Excited State Levels Research Articles

Optical absorption spectra and energy levels of Er3+ ions in KTaO3 crystals

The optical absorption spectra of erbium-doped potassium tantalate (KTaO3:Er) crystals have been studied. Absorption lines corresponding to the intraconfiguration f-f electron transitions from the 4I15/2 ground state to the levels of 4F9/2, 4S3/2,2H11/2, 4F7/2, 4F5/2(4F3/2), 2H9/2, and 4G11/2 excited states of Er3+ ions have been observed in a wavelength range of 350–660 nm. The transitions to 4F9/2, 2H11/2, 4F7/2, and 2H9/2 levels have been studied in detail at T = 2 K. Based on the obtained results, it is suggested that Er3+ impurity centers of two types exist in KTaO3:Er3+ crystals. The number of lines observed for the major type centers corresponds to that theoretically possible for Er3+ ions in a noncubic crystal field with a local compensation of the impurity charge. The energy positions of the levels of excited states for the observed transitions are determined.

The electronic spectrum of the fluoroborane free radical. I. Theoretical calculation of the vibronic energy levels of the ground and first excited electronic states

The fluoroborane (HBF) free radical has a large vibronic interaction which splits the orbitally degenerate (2)Pi state in the linear configuration into two separate electronic states, one strongly bent and one linear. The observed vibrational structure of the electronic transition between the Renner-Teller pair of states is very complex. As an aid to understanding the spectrum, the vibronic energy levels of the ground and first excited states have been calculated from high-level ab initio potential energy surfaces using a variational method. The vibrational frequencies and anharmonicities have been derived from these energy levels and the boron and hydrogen isotope shifts have been predicted. Although the ground state energy levels are for the most part well behaved, the excited state levels show substantial Renner-Teller mixing with nearby ground vibrational states. The calculations in the present work have been successfully used in the companion paper to make vibrational assignments of the laser-induced fluorescence spectra of HBF and DBF.

Electron affinity of lead: An ab initio four-component relativistic study

The electron affinity of lead is calculated to be 0.403 eV, using four-component relativistic multiconfigurational quasidegenerate perturbation theory. Uncontracted (27 s 23 p 16 d 10 f 2 g) Gaussian-type functions are used to generate valence basis functions (7 s 9 p − 10 p + 8 d ± 10 f ± 2 g ±) in the reduced frozen core approximation, where the KLM shells are frozen. The electrons in the remaining shells are correlated in the perturbation calculations with the (6 s, 6 p) complete active space. The calculated value is within 10% of the experimental value of 0.364 eV. The energy levels of the low-lying excited states of Pb and Pb − are also calculated.

Rhodaninedyes for dye-sensitized solar cells : spectroscopy, energy levels and photovoltaic performance

Three new sensitizers for photoelectrochemical solar cells were synthesized consisting of a triphenylamine donor, a rhodanine-3-acetic acid acceptor and a polyene connection. The conjugation length was systematically increased, which resulted in two effects: first, it led to a red-shift of the optical absorption of the dyes, resulting in an improved spectral overlap with the solar spectrum. Secondly, the oxidation potential decreased systematically. The excited state levels were, however, calculated to be nearly stationary. The experimental trends were in excellent agreement with density functional theory (DFT) computations. The photovoltaic performance of this set of dyes as sensitizers in mesoporous TiO2 solar cells was investigated using electrolytes containing the iodide/triiodide redox couple. The dye with the best absorption characteristics showed the poorest solar cell efficiency, due to losses by recombination of electrons in TiO2 with triiodide. Addition of 4-tert butylpyridine to the electrolyte led to a strongly reduced photocurrent for all dyes due to a reduced electron injection efficiency, caused by a 0.15 V negative shift of the TiO2 conduction band potential.

Up-conversion Luminescence of Terbium(III) in SiO2 and ZnO–SiO2 Glasses Induced by Simultaneous Absorption of Three Photons and Saturation

ABSTRACT Green up-conversion luminescence (UCL) of Tb3+ in SiO2 and ZnO–SiO2 glasses was observed with femtosecond (fs) laser (800 nm) excitation. The UCL mechanism of Tb3+ in both glasses contributed to the simultaneous three-photon absorption. The saturation effect of Tb3+ in SiO2 glass took place. The saturation effect of excited-state levels of Tb3+ in SiO2 glass was associated with the slower decay rate of 5D4 level. This result implied that saturation power of Tb3+ in ZnO–SiO2 glass was higher than that in SiO2 glass.

Excited-State Spectroscopy Using Single Spin Manipulation in Diamond

We use single-spin resonant spectroscopy to study the spin structure in the orbital excited state of a diamond nitrogen-vacancy (N-V) center at room temperature. The data show that the excited-state spin levels have a zero-field splitting that is approximately half of the value of the ground state levels, a g factor similar to the ground state value, and a hyperfine splitting approximately 20x larger than in the ground state. In addition, the width of the resonances reflects the electronic lifetime in the excited state. We also show that the spin level splitting can significantly differ between N-V centers, likely due to the effects of local strain, which provides a pathway to control over the spin Hamiltonian and may be useful for quantum-information processing.

Calculations of derivatives of porphin and porphyrazine with an annulated five-membered heteroaromatic ring using a modified INDO method

Quantum-chemical calculations for series of porphin (H2P) and porphyrazine (H2PA) derivatives whose molecules contain a 3,4-annulated five-membered heteroaromatic ring of pyrrole, furan, and thiophene as well as 1,2,5-triazole, 1,2,5-oxadiazole, and 1,2,5-thiadiazole have been carried out by the AM1 and INDO/Sm methods (m means “modified parametrization”). As follows from the unrestricted Hartree-Fock AM1 calculations, the ground state energy of the a isomer is lower than that of the b isomers for all compounds, the a and b isomers being NH isomers with the additional five-membered ring fused to a pyrrolenine or pyrrole ring, respectively. Condensation of the five-membered ring for the b isomers of the H2P derivatives is shown to extend the main conjugation path from 18-membered to 21-membered cyclopolyene. However, the 18-membered cyclopolyene for the a isomers of the H2P derivatives and 16-membered cyclopolyene for both isomers of the H2PA derivatives prove to be isolated from the five-membered ring carrying six π-electrons. Based on INDO/Sm computations of electronic absorption spectra of the H2P and H2PA derivatives, it is shown that the Qx level of the a isomers is sensitive to the nature of the annulated ring whereas the Qy level is practically not shifted. On the contrary, the Qx level of the b isomers is relatively insensitive to the nature of the annulated ring while the Qy level decreases monotonously in the H2P and H2PA series, being the first excited state level for the majority of the derivatives (X is along the NH-HN axis; Y, perpendicular to it). The electronic absorption spectra at the border of the visible and near-UV regions are determined mainly by two high-intensity G → Bx and G → By transitions for the H2P derivatives. However, four intense G → Bx, G → By, G → Nx, and G → Ny transitions are characteristic of the spectra of the H2PA derivatives.

Probing the Dependence of Long-Range, Four-Atom Interactions on Intermolecular Orientation: 2. Molecular Deuterium and Iodine Monochloride

Laser-induced fluorescence and action spectroscopy experiments have identified multiple conformers of the D2...ICl van der Waals complex for both ortho-D2 (o-D2) and para-D2 (p-D2). As with the analogous H2...ICl van der Waals complexes [Darr, J. P.; Crowther, A. C.; Loomis, R. A.; Ray, S. E.; McCoy, A. B. J. Phys. Chem. A 2007, 111, 13387], the C2v conformer with the deuterium molecule localized at the iodine atom end of the dihalogen is significantly more stable than the asymmetric conformer that has the deuterium positioned orthogonally to the ICl bond axis, D0'' = 223.9(2.4) versus 97.3(8)-103.9(3) cm(-1) for p-D2...I(35)Cl(X, v''=0). For both conformers, complexes containing p-D2 are found to be more strongly bound than those with o-D2. The electronically excited D2...ICl(A, v') and D2...ICl(B, v') complexes are found to have equilibrium geometries that are nearly the same as those of the ground-state asymmetric structures. Calculated D2...ICl(B, v'=3) energies and probability amplitudes obtained using a simple scaled He + ICl(B, v'=3) potential provide clues to the nature of the different excited-state levels accessed.

Analysis of the LIF Spectroscopy of Nickel Hydride in 1900021400 cm1

The laser-induced fluorescence (LIF) excitation spectrum of NiH was recorded in the spectral region from 15000 cm1 to 21400 cm1, with the NiH molecules produced by the reaction of sputtered nickel atoms with methanol under supersonic jet conditions. The 1900021400 cm1 portion of the spectrum of NiH is reported for the first time. Twenty-four bands were observed and classified into seven electronic transitions. Every band was rotationally analyzed. Higher vibrational levels of many excited states, A, B, D, E, F, and G, were observed and the complete set of spectroscopic parameters, vibrational frequency, unharmonic constant, rotational constant, and equilibrium length of these states were obtained. Some bands were reassigned.

Electromagnetically induced transparency and retrieval of light pulses in a {lambda}-type and a V-type level scheme in Pr{sup 3+}:Y{sub 2}SiO{sub 5}

We examine electromagnetically induced transparency (EIT), the optical preparation of persistent nuclear spin coherences and the retrieval of light pulses both in a {lambda}-type and a V-type coupling scheme in a Pr{sup 3+}:Y{sub 2}SiO{sub 5} crystal, cooled to cryogenic temperatures. The medium is prepared by optical pumping and spectral hole burning, creating a spectrally isolated {lambda}-type and a V-type system within the inhomogeneous bandwidth of the {sup 3}H{sub 4} {r_reversible} {sup 1}D{sub 2} transition of the Pr{sup 3+} ions. By EIT, in the {lambda}-type scheme we drive a nuclear spin coherence between the ground-state hyperfine levels, while in the V-type scheme we drive a coherence between the excited-state hyperfine levels. We observe the cancellation of absorption due to EIT and the retrieval of light pulses in both level schemes. This also permits the determination of dephasing times of the nuclear spin coherence, either in the ground state or the optically excited state.

Electromagnetically induced transparency and retrieval of light pulses in a Λ-type and a V-type level scheme in Pr3+:Y2SiO5

We examine electromagnetically induced transparency (EIT), the optical preparation of persistent nuclear spin coherences and the retrieval of light pulses both in a Λ-type and a V-type coupling scheme in a Pr3+:Y2SiO5 crystal, cooled to cryogenic temperatures. The medium is prepared by optical pumping and spectral hole burning, creating a spectrally isolated Λ-type and a V-type system within the inhomogeneous bandwidth of the 3H4 ↔ 1D2 transition of the Pr3+ ions. By EIT, in the Λ-type scheme we drive a nuclear spin coherence between the ground-state hyperfine levels, while in the V-type scheme we drive a coherence between the excited-state hyperfine levels. We observe the cancellation of absorption due to EIT and the retrieval of light pulses in both level schemes. This also permits the determination of dephasing times of the nuclear spin coherence, either in the ground state or the optically excited state.

Control of excited-state population and vibrational coherence with shaped-resonant and near-resonant excitation

We investigated numerically and experimentally the enhancement of vibrational coherence and population transfer in solution using tailored pulses. The general control mechanism is based on the precise control of the absorption after excitation with multipulses. Transient absorption was used as an experimental method to quantify the enhancement after the excitation with a shaped pump pulse in the low-pulse energy regime. A density-matrix approach was used to investigate the effect of the shaped excitation of a four-level system (two ground-state vibrational levels + two excited-state vibrational levels). Density-matrix simulation results suggest similar wavelength dependence as observed in the transient absorption experiment. The results show that enhancement of population transfer and vibrational coherence depends crucially on the overlap between the excitation pulse spectrum and the molecular absorption band.

Impact of Methyl Rotor in the Excited State Level Mixing of Doubly Hydrogen-Bonded Complexes of 2-Pyridone

We have presented in this paper the laser-induced fluorescence excitation and resolved fluorescence spectra of five 1:1 hydrogen-bonded complexes of 2-pyridone (2PY) with formic acid (FA), acetic acid (AA), propanoic acid (PA), formamide (FM), and acetamide (AM). The resolved fluorescence spectra, measured following excitation to different single vibronic levels of the dimers indicate that the intermolecular hydrogen bond vibrations undergo mixing with a number of intramolecular modes of the 2PY moiety in the excited state. A comparison of the emission spectral features of these dimers clearly indicates that the methyl groups belonging to the AA and AM moieties spectacularly accelerate the vibrational energy redistribution (IVR) in the 2PY moiety. On the other hand, although the molecular size of PA is bigger than AA, the spectral features of the 2PY-PA dimer bear signatures of a slower IVR rate compared to those of 2PY-AA. We propose that hyperconjugation of the methyl group with the cyclic hydrogen-bonded network involving AA and AM is responsible for the observed phenomenon.

Probing the Dependence of Long-Range, Four-Atom Interactions on Intermolecular Orientation. 1. Molecular Hydrogen and Iodine Monochloride

The dependence of the long-range interactions between molecular hydrogen and iodine monochloride on the geometry between the molecules is investigated. Laser-induced fluorescence and action spectroscopy experiments have identified multiple conformers of the o,p-H2...I35,37Cl(X,v' '=0) van der Waals complexes. A conformer with the hydrogen molecule localized at the iodine end of the dihalogen, most likely with C2v symmetry, is significantly more stable than an asymmetric conformer with the hydrogen localized in the well oriented orthogonally to the I-Cl bond axis, D0' ' = 186.4(3) cm-1 versus 82.8(3) <or= D0' ' <or= 89.6(3) cm-1. Complexes containing the o-H2(j=1) species are more strongly bound than those with p-H2(j=0). The electronically excited o,p-H2...I35Cl(A,v') and o,p-H2...I35,37Cl(B,v') complexes are found to have preferred asymmetric structures with binding energies bracketed between 73.7-80.5 and 69.5-76.3 cm(-1) for o-H2... I35Cl(A,v'=23) and o-H2...I35Cl(B,v'=3), respectively. Calculations of the H2...I35Cl(B,v'=3) intermolecular vibrational energies and probability amplitudes undertaken using a scaled He + ICl(B,v'=3) potential enable us to make tentative assignments of the excited-state levels experimentally accessed.

Determination of the Formation of Dark State via Depleted Spontaneous Emission in a Complex Solvated Molecule

We present a general two-color two-pulse femtosecond pump-dump approach to study the specific population transfer along the reaction coordinate through the higher vibrational energy levels of excited states of a complex solvated molecule via the depleted spontaneous emission. The time-dependent fluorescence depletion provides the correlated dynamical information between the monitored fluorescence state and the SEP "dumped" dark states, and therefore allow us to obtain the dynamics of the formation of the dark states corresponding to the ultrafast photoisomerization processes. The excited-state dynamics of LDS 751 have been investigated as a function of solvent viscosity and solvent polarity, where a cooperative two-step isomerization process is clearly identified within LDS 751 upon excitation.

Preparation and optical properties of the co-doped ZnTe single crystals

The ZnTe:Co single crystals are obtained by diffusion Co-doping. The spectra of optical density in the range of 2.4–0.38 eV are investigated. It is found that Co-doping of the crystals shifts the absorption edge to the low-energy region. The similarity of optical absorption spectra of the ZnTe:Co and ZnS:Co crystals is established. The observed absorption lines of ZnTe:Co are attributed to the optical transitions of electrons from the level of the ground state 4 A 2(F) of the Co2+ ion to the levels of excited states 4 T 1(P), 4 T 1(F), and 4 T 2(F) split by the spin-orbit interaction.

New erbium complexes emitting in infrared region based on oligothiophene and thiophenefluorene carboxylate

Lanthanide ions emitting in the near-infrared (NIR) region possess an intrinsically small molar absorption coefficient in the ultraviolet (UV)–vis–NIR spectrum, which is unfavourable for pumping efficiency. On the contrary, using organic lanthanide complexes it is possible to populate the excited state levels of the emitting ion through an efficient intramolecular energy transfer from the optically excited ligands, which act as light-harvesting antennae. With the aim of studying and maximizing the transfer to lanthanide metals, we have synthesized oligothiophene and thiophenefluorene ligands bearing carboxylate clamps able to complex erbium and other lanthanide 3 + ions. The complexes of {4′-(hydroxycarbonyl)methyl-[2,2′;5′,2″]terthiophen-3′-yl}acetic acid and 9-(hydroxycarbonyl)-methyl-2,7-dithien-2-yl-[fluoren-9-yl-]acetic acid with Er 3+ and different ancillary ligands have been prepared and their optical properties were carefully studied. Moreover, relaxation dynamics measurements have been carried out on all complexes in order to determine emission lifetimes, which result to be of the order of magnitude 2 μs. Quantum chemical calculations have been performed to explain optical absorption data in terms of different coordination types. The complexes containing phenanthroline/pyridine are modelled by adding to the dianion of the ligand one univalent/divalent counterion. The absorption spectra computed in this way are in close agreement with experiment, and the univalent→divalent theoretical wavelength shift goes in the right direction. The addition of a counterion has an even bigger effect on the triplet states, and hence on their matching with the emitting states of the ion.

On a possible variation of the proton-to-electron mass ratio: H 2 spectra in the line of sight of high-redshift quasars and in the laboratory

Recently the finding of an indication for a decrease of the proton-to-electron mass ratio μ = m p/ m e by 0.002% in the past 12 billion years was reported in the form of a Letter [E. Reinhold, R. Buning, U. Hollenstein, P. Petitjean, A. Ivanchik, W. Ubachs, Phys. Rev. Lett. 96 (2006) 151101]. Here we will further detail the methods that led to that result and put it in perspective. Laser spectroscopy on molecular hydrogen, using a narrow-band and tunable extreme ultraviolet laser system at the Laser Centre Vrije Universiteit Amsterdam, results in transition wavelengths of spectral lines in the B 1 Σ u + - X 1 Σ g + Lyman and C 1 Π u - X 1 Σ g + Werner band systems at an accuracy of (4–11) × 10 −8, depending on the wavelength region. This corresponds to an absolute accuracy of 0.000004–0.000010 nm. A database of 233 accurately calibrated H 2 lines is presented here for future reference and comparison with astronomical observations. Recent observations of the same spectroscopic features in cold hydrogen clouds at redshifts z = 2.5947325 and z = 3.0248970 in the line of sight of two quasar light sources (Q 0405−443 and Q 0347−383) resulted in 76 reliably determined transition wavelengths of H 2 lines at accuracies in the range 2 × 10 −7 to 1 × 10 −6. Those observations were performed with the Ultraviolet and Visible Echelle Spectrograph at the Very Large Telescope of the European Southern Observatory at Paranal, Chile. A third ingredient in the analysis is the calculation of an improved set of sensitivity coefficients K i , a parameter associated with each spectral line, representing the dependence of the transition wavelength on a possible variation of the proton-to-electron mass ratio μ. The new model for calculation of the K i sensitivity coefficients is based on a Dunham representation of ground state and excited state level energies, derived from the most accurate data available in literature for the X 1 Σ g + ground electronic state and the presently determined level energies in the B 1 Σ u + and C 1Π u states. Moreover, the model includes adiabatic corrections to electronic energies as well as local perturbation effects between B and C levels. The full analysis and a tabulation of the resulting K i coefficients is given in this paper. A statistical analysis of the data yields an indication for a variation of the proton-to-electron mass ratio of Δ μ/ μ = (2.45 ± 0.59) × 10 −5 for a weighted fit and Δ μ/ μ = (1.99 ± 0.58) × 10 −5 for an unweighted fit. This result, indicating the decrease of μ, has a statistical significance of 3.5 σ. Mass-variations as discussed relate to inertial or kinematic masses, rather than gravitational masses. Separate treatment of the data gives a similar positive result for each of the quasars Q 0405−443 and Q 0347−383. The statistical analysis is further documented and possible systematic shifts underlying the data, with the possibility of mimicking a non-zero Δ μ/ μ value, are discussed. The observed decrease in μ corresponds to a rate of change of d ln μ/d t = −2 × 10 −15 per year, if a linear variation with time is assumed. Experiments for detecting a possible variation of μ in the modern epoch via ultra-precision experiments on H 2 quadrupole transitions are proposed.

Temperature dependence of very deep emission from an exciton bound to an isoelectronic defect in polycrystalline CuInS2

Zero-phonon lines (ZPLs) of deep exciton bound to isoelectronic deep-donor–deep-acceptor pair in CuInS2 are studied by photoluminescence. These ZPLs have peak positions at 0.6241eV (A line) and 0.6220eV (B line), followed by two series of phonon replicas with phonon energies of 8 and 40.5meV. Temperature dependence of the intensity of these ZPLs is explained by electron-phonon coupling to a single phonon mode with energy of 8meV and shows that the lines are originated from two excited state levels of the same exciton. The (anomalously strong) temperature broadening of ZPLs follows ∼T2.6 law and can be explained by assuming a strong vibronic coupling between two excited states.

Fluorescence excitation and single vibronic level emission spectroscopy of the ÃA″1←X̃A′1 system of CHCl

We report new fluorescence excitation and single vibronic level emission spectra of the A (1)A(")<-->X (1)A(') system of CHCl. A total of 21 cold bands involving the pure bending levels 2(0) (n) with n=1-7 and combination bands 2(0) (n)3(0) (1)(n=4-7), 2(0) (n)3(0) (2)(n=4-6), 1(0) (1)2(0) (n)(n=5-7), 1(0) (1)2(0) (n)3(0) (1)(n=4-6), and 1(0) (1)2(0) (n)3(0) (2)(n=4) were observed in the 450-750 nm region; around half of these are reported and/or rotationally analyzed here for the first time. Spectra were measured under jet-cooled conditions using a pulsed discharge source, and rotational analysis typically yielded band origins and rotational constants for both isotopomers (CH(35)Cl,CH(37)Cl). The derived A (1)A(") vibrational intervals are combined with results of Chang and Sears to determine the excited state barrier to linearity [V(b)=1920(50) cm(-1)]. The A (1)A(") state C-H stretching frequency is determined here for the first time, in excellent agreement with ab initio predictions. Following our observation of new bands in this system, we obtained the single vibronic level (SVL) emission spectra which probe the vibrational structure of the X (1)A(') state up to approximately 9000 cm(-1) above the vibrationless level. The total number of X (1)A(') levels observed is around three times than that previously reported, and we observe five new a (3)A(") state levels, including all three fundamentals. The results of a Dunham expansion fit of the ground state vibrational term energies, and comparisons with the previous experimental and recent high level ab initio studies, are reported. Our data confirm the previous assignment of the a (3)A(") origin, and our value for T(00)(a-X)=2172(2) cm(-1) is in excellent agreement with theory. By exploiting SVL spectra from excited state levels with K(a) (')=1, we determine the effective rotational constant (A-B) of the triplet origin, also in good agreement with theory. Our results shed new light on the vibrational structure of the X (1)A('), A (1)A("), and a (3)A(") states of CHCl, and, more generally, spin-orbit coupling in the monohalocarbenes.