependence corresponding to direct allowed optical transitions, and the PL spectra are also consistent with that interpretation. Room temperature carrier relaxation times in the picosecond range are measured using an ultrafast PL upconversion technique. [ABSTRACT FROM AUTHOR]

The evolution of the frequency-dependent absorption spectra for plastoferrites and carbon black-filled ethylene butylacrylate copolymer composites subjected to a uniaxial tension is evaluated using a vector network analyzer as a function of the elongation ratio over the frequency range of 0.3–5 GHz and at room temperature. The absorption spectrum has a double-peaked structure with two broad and symmetrical components. The positions of the lower-frequency peak (1.5 GHz) and the higher-frequency (≅4±0.3 GHz) do not change with extension over the considered range of strain, however, their relative absorption energy changes versus tensile stress can be explained in terms of a Gaussian molecular network model (affine behavior) provided that the elasticity network in the material occurs in a manner that is topologically similar to the elasticity network of a conventional rubber. The sensitivity of the microwave absorption to elongation ratio can be exploited to provide artificially structured materials with tunable electromagnetic properties. [ABSTRACT FROM AUTHOR]

The influence of a perpendicular electric field (F) on the optical properties of simple hexagonal and rhombohedral few-layer graphenes is studied through the tight-binding model. The electric-field-modulated absorption spectra depend on the stacking sequence. The low-energy absorption spectra of simple hexagonal few-layer graphenes exhibit the jumping structures in the absence or presence of an electric field. On the other hand, absorption spectra of rhombohedral few-layer graphenes show discontinuities and sharp peaks at F=0. Besides, the application of F affects the absorption spectra, generates new peaks, and changes peak position and peak height. The frequency of the peak is predicted to be closely associated with the stacking sequences and the field strength. Above all, the predicted absorption spectra could be verified by optical measurements. [ABSTRACT FROM AUTHOR]

An accurate absorption model including Coulomb interaction and Urbach-broadened band edge has been demonstrated for direct bandgap semiconductors. We propose a steep-edged compound Lorentzian line-shape function for modeling the Urbach tail and the line broadening of exciton absorptions. The results of applying this fitting procedure to room-temperature and low-temperature absorption spectra of GaAs, InP, and InAs are presented, and a consistent set of band parameters are extracted. The analytical absorption model is suitable for a complete closed-form Kramers-Kronig transform of the absorption spectrum to obtain the refractive-index spectrum. [ABSTRACT FROM AUTHOR]

The observed Dy3+ ion upconversion luminescence in LiNbO3 crystal heavily codoped with ZnO was spectrally and temporally analyzed by microsecond time-resolved spectrum under 806 nm intense femtosecond laser excitation at room temperature. Absorption spectrum and modified Judd-Ofelt approach were used to investigate its spectroscopic properties. The bright blue and intense yellow emissions are assigned to transitions 4F9/2→6H15/2 and 4F9/2→6H13/2, respectively. It is concluded that the main upconversion mechanism is excited state absorption by pump power dependence in combination with luminescence intensity temporal evolvements. [ABSTRACT FROM AUTHOR]

Solvent effects on the two-photon absorption of a symmetrical diamino substituted distyrylbenzene chromophore have been studied using the density functional response theory in combination with the polarizable continuum model. It is shown that the dielectric medium has a rather small effect both on the bond length alternation and on the one-photon absorption spectrum, but it affects significantly the two-photon absorption cross section. It is found that both one- and two-photon absorptions are extremely sensitive to the planarity of the molecule, and the absorption intensity can be dramatically reduced by the conformation distortion. It has led to the conclusion that the experimentally observed anomalous solvent effect on the two-photon absorption of dialkylamino substituted distyrylbenzene chromophores cannot be attributed to the intrinsic properties of a single molecule and its interaction with solvents. [ABSTRACT FROM AUTHOR]

C6H5SO2 radicals were produced upon irradiation of three flowing mixtures: C6H5SO2Cl in N2, C6H5Cl and SO2 in CO2, and C6H5Br and SO2 in CO2, with a KrF excimer laser at 248 nm. A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to record the time-resolved infrared (IR) absorption spectra of reaction intermediates. Two transient bands with origins at 1087.7 and 1278.2 cm-1 are assigned to the SO2-symmetric and SO2-antisymmetric stretching modes, respectively, of C6H5SO2. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ) predict the geometry and vibrational wave numbers of C6H5SO2 and C6H5OSO. The vibrational wave numbers and IR intensities of C6H5SO2 agree satisfactorily with the observed new features. Rotational contours of IR spectra of C6H5SO2 simulated based on predicted molecular parameters agree satisfactorily with experimental results for both bands. The SO2-symmetric stretching band is dominated by a- and c-type rotational structures and the SO2-antisymmetric stretching band is dominated by a b-type rotational structure. When C6H5SO2Cl was used as a precursor of C6H5SO2, C6H5SO2Cl was slowly reproduced at the expense of C6H5SO2, indicating that the reaction Cl+C6H5SO2 takes place. When C6H5Br/SO2/CO2 was used as a precursor of C6H5SO2, features at 1186 and 1396 cm-1 ascribable to C6H5SO2Br were observed at a later period due to secondary reaction of C6H5SO2 with Br. Corresponding kinetics based on temporal profiles of observed IR absorption are discussed. [ABSTRACT FROM AUTHOR]

The polarized optical absorption spectra of different quaterthiophene single crystals in the energy region of the exciton bands originating from the first molecular transition are reported as measured in the temperatures ranging from 7 to 140 K. The intrinsic higher mobility of the b-polarized 0-0 au exciton both with respect to its replicas and to the a-polarized structures is demonstrated in high quality crystals at the lowest temperatures. The influence of structural disorder on mobility is discussed considering, for the different samples, the measured lineshape and linewidth of the absorption peaks, and the relative lineshift and intensity ratio between the 0-0 au line and its first replica at the lowest temperature. The influence of dynamic disorder is discussed considering the lineshape and linewidth of the measured peaks as a function of temperature for both polarizations in the framework of the exciton-phonon coupling theory. [ABSTRACT FROM AUTHOR]

The intermolecular arrangement in the solid state and the consequences on the optical and photophysical properties are studied on different derivatives of oligophenylenevinylenes by UV/VIS absorption and angular-resolved polarized fluorescence spectroscopy. Unsubstituted distyrylbenzene (DSB) organizes in a herringbone manner, with the long axes of the molecules oriented in parallel, but the short axes almost perpendicular to each other. Fluorinated distyrylbenzene (F12DSB) as well as the DSB:F12DSB cocrystals prefer cofacial π-stacking in the solid state. For all structures, the consequence of the parallel alignment of the transition moments is a strongly blueshifted H-type absorption spectrum and a low radiative rate constant kF. Significant differences are observed for the emission spectra: the perpendicular arrangement of the short axes in DSB crystals leads to only very weak intermolecular vibronic coupling. Hence the emission spectrum is well structured, very similar to the one in solution. For F12DSB and DSB:F12DSB, the cofacial arrangement of the adjacent molecules enables strong intermolecular vibronic coupling of adjacent molecules. Thus, an unstructured and strongly redshifted excimerlike emission spectrum is observed. The differences in the electronic nature of the excited states are highlighted by quantum-chemical calculations, revealing the contribution of interchain excitations to the electronic transitions. [ABSTRACT FROM AUTHOR]

The Cn+ n=7–9 cations were produced by electron-impact ionization of perchloronaphthalene, mass selected, and their electronic absorption spectra in 6 K neon matrices recorded. The linear and cyclic isomers of C7+ and C8+ are detected. Three systems of linear C7+ are observed with origin bands near 770, 332, and 309 nm. The cyclic C7+ shows two transitions near 676 and 448 nm. One system of linear C9+ is observed commencing at 371 nm. Linear C8+ shows five dipole-allowed electronic transitions from the X 2Πg ground state, and the strongest ones have the origin bands at 890.8 and 308.1 nm. Five electronic transitions of cyclic C8+ are also discernible. [ABSTRACT FROM AUTHOR]

The absorption spectrum of N2, just above the first ionization limit, in the region between 125 750 and 126 600 cm-1, is dominated by two broad features which have the appearance of the towers of a “cathedral.” Recently, this energy region has been measured by Sommavilla et al. [J. Phys. B 35, 3901 (2002)] with a resolution of 0.04 cm-1 and an assignment for one of these two bands has been suggested. In order to discuss this assignment, we have solved the coupled-channel Schrödinger equation with the parameters of Spelsberg and Meyer above the v=28 level of the b′ 1∑u+ state for determining the high levels of b′. Furthermore, we evaluate the autoionization widths and the rotational structure of the different possible assignments. Finally, we propose as assignment for the second tower of the cathedral the Rydberg state (A 2Πuv+=1)3′d′σg1Πu. [ABSTRACT FROM AUTHOR]

The steady-state light-induced absorption and the temporal relaxation behavior under illumination of cw ultraviolet light in Mn-doped near-stoichiometric LiNbO3 with different crystal compositions are investigated. The ultraviolet-light-induced absorption has been assigned to small polarons NbLi4+ by measuring the absorption spectra at room temperature. The dependences of relaxation behaviors (time constant and stretching factor) of light-induced absorption on various illumination conditions (intensity, polarization) and temperature are presented, which are very different from those observed in Fe-doped LiNbO3 illuminated with highly intense light pulse, though the temporal relaxation follows the same stretched-exponential decay behavior in both cases. The results are explained reasonably by using the model of distance-dependent electron transition probabilities between localized deep traps and small polarons without any additional assumptions, and discussed to tailor doped near-stoichiometric LiNbO3 crystals for two-color holographic recording with cw laser light. [ABSTRACT FROM AUTHOR]

Optical-absorption and photoluminescence (PL) spectra have been measured on the defect-chalcopyrite-type semiconductor CdGa2Te4 in the 0.9–1.5-eV photon-energy range at temperatures between 11 and 300 K. The temperature dependence of the direct-gap energy of CdGa2Te4 has been determined from the optical-absorption spectra and fit using the Varshni equation and an analytical four-parameter expression developed for the explanation of the band-gap shrinkage effect in semiconductors. The PL spectra show an asymmetric emission band peaking at ∼1.326 eV and a symmetric emission band at ∼1.175 eV at T=11 K, which are attributed to donor-acceptor-pair recombination between exponentially tailed or Gaussian-like donor states and acceptor levels, respectively. A multiple-exponential fit analysis of the PL emission suggests acceptor levels of 50 and 86 meV and a deep donor level of 190 meV, together with an unidentified shallow level of 9 meV. An energy-band scheme has been proposed for the explanation of PL emission observed in CdGa2Te4. [ABSTRACT FROM AUTHOR]

An emission spectrum of hot water with a temperature of about 3000 K is obtained using an oxy-acetylene torch. This spectrum contains a very large number of transitions. The spectrum, along with previous cooler laboratory emission spectra and an absorption spectrum recorded from a sunspot, is analyzed in the 500–2000 cm-1 region. Use of a calculated variational linelist for water allows significant progress to be made on assigning transitions involving highly excited vibrational and rotational states. In particular emission from rotationally excited states up to J=42 and vibrational levels with up to eight quanta of bending motion are assigned. [ABSTRACT FROM AUTHOR]

The temporal behavior of optical response functions (ORFs) reflects the quantum dynamics of an electronic superposition state, and as such lacks a well-defined classical limit. In this paper, we consider the importance of accounting for the quantum nature of the dynamics when calculating ORFs of different types. To this end, we calculated the ORFs associated with the linear absorption spectrum and the nonlinear two-pulse photon-echo experiment, via the following approaches: (1) the semiclassical forward-backward approach; (2) an approach based on linearizing the path-integral forward-backward action in terms of the difference between the forward and backward paths; (3) an approach based on ground state nuclear dynamics. The calculations were performed on a model that consists of a two-state chromophore solvated in a nonpolar liquid. The different methods were found to yield very similar results for the absorption spectrum and “diagonal” two-pulse photon echo (i.e., the homodyne-detected signal at time t=t0 after the second pulse, where t0 is the time interval between the two pulses). The different approximations yielded somewhat different results in the case of the time-integrated photon-echo signal. The reasons for the similarity between the predictions of different approximations are also discussed [ABSTRACT FROM AUTHOR]

We study the relationship between the optical gap and the optical-absorption tail breadth for the case of amorphous gallium arsenide (a-GaAs). In particular, we analyze the optical-absorption spectra corresponding to some recently prepared a-GaAs samples. The optical gap and the optical-absorption tail breadth corresponding to each sample is determined. Plotting the optical gap as a function of the corresponding optical-absorption tail breadth, we note that a trend, similar to that found for the cases of the hydrogenated amorphous silicon and hydrogenated amorphous germanium, is also found for the case of a-GaAs. The impact of alloying on the optical-absorption spectrum associated with a-GaAs is also briefly examined. [ABSTRACT FROM AUTHOR]

The spectroscopic properties of Tm3+ ions in (57-x)PbO–xPbF2–25Bi2O3–18Ga2O3 (mol %) glasses were investigated through measurements of absorption, emission, and lifetime measurements. The PbF2 substitution in this glass system raised the lifetime of the 1.48 μm emission. The lifetime for the 3H4 level was changed from 272 to 416 μs when the PbF2 content increased from x=0 to 15. In a 47PbO–15PbF2–25Bi2O3–18Ga2O3 glass, the phonon-assisted energy transfer involving two phonons with the energy of 550 cm-1 dominated the cross relaxation of the Tm3+: 3H4, 3H6→3F4, 3F4 route in spite of the presence of the overlap between the 3H4→3F4 emission and 3H6→3F4 absorption spectra. As a result, PbO–PbF2–Bi2O3–Ga2O3 glasses were thought to be useful for the S-band optical fiber amplifiers. [ABSTRACT FROM AUTHOR]

Resonance Raman profiles for 14 vibrational modes of betaine-30 in ethanol at room temperature were measured at wavelengths within the first charge-transfer absorption band. The absorption spectrum and resonance Raman profiles were analyzed using time-dependent theory and a Brownian oscillator model modified to account for nonlinear solvent response; i.e., dependence of the solvent reorganization energy on the electronic state of the solute. As in our previous study of betaine-30 in acetonitrile, the solvent reorganization energy for the excited electronic state, determined from resonance Raman spectroscopy, was found to be smaller than that for the ground electronic state, determined from the absorption spectrum. The mode-dependent internal reorganization energies of betaine-30 in ethanol were found to be slightly larger than those of betaine-30 in acetonitrile. Temperature-dependent solvent reorganization energies for the ground electronic state were determined from analysis of the absorption line shape from 279 to 332 K and were found to decrease with increasing temperature. The influence of hydrogen bonding on the solvent and internal reorganization energy of betaine-30 is considered, and the physical basis for nonlinear solvent response is discussed. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A three-dimensional analog of the Merrifield model is proposed to study excitons in solid perylenetetracarboxylic dianhydride (PTCDA). Its relevant parameters are estimated by independent calculations, and finally determined by fitting the experimental absorption and electroabsorption spectra of PTCDA films; the optimum values obtained from the fit correspond well with the calculated values. The results justify description of PTCDA excitons within a one-dimensional model, as proposed in the literature. The calculated spectra are generally in good agreement with the experimental ones, with the exception of the directional properties of the electroabsorption signal. A possible reason for this discrepancy is suggested. Generally, the results highlight the prominent role of charge-transfer excitons in the electroabsorption spectrum of PTCDA by showing the experimental features that are difficult to explain without invoking these states. [ABSTRACT FROM AUTHOR]

The electronic absorption spectra of dithizone were recorded in various solvents and the absorption maxima of the dye were found to be dependent on solvent polarity. The molecule showed two absorption peaks in the visible region, the higher wavelength band was assigned to the keto form and the lower wavelength band is an overlap of the enol and the keto forms. The absorption data fitted well to Kamlet–Abboud–Taft equation. Studies done in a binary mixture of solvents (acetone + i -PrOH and dichloromethane + i -PrOH) showed that the probe molecule tends to form a hydrogen-bonding solvated complex with the more polar solvent. The values of preferential solvation constant (K PS ) were also calculated and it was found that the solute molecule preferentially solvated in i -PrOH. DFT calculations showed that the keto form absorbance occurred at 608 nm and was assigned to n → π* transition. The first-excited state electron densities suggested that the excited state was favorably stabilized in less polar solvents. [ABSTRACT FROM AUTHOR]

Abstract: Absorption spectra and induced fluorescence excitation emission matrices of colored dissolved organic matter were measured in water samples collected along the Atlantic Meridional Transect in different bio-geographic provinces of the Atlantic Ocean from October to November 2010. The highest values of CDOM absorption coefficient at 305nm (a CDOM(305)), were recorded at the continental margins of the English Channel and Patagonian Shelf. The lowest values of a CDOM(305) were observed in the mixed layer of both North and South Atlantic subtropical oligotrophic gyres. The DOM composition was assessed using fluorescence spectroscopy, Excitation Emission Matrix spectra (EEMs) and the Parallel Factor Analysis (PARAFAC) model in addition to spectral indices calculated from CDOM absorption spectrum and EEMs. Six different components were identified in the EEMs by PARAFAC: Two components were similar to the humic-like fraction of DOM, associated with basin scale microbial mineralization processes. These components represent allochthonous DOM in the biogeographic provinces studied. One component of marine humic-like material of autochthonous origin was associated with DOM production from marine phytoplankton. Three components were associated with protein-like DOM. Two protein-like components had the spectral characteristics of pure tryptophan and tyrosine. There was a significant difference in DOM composition both between bio-geographical provinces and above and below the mixed layer. In the mixed layer in all provinces, except the waters of the Western European Shelf, the DOM was dominated by protein-like components. At the Western European Shelf, it was dominated by humic-like components. Fluorescence intensities of humic-like components were high at the Patagonian Shelf, but were up to 40% lower compared to northern hemisphere shelf waters. Humic-like components made a significant contribution to the DOM composition of the upper mesopelagic layer in all provinces, with the highest values at the Equatorial Upwelling Zone. There was a significant inverse relationship between humic-like components and salinity and temperature and a positive relationship with Apparent Oxygen Utilization. The humification index (HIX) was linearly correlated with the intensity of the humic-like DOM components. These trends suggest that the humic-like components are in dynamic equilibrium between likely microbial production in the deep ocean and photochemical degradation in the mixed layer. [Copyright &y& Elsevier]

Abstract: The structure of the radioluminescent (RL) spectrum of Li2B4O7:Cu crystal is complex, having no normal Gauss peaks. The RL spectrum recorded showed one sharp and strong peak near 365nm. For the purpose of explaining this phenomenon, we used the self-trapped exciton (STE) model to analyze experimental data of absorption spectrum, emission spectrum, radioluminescence spectrum and decay-time curves. We found a short lifetime component (of the order of ns) from phosphorous signals of Li2B4O7:Cu. We realized that the short lifetime component related to inherent signal of host lattice and the d–p transitions of Cu+. This result is applicable in the detector system with high time resolution. [ABSTRACT FROM AUTHOR]

New guest-host dyes of red and purple colour suitable for fabrication of ultrathin film polarizer from polymerizable liquid crystals are developed. When the absorption spectrum of dye matches the photopic curve, samples with total film thickness below 50 µm show good visual contrast. [ABSTRACT FROM AUTHOR]

A comparative study of the dispersion of nonlinear absorption in thin films of molecular J- and H-aggregates of polymethine dyes was performed with the use of the Z-scan (Z-scan technique) over the range 625–825 nm under conditions close to resonance absorption at nanosecond duration of excitation. The measurements were made on film samples of J- and H-aggregates prepared by spin-coating and having identical absorption spectra. The H- and J-aggregates were formed by the synthetic thioflavylium DT-3 and benzothiazole BTC18H dyes, respectively. It was found that the samples of different types of aggregates exhibit nonlinear susceptibility of the same order of magnitude with allowance for the width of exciton absorption peaks. [ABSTRACT FROM AUTHOR]

A number of new peaks close to the previously predicted energies of virtual electronic states [S.G. Ovchinnikov and V.N. Zabluda, Zh. Eksp. Teor. Fiz. 125, 150 (2004) [JETP 98, 135 (2004)]] have been observed in the absorption spectra of FeBO3 single crystals in the infrared range. The 0.27-eV peak was absent in the scheme presented in the work cited above and, to explain it, a multielectron theory taking into account the 2 T2 low-spin term of the Fe3+ ion has been developed. [ABSTRACT FROM AUTHOR]

Ni–P/AAO nano-array composite structure assemblies with Ni and P grown in the pores of anodic aluminum oxide (AAO) membranes were prepared by electroless deposition. The results of SEM, TEM and SAED show that as-deposited Ni–P nanowires have an amorphous structure and a few nanocrystallites form after annealing. The optical absorption spectra reveal that, as the annealing temperature increases, the absorption band edge of the Ni–P/AAO composite structure is obviously blue shifted, which is attributed to a decrease of the internal pressure after heat treatment. Meanwhile, the annealed Ni–P/AAO nano-array composite structure exhibits the absorption behavior of a direct band gap semiconductor. Details of this behavior are discussed together with the implications for potential device applications. [ABSTRACT FROM AUTHOR]

Abstract: The photoluminescence, photoconductivity and absorption in GaSe0.9Te0.1 alloy crystals have been investigated as a function of temperature and external electric field. It has been observed that the exciton peaks shift to lower energy in GaSe0.9Te0.1 alloy crystals compared to GaSe crystals. The long wavelength tails of interband photoluminescence, photoconductivity and absorption spectra are determined by the free exciton states and show an Urbach–Martienssen-type dependence to the photon energy. The maxima of the extrinsic photoluminescence and photoconductivity spectra were found to be determined by the acceptor centers with an energy of E A=E V+0.19eV formed by the polytypism and defects complexes that include Se and Te anions. [Copyright &y& Elsevier]

The lowest energy optical electronic absorption band of the three-chromophore system tris(4-bromophenyl)amine radical cation is analyzed. The lowest energy electronic transition corresponds to a p-bromophenyl orbital to nitrogen p orbital transition that places the positive charge on three equivalent p-bromophenyl chromophores. The excited electronic state is an example of excited-state mixed valence (ESMV), and the spectrum is interpreted using two ESMV models. The simplest model invokes the concept of an “effective coupling” between the three identical chromophores with an excited-state energy splitting equal to three times the coupling. A more accurate model, the “neighboring orbital model”, utilizes the coupling between the bridge’s and charge-bearing unit’s orbitals closest in energy. The three-chromophore system provides a striking illustration of the failure of an effective coupling term to account for ESMV splitting. The calculated relative energies of the diabatic and adiabatic states are different, but the calculated absorption spectra of the two models show nearly identical vibrational fine structure. Resonance Raman data and the time-dependent theory of electronic and resonance Raman spectroscopies are used to calculate the spectra. [ABSTRACT FROM AUTHOR]

The energy transfer between two coumarin compounds having donor emission/acceptor absorption spectra overlap was studied firstly in solution by applying an excess of the acceptor. The observed transfer was then confirmed in the bichromophoric compound resulting from the covalent binding of the two fluorophores via a short alkyl chain. [Copyright &y& Elsevier]

Abstract: Two novel, triphenylamine derivatives N-(4-(4-(diphenylamino)styryl)phenyl)acetamide and N-(4-(4-(bis-(4-(4-(diphenyl-amino)styryl)phenyl)amino)styryl)phenyl)acetamide were synthesized. The two-photon absorption of N-(4-(4-(bis-(4-(4-(diphenyl-amino)styryl)phenyl)amino)styryl)phenyl) was ∼17-fold greater relative to N-(4-(4-(diphenylamino)styryl)phenyl)acetamide. Linear absorption spectra, steady-fluorescence and time-resolved fluorescence spectra revealed that electron coupling originating from π-electron delocalization is responsible for the strong cooperative enhancement of TPA within the compounds. This is confirmed by the Lippert-Mataga equation. [Copyright &y& Elsevier]

Results of spectral studies of human liquor aimed at determining the specific features of its composition arising as a result of neurosurgical diseases and during the recovery period are presented. A method for detecting characteristic bands attributed to pathology, which is based on precision measurements of the UV-VIS absorption spectra of liquor and on their subsequent computer analysis is presented. With this method, ironcontaining components of liquor can be qualitatively and quantitatively determined, which is important in solving neurosurgical problems. [ABSTRACT FROM AUTHOR]

The Dy3+ absorption and excitation spectra of BaY2F8 and BaYb2F8 single crystals are investigated in the ultraviolet, vacuum ultraviolet, and visible ranges at a temperature of 300 K. These crystals exhibit intense broad absorption bands due to the spin-allowed 4 f-5 d transitions in the range (56–78) × 10−3 cm−1 and less intense absorption bands that correspond to the spin-forbidden transitions in the range (50–56) × 10−3 cm−1. The Nd3+ absorption spectra of BaY2F8 single crystals are studied in the range (34–82) × 10−3 cm−1 at 300 K for different crystal orientations. [ABSTRACT FROM AUTHOR]

Duan’s simple model is extended to analyze the mixing of the 4 f N − 15 d configuration with the 4 f N states. The explicit static coupling and traditional dynamic coupling are considered, and the parameters are fitted according to the absorption spectrum in LiYF4: Nd3+. The parameter values obtained are as follows: T 32 = −28 i × 10−7, T 52 = −1151 i × 10−7, A = 192 i × 10−12 cm, A = i × 10−12 cm, A = 54 i × 10−12 cm, and A = −680 i × 10−12 cm. Compared to the experimental measurements, the present model yields better results than those obtained from the Judd-Ofelt theory. [ABSTRACT FROM AUTHOR]

Abstract: The role of solute–solvent and solvent–solvent interaction on the preferential solvation characteristics of 2,6-diaminoanthraquinone (DAAQ) has been analysed by monitoring the optical absorption and fluorescence emission spectra. Binary mixtures consist of dimethylformamide (DMF)–ethanol (EtOH), DMF–dimelthylsulfoxide (DMSO), benzene (BZ)–DMF and acetonitrile (ACN)–DMF. The optical absorption spectra maximum and emission spectra maximum of DAAQ show the changes with varying the solvents and change in the composition in the case of binary mixtures. Non-ideal solvation characteristics are observed in all binary mixtures. It is found that at certain concentrations two mixed solvents interact to form a common structure with a ν 12 (wave number in cm−1) value not always intermediate (ν 1 and ν 2) between the values of the solvents mixed. Synergistic effect is observed in the case of DMF–EtOH mixtures. The preferential solvation parameters local mole fraction , solvation index δ S2, exchange constant K 12 are calculated in all binary mixtures expect in the case of DMF–BZ mixture and DMF–EtOH mixture in the ground state. We have also monitored excitation wavelength effect on the probe molecule in aprotic polar and protic polar solvents. [Copyright &y& Elsevier]

We use the millennium Arecibo 21-cm absorption-line survey measurements to examine the issue of the non-thermal contribution to the observed Galactic H i linewidths. If we assume a simple, constant pressure model for the H i in the Galaxy, we find that the non-thermal contribution to the linewidth, scales as , for larger than . Here, l is a derived length-scale and . This is consistent with what one would expect from a turbulent medium with a Kolmogorov scaling. Such a scaling is also predicted by theoretical models and numerical simulations of turbulence in a magnetized medium. For non-thermal linewidths narrower than , this scaling breaks down, and we find that the likely reason is ambiguities arising from Gaussian decomposition of intrinsically narrow, blended lines. We use the above estimate of the non-thermal contribution to the linewidth to determine corrected H i kinetic temperature. The new limits that we obtain imply that a significantly smaller (∼40 per cent as opposed to 60 per cent) fraction of the atomic interstellar medium in our Galaxy is in the warm neutral medium phase. [ABSTRACT FROM AUTHOR]

Abstract: We have performed precise measurements of the transient optical absorption spectra of amorphous (a-) As2Se3 and As2S3 at room temperature in the nanosecond and microsecond domains. From the measurements, we have observed the photodarkening in the nanosecond and microsecond domains for both of the samples. For a-As2Se3, a broad absorption peak in the range from 420 to 730nm was observed. The peak maximum changed to longer wavelength with time. For a-As2S3, a sharp absorption peak in the range from 420 to 510nm and a long absorption tail in the range from 510 to 600nm were observed. The peak maximum does not change with time. Based on the experimental results, we discuss the nanosecond dynamics of the photodarkening in terms of the local structural changes. [Copyright &y& Elsevier]

Abstract: In this paper, we describe new high-resolution measurements of the absorption spectrum of 14NH3 in the 6850–7000cm−1 region using cavity-enhanced absorption spectroscopy (CEAS), and Fourier-transform spectroscopy (FTS) between ∼6400 and 6900cm−1. The CEAS measurements were used to determine line positions, line intensities (cross-sections) and pressure-broadening parameters, the latter in three different bath gases. A total of 1117 NH3 lines were observed. The accuracy of the line positions is about 0.001cm−1, and absorptions cross-sections as low as 1×10−23 cm2 molecule−1 are reported. [Copyright &y& Elsevier]

We have studied the adduct formed by N,N′-2,7-didecyldiazapyrenium (P2+), as the hexafluorophosphate salt, with a third generation dendrimer (D) that comprises 14 tertiary amine units in the interior, and 16 naphthyl and 16 trans-azobenzene units in the periphery. A strong charge-transfer interaction between the electron-accepting diazapyrenium dication and electron-donating amine units of the dendrimer interior leads to a host–guest complex with 1 : 1 stoichiometry, namely D(16t)⊃P2+. The self-assembly process can be easily monitored by strong changes in the absorption and emission spectra: (i) new absorption bands (λmax ≈ 445 and 565 nm) at lower energy compared to the isolated species arise, (ii) a strong quenching of the intense diazapyrenium fluorescence is observed, and (iii) a new broad emission band, typical of the charge-transfer complex, appears with a maximum at 660 nm at 298 K and 600 nm at 77 K. By global analysis of the absorption spectra, an association constant of 1.0 × 106 M−1 is obtained for D(16t)⊃P2+, compared to 3.0 × 104 M−1 in the case of the adduct of P2+ with triethylamine under the same experimental conditions. This result demonstrates that the presence of bulky substituents at the dendrimer periphery does not hinder the formation of a stable complex and suggests a cooperative effect due to the multiple amine groups of the dendrimer branching points. No energy transfer from the azobenzene or naphthyl chromophores to the charge-transfer complex has been evidenced. The self-assembly process can be reversed upon addition of an equimolar amount of trifluoromethanesulfonic acid. An adduct with 1 : 1 stoichiometry is formed also between P2+ and D(2t14c), a species obtained from D(16t) upon irradiation at 365 nm: the corresponding association constant is very similar to that of D(16t)⊃P2+, showing that the isomeric state of the peripheral azobenzene units does not affect the stability of the adduct. [ABSTRACT FROM AUTHOR]

Organic–inorganic nanostructured hybrids based on N, N′-diphenyl- N, N′-bis(3-methylphenyl)-(1,l′-biphenyl)-4,4′-diamine (MTPD) and anatase TiO2 were prepared via layer-by-layer deposition method. The MTPD/TiO2 hybrids were characterized by UV–Vis absorption spectra, photoconductivity measurements, and surface photovoltage spectra (SPS). Due to the change of the aggregated structure caused by the addition of TiO2, MTPD showed blue-shifted absorption spectrum. The photosensitivity of MTPD/TiO2 nanostructured hybrids was increased by two times when compared with that of its single component. Studies on the SPS revealed that the efficient light-induced charge separation and transfer between MTPD and TiO2 was responsible for the improved photosensitivity. The MTPD/TiO2 hybrids exhibited high photosensitivity to ultraviolet light with weak intensity and acceptable stability under ultraviolet radiation, which endow the hybrids potential applications in the field of ultraviolet photodetection. [ABSTRACT FROM AUTHOR]

The effect of optical feedback noise of a laser diode on the stability of gas-absorption spectra was investigated by monitoring the optical absorption of CO2 gas. Lasing longitudinal mode instability greatly degraded the shape of the absorption spectra, and coherence collapse in the laser diode greatly broadened the spectra. The correlation between the optical feedback noise of the laser diode and the shape of the gas-absorption spectra was clarified on the basis of these spectral behaviors. [ABSTRACT FROM AUTHOR]

Abstract: Optical absorption spectra of Cu2+ d–d transition peak in sodium borosilicate glasses and their melts were measured from room temperature to 1100K. In the case of borate glass free from silicon, increase of the temperature above T g shifts the peak position to the low energy side and decreases the peak height. Peak width is gradually increased with the increase in temperature. On the other hand, in the case of silicate glass free from boron, peak width is decreased with the increase in temperature from room temperature to liquidus temperature. In addition, peak height is slightly decreased with the temperature increase in this temperature range. Further increase of the temperature makes the peak width large. In borosilicate glasses, temperature dependence of the optical absorption spectra is different both from borate and from silicate, and the temperature dependences of the peak position and of the peak height are very small. Temperature dependence of the peak width depends on the boron/silicon ratio. [Copyright &y& Elsevier]

We present the results of time-dependent density functional theory calculations of the optical absorption spectra of synthetic nucleobases and of their hydrogen-bonded and stacked base pairs. We focus on size-expanded analogues of the natural nucleobases obtained through the insertion of a benzene ring bonded to the planar heterocycles (x-bases), according to the protocol designed and realized by the group of Eric Kool (e.g., see:  Gao, J.; Liu, H.; Kool, E.T. Angew. Chem., Int. Ed.2005, 44, 3118, and references therein). We find that the modifications of the frontier electron orbitals with respect to natural bases, which are induced by the presence of the aromatic ring, also affect the optical response. In particular, the absorption onset is pinned by the benzene component of the HOMO of each x-base (xA, xG, xT, xC). In addition, the main trait of the H-bonding interbase coupling is a conspicuous red shift of spectral peaks in the low-energy range. Finally, the hypochromicity, a well-known fingerprint of stacking, is more pronounced in stacked xG−C and xA−T pairs than that in stacked G−C and A−T pairs, an index of enhanced stacking. [ABSTRACT FROM AUTHOR]

Abstract: The transient photocapacitance spectroscopy (TPC) was applied to measure the optical absorption spectra of hydrogenated amorphous silicon (a-Si:H) in metal-insulator–semiconductor (MIS) structure. The measured spectra show the features of optical transitions from both D0 and D− defect bands to conduction band. The stability of measurement was checked against the change of probe frequency. The availability of TPC in detecting the defect density changes was also tested by checking the well-known defect density increase in a-Si:H after light illumination. [Copyright &y& Elsevier]

A direct quantum-mechanical calculation of the intensity distribution in the two-photon absorption spectrum of benzonitrile is performed taking into account the Herzberg-Teller effect. The excitation mechanism of all the observed lines, including lines corresponding to the excitation of single-quantum nontotally symmetric vibrations and their combinations with totally symmetric modes, is analyzed. The results of the calculation, performed taking into account the frequency effect and the Duschinsky effect, agree satisfactorily with experimental data. This indicates that it is worthwhile to apply the quantum-mechanical method in calculations of the intensity distribution in the two-photon absorption spectra of cyclic molecules. [ABSTRACT FROM AUTHOR]

Abstract: The spin transition of the [Co(terpy)2]2+ complex (terpy=2,2′:6′,2″-terpyridine) is analysed based on experimental data from optical spectroscopy and magnetic susceptibility measurements. The single crystal absorption spectrum of [Co(terpy)2](ClO4)2 shows an asymmetric absorption band at 14400cm−1 with an intensity typical for a spin-allowed d–d transition and a temperature behaviour typical for a thermal spin transition. The single crystal absorption spectra of suggest that in this compound, the complex is essentially in the high-spin state at all temperatures. However, the increase in intensity observed in the region of the low-spin MLCT transition with increasing temperature implies an unusual partial thermal population of the low-spin state of up to about 10% at room temperature. Finally, high-spin→low-spin relaxation curves following pulsed laser excitation for [Co(terpy)2](ClO4)2 dispersed in KBr discs, and as a comparison for the closely related [Co(4-terpyridone)2](ClO4)2 spin-crossover compound are given. [Copyright &y& Elsevier]

Abstract: A polyalkylated triamine, 2,2′,4,4′-tetrabromo-4″-methyl-5,5′-bis(di(3,4-di-methylphenyl)amino)triphenylamine, was designed and successfully synthesized as a model precursor for purely organic cationic high-spin systems. Cyclic voltammetry measurement revealed that the triamine gives stable mono- and dicationic states and fairly unstable tricationic state. Novel electron transfer stopped-flow (ETSF) methods were invoked for characterizing the absorption spectra of the corresponding mono- and oligo-cationic states. The triplet state of the dication was confirmed by ESR spectroscopy. [Copyright &y& Elsevier]