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The Ã-X electronic absorption spectrum of vinoxy radical has been investigated using room temperature cavity ringdown spectroscopy. Analysis of the observed bands on the basis of computed vibrational frequencies and rotational envelopes reveals that two distinct types of features are present with comparable intensities. The first type corresponds to “normal” allowed electronic transitions to the origin and symmetric vibrations in the à state. The second type is interpreted in terms of excitations to asymmetric à state vibrations, which are only vibronically allowed by Herzberg–Teller coupling to the B state. Results of electronic structure calculations indicate that the magnitude of the Herzberg–Teller coupling is appropriate to produce vibronically induced transitions with intensities comparable to those of the normal bands. [ABSTRACT FROM AUTHOR]

The diagonal linewidth in two-dimensional infrared spectra is often narrower than the distribution of transition frequencies. The width along the antidiagonal is broader than predicted by the lifetime broadening. These effects arise from time-dependent fluctuations of the transition frequencies. They can be accounted for with a semiclassical approach. For systems with many coupled vibrational modes, this approach, however, becomes computationally too demanding to be practically applicable. A time-averaging approximation was suggested for linear infrared absorption spectra. In this paper, we demonstrate that the averaging can be optimized to fit a broader scale of frequency fluctuations by using a Gaussian weight function instead of the originally proposed box function. We further generalize the time-averaging method to allow the simulation of two-dimensional infrared spectra and demonstrate the method on a simple system. The approximation delivers a large speed-up of the calculation without losing significant accuracy. [ABSTRACT FROM AUTHOR]

The spectroscopic technique of threshold ion-pair production spectroscopy (TIPPS) has been applied to the triatomic molecule HCN. We have recorded the total ion-pair yield and TIPP spectra for the HCN→H++CN- process using coherent vacuum ultraviolet excitation. From the simulation of our high-resolution TIPP spectrum we have precisely measured the HCN ion-pair threshold EIP0 to be 122 244±4 cm-1. This value could be used to determine the bond dissociation energy D0(H-CN) to unprecedented accuracy. Our fitting result also showed that rotationally excited instead of cold CN- fragment is favored as the ion-pair dissociation product in the threshold region. [ABSTRACT FROM AUTHOR]

Recent theoretical studies on linear absorption spectra of dye-semiconductor systems [perylene attached to nanostructured TiO2, L. Wang et al., J. Phys. Chem. B 109, 9589 (2005)] are extended here in different respects. Since the systems show ultrafast photoinduced heterogeneous electron transfer the time-dependent formulation used to compute the absorbance is also applied to calculate the temporal evolution of the sub-100 fs charge injection dynamics after a 10 fs laser-pulse excitation. These studies complement our recent absorption spectra fit for two perylene bridge-anchor group TiO2 systems. Moreover, the time-dependent formulation of the absorbance is confronted with a frequency-domain description. The latter underlines the central importance of the self-energy caused by the coupling of the dye levels to the semiconductor band continuum. The used model is further applied to study the effect of different parameters such as (1) the dependence on the reorganization energies of the involved intramolecular transitions, (2) the effect of changing the transfer integral which couples the excited dye state with the band continuum, and (3) the effect of the concrete form of the semiconductor band density of states. Emphasis is also put on the case where the charge injection level of the dye is near or somewhat below the band edge. This nicely demonstrates the change from a structureless absorption to a well-resolved vibrational progression including characteristic shifts of the absorption lines which are a direct measure for the dye-semiconductor coupling. [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]

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]

Infrared absorption spectroscopy of few hundred H3+ ions trapped in a 22-pole ion trap is presented using chemical probing as a sensitive detection technique down to the single ion level. By exciting selected overtone transitions of the (v1=0,v2l=31)←(0,00) vibrational band using an external cavity diode laser an accurate diagnostics measurement of the effective translational and rotational temperatures of the trapped ions was performed. The absolute accuracy of the measured transition frequencies was improved by a factor of four compared to previous plasma spectroscopy measurements using velocity modulation [Ventrudo et al., J. Chem. Phys. 100, 6263 (1994)]. The observed buffer gas cooling conditions in the ion trap indicate how to cool trapped H3+ ions into the lowest ortho and para rotational states. Future experiments will utilize such an internally cold ion ensemble for state-selected dissociative recombination experiments at the heavy ion storage ring Test Storage Ring (TSR). © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The optical absorption spectra in a quantum well driven both by an intense terahertz (THz) and by an optical pulse are theoretically investigated within the theory of density matrix. We found that the optical absorption spectra and the splitting of the excitonic peaks splitting can be controlled by changing the THz field intensity and/or frequency. The Autler–Towns splitting is a result of the THz nonlinear dynamics of confined excitons, which is in agreement with the experiments. In addition, the dependence of the optical absorption on the quantum well width and the carrier density is also discussed. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A detailed photophysical picture is elaborated for a structurally well-defined and symmetrical bis-tetracene dimer in solution. The molecule was designed for interrogation of the initial photophysical steps (S1 → 1TT) in intramolecular singlet fission (SF). (Triisopropylsilyl)acetylene substituents on the dimer TIPS-BT1 as well as a monomer model TIPS-Tc enable a comparison of photophysical properties, including transient absorption dynamics, as solvent polarity is varied. In nonpolar toluene solutions, TIPS-BT1 decays via radiative and nonradiative pathways to the ground state with no evidence for dynamics related to the initial stages of SF. This contrasts with the behavior of the previously reported unsubstituted dimer BT1 and is likely a consequence of energetic perturbations to the singlet excited-state manifold of TIPS-BT1 by the (trialkylsilyl)acetylene substituents. In polar benzonitrile, two key findings emerge. First, photoexcited TIPS-BT1 shows a bifurcation into both arm-localized (S1-loc) and dimer-delocalized (S1-dim) singlet exciton states. The S1-loc decays to the ground state, and weak temperature dependence of its emissive signatures suggests that once it is formed, it is isolated from S1-dim. Emissive signatures of the S1-dim state, on the other hand, are strongly temperature-dependent, and transient absorption dynamics show that S1-dim equilibrates with an intramolecular charge-transfer state in 50 ps at room temperature. This equilibrium decays to the ground state with little evidence for formation of long-lived triplets nor 1TT. These detailed studies spectrally characterize many of the key states in intramolecular SF in this class of dimers but highlight the need to tune electronic coupling and energetics for the S1 → 1TT photoreaction. [ABSTRACT FROM AUTHOR]

YAlO[sub 3] single crystal doped with Ce[sup 3+] at concentration 1% was grown by the temperature gradient technique. The as-grown crystal was pink. After H[sub 2] annealing or air annealing at 1400 °C for 20 h, the crystal was turned into colorless. We concluded there were two kinds of color centers in the as-grown crystal. One is F[sup +] center attributed to absorption band peaking at about 530 nm, the other is O[sup -] center attributed to absorption band peaking at about 390 nm. This color centers model can be applied in explaining the experiment phenomena including the color changes, the absorption spectra changes, and the light yield changes of Ce:YAP crystals before and after annealing. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The absorption spectrum of KPbI thin films is studied in the spectral range 2-6 eV within the temperature interval 90-470 K. Localization of excitons in the sublattice of the compound containing lead ions is established. Excitons are shown to be of two-dimensional nature. [ABSTRACT FROM AUTHOR]

Abstract: The effects of transverse electric field on the energy levels of electron and heavy hole, exciton binding energy and excitonic absorption spectra of GaAs parabolic quantum wire are theoretically investigated in detail. The results indicate that the electron and hole energy levels, exciton binding energy, excitonic absorption coefficient and absorption energy becomes smaller with the increase of electric field. That is more significant at the condition of weaker parabolic confinement potential. The phenomena can be explained by the separation of overlap integral of the electron and hole at the ground states. [Copyright &y& Elsevier]

Abstract: An investigation of the influence of a laser field on the exciton absorption spectra and the refractive indexes has been performed by using the matrix diagonalization and the compact density-matrix methods. Electrons and holes are confined by the parabolic potential of the quantum dot. We conclude that in quantum dots the laser field amplitude provides an important effect on the linear, third-order nonlinear, and total optical absorption coefficients as well as the refractive index changes. [Copyright &y& Elsevier]

Electron photodetachment from the aromatic anion phenolate excited into the π--&pi* singlet excited state (S1) in aqueous solution is studied with ultrafast transient absorption spectroscopy with a time resolution of better than 50 fs. Broadband transient absorption spectra from 300 to 690 nm are recorded- The transient bands are assigned to the solvated electron, the phenoxyl radical, and the phenolate S1, excited state, and confirmation of these assignments is achieved using both KNO3 as electron quencher and time-resolved fluorescence to measure singlet excited state dynamics. The phenolate fluorescence lifetime is found to be short (∼20 ps) in water, but the fast decay is only in part due to the electron ejection channel from S1. Using global target analysis, two electron ejection channels are identified, and we propose that both vibrationally hot S1 state and the relaxed S1 state are direct precursors for the solvated electron. Therefore, electron ejection is found just to compete with picosecond time scale vibrational relaxation and electronic radiationless decay channels. This contrasts markedly with <100 fs electron detachment processes for inorganic anions. [ABSTRACT FROM AUTHOR]

The radiative recombination of triplet exciton, is studied here theoretically in inorganic amorphous and organic crystalline semiconductors. A new time-dependent exciton–spin–orbit–photon interaction operator derived recently is used to calculate rates of radiative recombination of triplet excitons and the corresponding radiative lifetimes. It is illustrated that the new operator gives rise to a first order non-zero term responsible for the triplet photoluminescence. Results agree quite well with the known experimental results. [ABSTRACT FROM AUTHOR]

We have made a detailed study of the extended X-ray absorption fine spectra (EXAFS) at the K edge of aqueous Y ion and at L3 edges of aqueous lanthanide ions and thereby elucidated the systematic changes in their hydration structures. Anomalous peaks arising from double-electron excitation (2p, 4d → 5d, 5d) appear in the EXAFS signals of La3+-Tb3+ between 5-7 Å-1. We established a removal process of double-electron excitation from EXAFS spectra. Using that process, we confirmed that the intensity and energy position of the extracted double-electron excitation are comparable to previously reported data. The presence of double-electron excitation engenders a smaller error than the errors estimated in the fitting process. Consequently, double-electron excitation does not seriously affect the determination of the structures of REE3+ aquo ions in the first coordination sphere. Subsequent EXAFS analyses of hydrated REE3+ ions suggest that the hydration numbers, the interatomic distances, and the Debye-Waller factors decrease from 9.7, 2.55 Å, and 9.0 × 10-3 Å2 for La3+ to 7.9, 2.31 Å, and 5.7 × 10-3 Å2 for Lu3+. These parameters change as a sigmoid curve with increasing atomic number. The hydration structures of REE3+ ions are inferred to change from the nonahydrated structure for La3+-Nd3+ to the octahydrated structure for Tb3+-Lu3+ through intermediate structures for Sm3+, Eu3+, and Gd3+. In addition, the hydration state of Y3+ closely resembles that of Ho3+ because the two have almost identical ionic radii. [ABSTRACT FROM AUTHOR]

Hemopexin (Hx) functions as a major heme scavenging protein in blood plasma and as such circulates without heme bound. In recent work, we have demonstrated that Hx binds metal ions in vitro in a manner that varies from one metal ion to another and that changes with heme binding. The structural consequences of metal ion binding to the form of Hx that dominates in plasma have now been evaluated by monitoring metal ion-linked changes in tertiary structure of the protein as reflected by changes in the near-UV CD spectrum and the ultraviolet absorption spectrum as a function of temperature. As part of this analysis we have developed thermally induced difference absorption maps (TIDAMs) to afford efficient visualization of temperature-dependent changes in the UV spectrum of Hx that are induced by binding of metal ions. The results are interpreted in terms of recent models proposed for metal ion binding sites on Hx and have implications for the possible modulation of heme binding to Hx by metal ions in vivo. [ABSTRACT FROM AUTHOR]

Asymmetric double quantum wells (ADQWs) are optimized to exhibit maximum optical modulation sensitivity by varying the barrier width, barrier position, and well width. Anticrossing of the two lowest excitons in ADQWs significantly enhances the modulation sensitivity. Consideration of exciton mixing is crucial to obtain accurate estimates of the effects. For a given linewidth of the excitonic peaks, we find optimum structural parameters that exhibit maximum modulation sensitivity. Values of dα/dE of ∼ 6.51 × 104 kV-1 at 4.2 K and of ∼ 1.25 × 10³ kV-1 at 298 K are predicted in GaAs-based ADQWs. The result provides new design guidelines in fabricating high-sensitivity QW electroabsorption modulators. [ABSTRACT FROM AUTHOR]

Black dye (BD), isomer 1 ([RuII(H3-tctpy)(NCS)3]-1, where H3-tctpy = 4,4′,4″-tricarboxy-2,2′:6,2″-terpyridine) is known to be an excellent sensitizer for dye-sensitized solar cells and exhibits a very good near-IR photo response, compared to other ruthenium dyes. Because isothiocyanate is a linear ambidentate ligand, BD has three other linkage isomers, [Ru(H3-tctpy)(NCS)2(SCN)]-1, isomer 2 and 2′, and [Ru(H3-tctpy))(SCN)3]-1, isomer 3. In this study, we have calculated the geometry of BD and its isomers by DFT. Further, we have analyzed the bonding in these isomers using NBO methods. TDDFT calculations combined with scalar relativistic zero-order regular approximations (SR-ZORA) have been carried out to simulate the absorption spectra. Calculations have been performed for the isomers both in vacuo and in solvent (ethanol). The inclusion of the solvent is found to be important to obtain spectra in good agreement with the experiment. The first absorption bands are dominated by the metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT). [ABSTRACT FROM AUTHOR]

Low-temperature emission and polarized absorption spectra have been recorded for U3+ ions diluted in Cs3Lu2Cl9 and Cs3Y2I9 host crystals. The experimental crystal-field levels were fitted to 13 parameters of a semiempirical Hamiltonian representing the combined atomic, one-electron crystal field (CF) as well as two-particle correlation crystal-field (CCF) operators. The red shift of the first f−d transitions from ~14 800 cm-1 in the spectrum of U3+:Cs3Lu2Cl9 to as low as 11 790 cm-1 in that of U3+:Cs3Y2I9 has been attributed to an increase in the covalence of the U3+−X- bonds. Comparison of the differences in the Coulomb repulsion strength between U3+ and Er3+ ions in Cs3Lu2Cl9 and Cs3Y2I9 crystals suggests that the 5f electrons of U3+ ions are more 3d-like than 4f. The CF splitting of the 2H9/2 and 4F5/2 multiplets is unexpectedly larger for U3+:Cs3Y2I9 than for U3+:Cs3Lu2Cl9, which may be viewed as a result of the proximity of f−d states. For a correct description of the energy level structure of the 2H9/2 and 4F5/2 multiplets, the inclusion of CCF terms in the parametric Hamiltonian has proved to be essential. The larger f−f transition intensities for U3+:Cs3Y2I9 were also considered to be a consequence of the red shift of the first f−d states. The inadequacy in determination of the minor atomic parameters (other than parameters for Coulomb and spin−orbit interactions) and the insufficient inclusion of the influence of excited configuration in the applied CF Hamiltonian are assumed to be the main deficiencies preventing a better agreement between the experimental and calculated energies of CF levels. [ABSTRACT FROM AUTHOR]

Abstract: A new technique of expressing slight differences in metal ion concentrations by clear difference in colour was established for visual threshold detection of trace metal ions. The proposed method is based on rapid change of the mole fraction of the homo–binuclear complex (M2L) about a ligand in a narrow range of the total metal ion concentration (MT) in a small excess, in case the second metal ion is bound to the reagent molecule which can bind two metal ions. Theoretical simulations showed that the highly sensitive colour change within slight differences in metal ion concentrations would be realized under the following conditions: (i) both of the stepwise formation constants of complex species are sufficiently large; (ii) the stepwise formation constant of the 1:1 complex (ML) is larger than that of M2L; and (iii) the absorption spectrum of M2L is far apart from the other species in the visible region. Furthermore, the boundary of the colour region in MT would be readily controlled by the total ligand concentration (LT). Based on this theory, the proposed model was verified with the 3,3′-bis[bis(carboxymethyl)amino]methyl derivatives of sulphonephthalein dyes such as xylenol orange (XO), methylthymol blue (MTB), and methylxylenol blue (MXB), which can bind two metal ions at both ends of a π-electron conjugated system. The above-mentioned model was proved with the iron(III)–XO system at pH 2. In addition, MTB and MXB were suitable reagents for the visual threshold detection of trivalent metal ions such as iron(III), aluminium(III), gallium(III) and indium(III) ion in slightly acidic media. The proposed method has been applied successfully as a screening test for aluminium(III) ion in river water sampled at the downstream area of an old mine. [Copyright &y& Elsevier]

We present the basic steps for the study of the linear near field absorption spectra of semiconductor quantum dots under magnetic field of variable orientation. We show that the application of the magnetic field alone is sufficient to induce -increasing the spot illuminated by the near field probe- interesting features to the absorption spectra. [ABSTRACT FROM AUTHOR]

A mixed quantum classical molecular dynamics (QCMD) simulation of the silver and sodium cations in presence of an excess electron is reported. The silver cation is shown to be reduced by the hydrated electron and to form a stable, highly polarized, neutral atom. On the contrary, the sodium cation is not reduced and a metastable contact ion pair is observed. The resulting absorption spectra of both species are compared with experiments and shown to be in good agreement. Furthermore, the free energy curve for the charge separation was calculated and rationalized in terms of a thermodynamic cycle. Finally, a direct, reactive, molecular dynamics trajectory provides some useful informations on the reduction mechanism. [ABSTRACT FROM AUTHOR]

The principal types of electronic transitions in absorption spectra of deoxyvasicinone and its 6-amino- and 6-nitro-derivatives were determined by analyzing the electron-density distributions in excited states calculated using ZINDO/S. [ABSTRACT FROM AUTHOR]

We demonstrate that 3,4,9,10 perylenetetracarboxylic bisbenzimidazole (PTCBI) and 1,4,5,8-napthalene-tetracarboxylic-dianhydride (NTCDA) can function as electron conducting and exciton blocking layers when interposed between the acceptor layer and cathode. A low-resistance contact is provided by PTCBI, while NTCDA acts as an exciton blocking layer and optical spacer. Both materials serve as efficient electron conductors, leading to a fill factor as high as 0.70. By using an NTCDA/PTCBI compound blocking layer structure in a functionalized-squaraine/C60-based device, we obtain a spectrally corrected power conversion efficiency of 5.1±0.1% under 1 sun, AM 1.5G simulated solar illumination, an improvement of >25% compared to an analogous device using a conventional bathocuproine layer that has previously been shown to conduct electrons via damage-induced midgap states. [ABSTRACT FROM AUTHOR]

Photoabsorption spectra are calculated for the magic number clusters, (CdSe)3 and (CdSe)6, using an all-electron mixed basis GW scheme with the excitonic effect incorporated by solving the Bethe-Salpeter equation (BSE). The GW+BSE calculation provided clear size dependence of the optical gap as expected, while magnitude of the gap is overestimated compared to available experimental one. The gap is found very similarly overestimated when using the local density approximation (LDA) within the density functional theory because accidental error cancellation occurs between the significantly underestimated LDA gap and the excitonic effect neglected therein. The excitonic states are described by superposition of many one-particle states that would not be properly described within a one-particle theory, as clearly visualized in the plot of the exciton wavefunctions. [ABSTRACT FROM AUTHOR]

In general, single GaAs quantum wells surrounded by AlxGa1-xAs cladding layers show only weak photoluminescence corresponding to exciton recombination. This is attributed to the poor quality of the AlGaAs in the lower cladding layer resulting in a degraded interface and poor GaAs in the quantum well. The situation gets worse when the thickness of the bottom AlGaAs layer is increased, the GaAs thickness is reduced, or the Al mole fraction is increased. Using a graded three-period superlattice ahead of the quantum well causes the intensity of the photoluminescence associated with exciton recombination to increase to more than 160 times that associated with the conventional structure. This exciton recombination peak is due to either very shallow bound or free-electron recombination and has a full width at half-maximum of only 2 meV. [ABSTRACT FROM AUTHOR]