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The model Hamiltonian approach of Köppel et al. [Adv. Chem. Phys. 57, 59 (1984)] is used to analyze the electronic spectroscopy of the nitrate radical (NO3). Simulations of negative ion photodetachment of NO3-, the X 2A2′←B 2E′ dispersed fluorescence spectrum of NO3, and the B 2E′←X 2A2′ absorption spectrum are all in qualitative agreement with experiment, indicating that the model Hamiltonian contains most or all of the essential physics that govern the strongly coupled X 2A2′ and B 2E′ electronic states of the radical. All 14 bands seen in the dispersed fluorescence spectrum below 2600 cm-1 are assigned based on the simulations, filling in a few gaps left by previous work, and 7 additional bands below 4000 cm-1 are tentatively assigned. The assignment is predicated on the assumption that the ν3 level of NO3 is near 1000 cm-1 rather than 1492 cm-1 as is presently believed. Support for this reassignment (which associates the 1492 cm-1 band with the ν1+ν4 level) comes from both the model Hamiltonian spectrum and a Fourier-transform infrared feature at 2585 cm-1 that is consistent with the large and positive cross anharmonicity between ν1 and ν4 needed for the alternative 1492 cm-1 assignment. An apparent systematic deficiency exists in the treatment of the model Hamiltonian for levels involving ν4. A discussion of the correlation between energy levels in the rigid D3h and C2v limits is illustrative, and provides insight into just how hard it is to treat the degenerate bending coordinate (q4) of NO3 accurately. [ABSTRACT FROM AUTHOR]

The entire ultraviolet-visible absorption spectrum of benzophenone in water is studied and compared with the same spectrum in gas phase. Five transitions are considered, and the corresponding solvatochromic shifts are obtained and compared to experiment. Using a sequential procedure of Monte Carlo simulations and quantum mechanical calculations, liquid configurations were generated and an averaged spectrum of the solution was calculated. The solute polarization was included by an iterative procedure where the atomic charges of the solute were obtained as an average with the solvent distribution. The calculated average dipole moment of benzophenone in water, with MP2/6-31++G(d,p), converges to the value of 5.84±0.05 D, 88% larger than the gas-phase value of 3.11 D. Using 100 statistically uncorrelated configurations and solvation shells with 235 explicit water molecules selected by a minimum-distance distribution of solvent shells, instead of the usual radial distribution, the excitation energies were obtained from solute-solvent all-valence-electron INDO/CIS calculations. The shift of the weak n-π* transition is obtained as 2045±40 cm-1 and the strong and broad π-π* shift as -1790±30 cm-1. These results are in good agreement with the experimental values of 2200 and -1600 cm-1, respectively. Standard procedure used by common force fields to generate atomic charges to describe the electrostatic moments of the solute, with HF/6-31G(d), gives a dipole moment of 3.64 D. Using these standard charges in the simulation, the average shifts are calculated as 1395±35 and -1220±25 cm-1, both about 600 cm-1 smaller in magnitude than those obtained with the average converged fully polarized solute. The influence of the solute polarization in the solute-solvent interaction and, in particular, in solute-solvent hydrogen bonds is analyzed. [ABSTRACT FROM AUTHOR]

Mixed quantum-classical statistical mechanics is employed to calculate dipole moment correlation function and linear absorption spectra. A quantum two-level subsystem interacting with quantum vibrations (primary oscillators) which in turn are coupled to a classical bath composed of infinite set of harmonic oscillators is used as a dissipative system. Starting with mixed quantum-classical Liouville equation for the evaluation of the mixed quantum-classical dipole moment correlation function and using coherent states and the inverse of Baker-Campbell-Hausdorf formula to evaluate the trace over the primary oscillators, whereby, a closed analytical expression for the electronic dipole moment correlation function is obtained. Illustrations of several absorption spectra at different temperatures are provided. An approximate optical four-point correlation is obtained in the high temperature limit. A strategy for deriving an exact optical four-point correlation is suggested. [ABSTRACT FROM AUTHOR]

The UV/visible spectra of a series of indigo derivatives have been evaluated by using ab initio methods. The combination of the Polarizable continuum model for estimating bulk solvent effects with the TD-B3LYP/6-311+G(2d,p)//B3LYP/6-311G(d,p) level of approximation, leads to an accurate description of the wavelength of maximum absorption of indigoïds compounds. Using this procedure, we have assessed the effects of both the surroundings (solvent and solid state) and the substitution pattern. For the latter, we obtained a mean absolute deviation of only 7 nm (0.02 eV) compared to experiment, for a set of 86 molecules/solvents. [ABSTRACT FROM AUTHOR]

We have investigated theoretically the interband excitonic absorption spectra and the coupling behaviors of coupled symmetric triple Zn1-xCdxSe/ZnSe quantum wells with diluted Mn doping in the central well under external magnetic field. The results show that the magnetic field can effectively adjust the energy levels and the optical properties of the coupled multiple quantum wells (CMQWs). The coupling behaviors of the CMQWs are very sensitive to the central well depth. The effect of the magnetic-field-introduced parabolic-confined potential on the main features of the absorption spectra can be neglected at moderate magnetic-field densities. [ABSTRACT FROM AUTHOR]

We consider three distinct methods of calculating the vibronic levels and absorption spectra of molecular dimers coupled by dipole-dipole interactions. The first method is direct diagonalization of the vibronic Hamiltonian in a basis of monomer eigenstates. The second method is to use creation and annihilation operators leading in harmonic approximation to the Jaynes–Cummings Hamiltonian. The adiabatic approximation to this problem provides insight into spectral behavior in the weak and strong coupling limits. The third method, which serves as a check on the accuracy of the previous methods, is a numerically exact solution of the time-dependent Schrödinger equation. Using these methods, dimer spectra are calculated for three separate dye molecules and show good agreement with measured spectra. [ABSTRACT FROM AUTHOR]

A general formulation of nonperturbative quantum dynamics of solutes in a condensed phase is proposed to calculate linear and nonlinear vibrational line shapes. In the weak solute-solvent interaction limit, the temporal absorption profile can be approximately factorized into the population relaxation profile from the off-diagonal coupling and the pure-dephasing profile from the diagonal coupling. The strength of dissipation and the anharmonicity-induced dephasing rate are derived in Appendix A. The vibrational energy relaxation (VER) rate is negligible for slow solvent fluctuations, yet it does not justify the Markovian treatment of off-diagonal contributions to vibrational line shapes. Non-Markovian VER effects are manifested as asymmetric envelops in the temporal absorption profile, or equivalently as side bands in the frequency domain absorption spectrum. The side bands are solvent-induced multiple-photon effects which are absent in the Markovian VER treatment. Exact path integral calculations yield non-Lorentzian central peaks in absorption spectrum resulting from couplings between population relaxations of different vibrational states. These predictions cannot be reproduced by the perturbative or the Markovian approximations. For anharmonic potentials, the absorption spectrum shows asymmetric central peaks and the asymmetry increases with anharmonicity. At large anharmonicities, all the approximation schemes break down and a full nonperturbative path integral calculation that explicitly accounts for the exact VER effects is needed. A numerical analysis of the O–H stretch of HOD in D2O solvent reveals that the non-Markovian VER effects generate a small recurrence of the echo peak shift around 200 fs, which cannot be reproduced with a Markovian VER rate. In general, the nonperturbative and non-Markovian VER contributions have a stronger effect on nonlinear vibrational line shapes than on linear absorption.© 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Irradiance dependence of excitonic nonlinear absorption in cadmium sulfide (CdS) nanocrystals has been studied by using Z-scan method with nanosecond laser pulses. The wavelength dependence of nonlinear absorption has also been measured near the excitonic transition of 1S(e)–1S3/2(h). We observe the saturable absorption, which can be described by a third-order and a fifth-order nonlinear process for both 3.0-nm-sized and 2.3-nm-sized CdS nanocrystals. The experimental results show that the excitonic nonlinear absorption of CdS nanocrystals is greatly enhanced with decreasing particle size. A two-level model is utilized to explain both irradiance and wavelength dependence of the excitonic nonlinearity. © 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]

We show that the absorption spectra of single-layer GaSe and GaTe in the hexagonal phase feature exciton peaks with distinct polarization selectivity. We investigate these distinct features from first-principles calculations using the GW-BSE formalism. We show that, because of the symmetry of the bands under in-plane mirror symmetry, the bound exciton states selectively couple to either in-plane or out-of-plane polarization of the light. In particular, for a p-polarized light absorption experiment, the absorption peaks of the hydrogenic s-like excitons emerge at large angle of incidence, while the overall absorbance reduces over the rest of the spectrum. [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]

Quantum dynamical and electronic structure calculations are combined to investigate the mechanism of exciton migration in an oligothiophene HJ aggregate, i.e., a combination of oligomer chains (J-type aggregates) and stacked aggregates of such chains (H-type aggregates). To this end, a Frenkel exciton model is parametrized by a recently introduced procedure [Binder et al., J. Chem. Phys. 141 , 014101 (2014)] which uses oligomer excited-state calculations to perform an exact, point-wise mapping of coupled potential energy surfaces to an effective Frenkel model. Based upon this parametrization, the Multi-Layer Multi-Configuration Time-Dependent Hartree (ML-MCTDH) method is employed to investigate ultrafast dynamics of exciton transfer in a small, asymmetric HJ aggregate model composed of 30 sites and 30 active modes. For a partially delocalized initial condition, it is shown that a torsional defect confines the trapped initial exciton, and planarization induces an ultrafast resonant transition between an HJ-aggregated segment and a covalently bound “dangling chain” end. This model is a minimal realization of experimentally investigated mixed systems exhibiting ultrafast exciton transfer between aggregated, highly planarized chains and neighboring disordered segments. [ABSTRACT FROM AUTHOR]

A major obstacle for computing optical spectra of solids is the lack of reliable approximations for capturing excitonic effects within time-dependent density functional theory. We show that the accurate prediction of strongly bound electron-hole pairs within this framework using simple approximations is still a challenge and that available promising results have to be revisited. Deriving a set of analytical formulas we analyze and explain the difficulties. We deduce an alternative approximation from an iterative scheme guided by previously available knowledge, significantly improving the description of exciton binding energies. Finally, we show how one can "read" exciton binding energies from spectra determined in the random phase approximation, without any further calculation. [ABSTRACT FROM AUTHOR]

We study quasi-one-dimensional electron-hole (e-h) systems by applying a self-consistent screened T-matrix approximation (SSTA), which can treat an e-h pair embedded in the background of the exciton-plasma mixture, characterized by the exciton ionization ratio. Two classical-quantum crossovers are found. The first crossover takes place as the drastic suppression of ionization ratio, representing the onset of the quantum dissociation of the exciton (binding-energy reduction and level-broadening effects). The second one can be seen in a gradual change in the interband absorption-gain and photoluminescence spectra: Moss-Burstein effects become significant, and the e-h plasma starts to dominate the optical gain. Most of the features of the absorption-gain spectra observed in the recent experiments can be captured semiquantitatively by our SSTA. [ABSTRACT FROM AUTHOR]

Particular features and quenching mechanisms of exciton luminescence of water-soluble nanocomposites that are formed as a result of the interaction of surface charged semiconductor quantum dots (QDs) CdSe/ZnS ( d = 2.8 nm) and cationic porphyrins (HTMPyrP and ZnTMPyrP) have been studied theoretically and experimentally. It has been found that, in CdSe/ZnS⊕Porphyrin conjugates, there occurs long-range inductive resonance electronic excitation energy transfer from surface modified (with thioglycolic or mercaptoundecanoic acid) QDs to porphyrins, which is accompanied by quenching of the exciton luminescence of QDs and an increase in the fluorescence intensity of porphyrin. It has been shown that, when mercaptoundecanoic acid is used as a QD shell, the QD luminescence quenching efficiency by porphyrins follows the Förster-Galanin theory and depends on the overlap integral between the CdSe/ZnS luminescence band and the absorption spectra of free-base porphyrin HTMPyrP and its metal complex ZnTMPyrP. It has been revealed that, as the QDs ↔ Zn-porphyrin intercenter distance decreases from 39.1 (mercaptoundecanoic acid) to 30.1), a considerable QD luminescence quenching is observed; however, the energy transfer efficiency substantially decreases, from 55% in the former case to 23% in the latter one. Based on the spectral-luminescent data and quantum-chemical calculations, it has been found that the chemical change of HTMPyrP in the structure of the complex with CdSe/ZnS QDs passivated by thioglycolic or mercaptoundecanoic acid is caused by the formation of a metal complex ZnTMPyrP. Based on calculations of the redox-potentials, it has been concluded that the low luminescence quantum yield of CdSe/ZnS QDs passivated by residues of mercaptocarboxylic acids S(CH)COO and its dependence on the number of CH groups are related to the possibility of photoinduced electron transfer from the HOMO of passivating molecules to QDs (QD* ⇐ S(CH) nCOO hole transfer). It has been shown that the quenching of the exciton luminescence of QDs in heterogeneous structures CdSe/ZnS(thioglycolic acid)⊕ZnTMPyrP, which is complementary to the energy transfer, can be caused by the photoinduced electron transfer that involves the participation of the LUMO of the ZnTMPyrP molecule (QD* ⇒ ZnTMPyrP). [ABSTRACT FROM AUTHOR]

Unsaturated absorption coefficients in pure carbon dioxide at pressures of 1 and 100 Torr and in CO-N and CO-He binary mixtures at a pressure of 100 Torr have been measured in the temperature range of 296-700 K using a frequency-stabilized tunable CO laser. The collisional self-broadening coefficient, the relative coefficients of collisional broadening caused by N and He buffer gases, and their temperature dependences have been determined for the R22 absorption line of the 100-001 transition in CO molecules. [ABSTRACT FROM AUTHOR]

We introduce a model comprehensively describing the optical features of amorphous silicon dioxide (a-SiO2) in the spectral range from ~8 up to ~11 eV. Our model is grounded on the critical analysis of the temperature dependence of Kramers-Kronig-derived absorption spectra in the range from ~8 up to ~17.5 eV, together with the features of the Urbach absorption tail and of self-trapped exciton emission. In a paper we recently published [ Phys. Rev. Lett. 105 116401 (2010) ] we showed the 10.4-eV resonance in the absorption spectra to feature a close Lorentzian line shape, thus implying a delocalized nature for excitons in a-SiO2. Here we provide estimations of the main parameters ruling exciton dynamics in SiO2, such as the energy of the mean lattice vibrational mode coupled to excitons (ħω0=0.083 eV), the half width of the excitonic energy band (B~2 eV), the root-mean-square amplitude of site-to-site energy fluctuations of exciton energy (D~0.7 eV), and the exciton-phonon coupling constant (g~2.1). The quantum yield of excitonic emission (η~10-3) at T=10 K in a-SiO2 is determined as well. Our model suggests that a-SiO2 features an indirect gap near ~9 eV and a direct one near ~11 eV, and allows a coherent description of the properties of the intrinsic Urbach absorption tail. The latter results are satisfactorily explained as arising from the momentary self-trapping of the 10.4-eV exciton. As far as near-edge absorption properties are concerned, our model places SiO2 in the wider context of wide-band-gap solids, such as LiF or NaF, where excitons are weakly scattered, but strongly coupled to phonons. On the whole, the present study shows that exciton dynamics accounts for all optical properties of a-SiO2 from ~8 up to ~11 eV. [ABSTRACT FROM AUTHOR]

Absorption spectra of small molecular aggregates (oligomers) are considered. The dipole-dipole interaction between the monomers leads to shifts of the oligomer spectra with respect to the monomer absorption. The line-shapes of monomer as well as oligomer absorption depend strongly on the coupling to vibrational modes. Using a recently developed approach [Roden et al., PRL 103, 058301] we investigate the length dependence of spectra of one-dimensional aggregates for various values of the interaction strength between the monomers. It is demonstrated, that the present approach is well suited to describe the occurrence of the J- and H-bands. [ABSTRACT FROM AUTHOR]

Optical spectroscopy and nanosecond flash photolysis (Nd:YAG laser, 355 nm, pulse duration 5 ns, mean energy 5 mJ/pulse) were used to study the photochemistry of Fe III(C 2O 4) 33−complex in aqueous solutions. The main photochemical process was found to be intramolecular electron transfer from the ligand to Fe(III) ion with formation of a primary radical complex [(C 2O 4) 2Fe II(C 2O 4•)] 3−. The yield of radical species (i.e., CO 2• −and C 2O 4• −) was found to be less than 6% of Fe III(C 2O 4) 33−disappeared after flash. [(C 2O 4) 2Fe II(C 2O 4•)] 3−dissociates reversibly into oxalate ion and a secondary radical complex, [(C 2O 4)Fe II(C 2O 4•)] −. The latter reacts with the initial complex and dissociates to Fe II(C 2O 4) and oxalate radical. In this framework, the absorption spectra and rate constants of the reactions of all intermediates were determined. [ABSTRACT FROM AUTHOR]

Abstract: A novel bimetallic 4f–3d complex [Er(C6H5NO2)3(H2O)2] n (1.5nZnCl4)·(2nH2O) (1) has been synthesized via hydrothermal reaction and structurally characterized by single-crystal X-ray diffraction. Complex 1 is characteristic of a novel one-dimensional polycationic chain-like structure. Photoluminescent investigation reveals that the title complex displays interesting emissions in green and red regions. The luminescence spectra show that the green emission is stronger than the red emission. The green and red emission bands are attributed to the characteristic emissions of 4F7/2, 2H11/2, 4S3/2, 4F9/2 → 4I15/2 of Er3+ ions. Optical absorption spectra of 1 reveal the presence of an optical gap of 3.85eV. [Copyright &y& Elsevier]

We present a comprehensive study of spectral photoluminescence (PL), photoconductivity and Hall mobility in undoped, n and p-type modulation-doped quantum wells of Ga1- x In x N y As1- y /GaAs with varying nitrogen concentration. We show that the increasing nitrogen composition red shifts the energy gap and this red shift is accompanied with a reduction of the 2D electron mobility in the quantum wells. True temperature dependence of the band gap, free from errors associated with nitrogen induced exciton trapping effects, is observed because in the modulation doped QW samples PL emission is dominated by band-to-band recombination and the S-shape temperature dependence is eliminated. Excellent fit to semi-experimental Varshni equation is obtained and the temperature dependence of the band gap in the linear regime (d E/d T) is tabulated as a function of nitrogen concentration and the type of dopant. [ABSTRACT FROM AUTHOR]

Polarization-dependent linear absorption, second-harmonic generation (SHG) and 3rd-order nonlinearities of well-aligned ZnO nanorod arrays have been investigated with ps pulses. The depressed spectral width and the enhanced intensity of reflective SHG along the long axis of ZnO nanorods were observed by using p-polarized pulses, which is explained by the optical confinements. The nonlinear absorption coefficient measured with s-polarization reached the maximum 4.0 × 104cm/GW at the wavelength [?]750 nm, which revealed a large two-photon resonance absorption attributed to the quantum confined exciton when the polarization is vertical to the long axis of ZnO nanorod. [ABSTRACT FROM AUTHOR]

A study is made of the excitonic absorption spectra of solid solutions of the system (KI)2–(1-x)AgI–xCuI. On the basis of the dependence of the parameters of the excitonic bands on the concentration x, it is established that solid solutions of the type K2Ag1-xCuxI3 are formed in the range 0≤x≤0.2. Substitution of Ag atoms by Cu atoms in the AgI42- tetrahedra, which form chains in the orthorhombic crystal K2AgI3, promotes the formation of quasi-1D exciton bands and spectra of the persistence type, according to the Onodera–Toyozawa classification, with a splitting off of the impurity band from the exciton band. Comparison with the results of studies of the excitonic spectra in solid solutions Rb2Ag1-xCuxI3 and Cs2Ag1-xCuxI3 attests to the appearance of the Rashba effect at small x and to qualitative agreement with the Onodera–Toyozawa theory. [ABSTRACT FROM AUTHOR]

Abstract: A Λ-type three-level atomic system in the electromagnetically induced transparency (EIT) configuration interacting with a broadband squeezed vacuum (SV) bath is studied with quantum interference (QI) between decay channels taken into account. We formulate two sufficient critical conditions for the medium to be dispersionless or absorptionless. Computational results for the dispersion and absorption spectra show that presence of both QI and SV offers more avenues to manipulate the group velocity of probe pulse for its variation from sub-luminal to super-luminal regimes. The relative phase between the two external fields is found to act as a control knob of the atomic medium. [Copyright &y& Elsevier]

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]

Lead iodide nanoparticles are synthesized in reverse micelle solution of AOT/H2O/n-heptane. Optical absorption spectra and TEM analysis indicated the formation of crystalline particles with an average radius of 1.5 nm, which is less than the Bohr radius of the exciton (1.9 nm) in bulk PbI2. Using theoretical models and optical spectra of quantum confined PbI2 nanoparticles, a radius of 1.5 nm and a thickness of 1.7 nm was calculated, which are in full agreement with the TEM results. Particles were isolated from the dispersed medium and were analysed by powder XRD and Raman spectroscopy, indicating the formation of a predominantly 2H-PbI2 polytype. This work presents the first case of fully isolated, fully characterized solid nanoparticles of PbI2. It also presents XRD and Raman spectrum for the first time for PbI2 nanoparticles of intermediate quantum confinement. [ABSTRACT FROM AUTHOR]

New absorption bands due to spin-forbidden transitions from the ground state to excited triplet states are found at 295 K in the near-IR absorption spectra of a number of Cu(II) complexes of octaethylporphyrin (OEP) that differ in the nature, number, and position of their side substituents. The frequency distribution, number, and nature of these transitions are analyzed using computer decomposition of complex contours into Gaussian components and additional data from the phosphorescence and phosphorescence excitation spectra (295–77 K). The d-π exchange integrals, determining the energy splitting ΔE = E(2T1) – E(4T1) in the compounds under study, are calculated on the basis of the experimental data obtained. It is shown that, in addition to the formally spin-allowed 2S0→2T1 transition (λmax = 833 nm), the absorption spectrum of the nonplanar CuOETPP molecule at 295 K exhibits the low-intensity spin-forbidden 2S0→4T1 transition (λmax = 937 nm). For this compound at 77 K, phosphorescence from the 4T1 state is observed (λmax = 955 nm), with a quantum yield equal to φPh = 0.0015 and a decay time amounting to τPh = 190 ns. For the CuOEP–Ph(o-NO2) molecule, which contains the electron-acceptor nitro group, direct absorption from the ground state S0 to a charge transfer (CT) state (λmax = 845 nm) is observed at 295 K. The extinction coefficient of this absorption and the energy of the CT state are determined. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

In the present work, results of investigations into the transient absorption of some organic compounds by the method of pulsed flash photolysis are given. Experimental investigations were carried out using an original setup of pulsed flash photolysis with an exciting pulse of XeCl-laser radiation of nanosecond duration and sensing by broadband laser-transient fluorescent radiation of a mixture of organic fluorophors called “white light” excited by the same source in the wavelength range 330–750 nm. The setup registers the short-living (singlet-singlet) and long-living (triplet-triplet) absorptions. The transient absorption spectra of already investigated para-terphenyl, naphthalene, and 1-phenyl-2(2-naphthyl)-ethylene molecules are presented; the spectra of the transient absorption and its nature are in good agreement with the experimental and calculated data published in the literature. We first investigated the transient absorption of LOC1 (S1-Sn at 580 nm and T1-Tn at 500 nm) and phenalemine 512 (S1-Sn at 395 nm). It is demonstrated that the experimentally observed induced absorption of phenalemine 512 and PD 789 is the S1-Sn absorption, which is in good agreement with the results of quantum-chemical calculations. [ABSTRACT FROM AUTHOR]

We report on very high efficiency deep-blue phosphorescent organic light-emitting devices (PHOLEDs) based on iridium(III) bis(4′,6′-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate (FIr6). Dual emissive layers consisting of an N,N′-dicarbazolyl-3,5-benzene layer doped with 4 wt % FIr6 and a p-bis(triphenylsilyly)benzene layer doped with 25 wt % FIr6 were employed to maximize exciton generation on FIr6 molecules. Combined with the p-i-n device structure, we achieved a low turn-on voltage of 3.2 V and very high power efficiencies of 25±2 lm/W at 100 cd/m2 and 20±2 lm/W at 1000 cd/m2 for such deep-blue PHOLEDs with peak emission at a wavelength of 458 nm. [ABSTRACT FROM AUTHOR]

The optical absorption spectra of single crystals of neodymium and samarium chromium borates are studied. A magnetic phase transition in NdCr3(BO3)4 (at T c = 8 ± 1 K) and SmCr3(BO3)4 (at T c = 5 ± 1 K) is observed. The effective magnetic field acting on the Nd3+ ion from the side of the ordered magnetic subsystem of chromium is estimated. [ABSTRACT FROM AUTHOR]

Singlet fission sensitized photovoltaics have the potential to surpass the Shockley-Queisser limit for a single-junction structure. We investigate the dynamics of triplet excitons resulting from singlet fission in pentacene and their ionization at a C60 heterojunction. We model the generation and diffusion of excitons to predict the spectral response. We find the triplet diffusion length in polycrystalline pentacene to be 40 nm. Poly(3-hexylthiophene) between the electrode and pentacene works both to confine triplet excitons and also to transfer photogenerated singlet excitons into pentacene with 30% efficiency. The lower bound for the singlet fission quantum efficiency in pentacene is 180 ± 15%. [ABSTRACT FROM AUTHOR]

We demonstrate alpha-particle detection in an n-type 4H-SiC Schottky diode detector up to a temperature of 500 °C using an Am-241 disc source. The measured spectra were used to calculate the electron-hole pair creation energy in 4H-SiC and its non-bandgap contribution, which are both found to decrease with increasing temperature. The full width at half maximum (FWHM) of the measured alpha-energy peaks was found to increase exponentially with temperature due to an exponential increase of leakage current. For our measurement system, above 300 °C, where the leakage current was 10-6 A, this increase exceeded the FWHM at room temperature. [ABSTRACT FROM AUTHOR]