1A1 Transition Research Articles

Environmentally friendly Rb3V5O14 fluorescent red pigment

Rb3V5O14, which was successfully synthesized by a water assisted solid state reaction (WASSR) method, is a fluorescent red pigment that is environmentally friendly. The Rb3V5O14 fluorescent pigment showed a strong optical absorption in the green light region due to the energy transfer from O2− 2p orbital to V5+ 3d orbital of VO5 polyhedra and band-gap energy of Rb3V5O14 was 2.02 eV. The fluorescent pigment presented a broad red emission peaked at 625 nm due to the 3T2 → 1A1 and 3T1 → 1A1 transitions of the [VO4]3− group. The Rb3V5O14 fluorescent pigment showed a bright-vivid red body color, and the L*, a*, and b* values were 47.4, +45.9, and +34.4, respectively.

Electrospinning fabrication and luminescence of La3(BWO9):Tb3+ nanofibers

La3(BWO9):Tb3+ nanofibers were fabricated by an electrospinning process. The XRD patterns of the obtained fibers indicate that the incorporation of Tb3+ ions will not change the phase of La3(BWO9). The excitation spectrum monitored at 547 nm consists of excitation bands originating from 1T1 → 1A1 transition of O2− → W6+ in the WO6 group and 4f8 → 4f75d1/4f8 transitions of Tb3+. Upon the excitation at 362 nm, La3(BWO9):Tb3+ fibers show emission bands originating from the 5D4 → 7Fj (j = 6, 5, 4 and 3) transitions of Tb3+. The decay characteristics of La3BWO9:Tb3+nanofibers indicate that Tb3+ ions occupy one site in the host lattice.

Synthesis, energy transfer and luminescence properties of KSrVO4:Eu3+ red phosphor

KSrVO4:Eu3+ phosphors are synthesized by solid-state reaction method in air. Host KSrVO4 under excitation at 345 nm emits green–yellow light with the CIE chromaticity coordinates (0.3466, 0.4425), and its broad emission band peaking at ~545 nm covers the range 400–750 nm due to 3T1,2 → 1A1 transitions in [VO4]3− group. KSrVO4:Eu3+ phosphor under excitation at 315 and 394 nm shows red emission with the CIE chromaticity coordinates (0.6279, 0.3717), and the emission spectra in the range of 560–750 nm contains four narrow emission bands owing to 5D0 → 7FJ (J = 1, 2, 3, and 4) transitions of Eu3+ ion, respectively. The optimal Eu3+ doping concentration is ~4 mol%. The lifetime decreases from 0.991 to 0.893 ms with increasing Eu3+ concentration within the range 0.5–6 mol%. The possible luminous mechanism is analyzed by the simplified energy level diagrams of VO43− group and Eu3+ ion, and energy transfer process in KSrVO4:Eu3+ phosphor. The experimental results indicate that KSrVO4:Eu3+ phosphor will be possible to be used as red phosphor candidate for white light-emitting diode (LED) based on ultraviolet (~315 nm) and near ultraviolet (~395 nm) LED chips.

Tunable optical properties of multiphase ZnO–V2O5 polycrystalline powders

Bright yellow and white-yellow light emitting ZnO–V2O5 polycrystalline powders are synthesized by engineering zinc oxide and different zinc vanadate phases. Emission characteristics strongly depend on different zinc vanadate phases. The bright yellow emission is originated from the 3T2→1A1 and 3T1→1A1 transitions in the VO4 tetrahedra of zinc vanadate phase. White-yellow emission is the combination of blue and green emissions due to native point defects of ZnO and the yellow and red emission from zinc vanadate.

Controllable route to barium molybdate crystal and their photoluminescence

A simple precipitation route has been developed to synthesize BaMoO4 with different morphologies, such as flower-like spheres, spindle-like and octahedron crystals, by using a novel organic compounds poly-(styrene-alt-maleic acid) (PSMA) as crystal growth modifier. The concentrations of PSMA and reactants have significant influences on the morphology control of BaMoO4. PSMA efficiently controls the morphology by inhibiting the oriented growth direction. The photoluminescence spectra show broad green emission at 530nm, which is attributed to the 1T2→1A1 transition in the intrinsic MoO42− group.

Optical spectrum of Si3C, and a re-analysis of the [formula omitted] transition

The electronic spectrum of Si3C has been measured in the 710–250nm region by resonant two-color two-photon ionization spectroscopy. In addition to the strong C∼1B1←X∼1A1 transition near 400nm, evidence is found for two weaker features: a broad, largely structureless band near 625nm, which is assigned to A∼1B1←X∼1A1, and a band near 333nm with partially-resolved vibronic structure, which we assign to E∼1B1←X∼1A1. Assignment of the transitions and analysis of their vibrational structure is supported by equation-of-motion coupled cluster calculations. Re-measurement and re-analysis of the C∼←X∼ transition at higher spectral resolution and signal-to-noise ratio than that reported previously (Stanton et al., 2005) allows essentially all of the vibronic features to be assigned with confidence.

Luminescence properties of Li2Ca2ScV3O12 and Li2Ca2ScV3O12:Eu3+ synthesized by solid-state reaction method

Li2Ca2ScV3O12 and Eu3+ doped Li2Ca2ScV3O12 have been synthesized by a high temperature solid-state reaction method. The as-prepared compounds have the garnet-type structure by the X-ray diffraction (XRD) analysis. Li2Ca2ScV3O12 can be self-excited by the UV light ranging from 200 to 400nm, and it shows the broad-band greenish yellow emission originating from the VO43- charge transition (CT), which contains two fitting bands with peaks at 510nm and 569nm, corresponding to the 3T2→1A1 and 3T1→1A1 transitions of VO43-. Eu3+ doped Li2Ca2ScV3O12 phosphor shows characteristic broad-band emission of VO43- and the line-type emission of Eu3+ in the red region, which exhibits yellow emission upon the 365nm UV light. The CIE coordinates and the lifetimes of the samples have been also investigated.

Synthesis and Structural Characterization of the Mononuclear Cobalt(II) Complex: {5,5′-Dihydroxy-2,2′-[o-phenylene-bis(nitrilomethylene)]diphenolato}cobalt(II) Dihydrate

The Schiff base ligand H2L·C2H5OH derived from the condensation reaction between o-phenylenediamine and 2,4-dihydroxybenzaldehyde as well as its mononuclear complex [CoL]·2H2O have been synthesized and characterized by X-ray crystallography, IR, 1H NMR and UV–Vis analyses, and density functional theory (DFT B3LYP) calculations. The CoII ion has a slightly distorted square-planar coordination provided by tetradentate dianionic N2O2 ligand L2−. The spin state of the complex was determined as being S = 1/2. On the basis of DFT calculations, the UV–Vis absorption bands of the ligand can be assigned to the 1A1 → 1B2 (two) and 1A1 → 1A1 transitions, while for complex they correspond to the 2A2 → 2B1 (two) and 2A2 → 2A2 ones. Index Abstract The Schiff base ligand H2L·C2H5OH derived from the condensation reaction between o-phenylenediamine and 2,4-dihydroxybenzaldehyde as well as its mononuclear complex [CoL]·2H2O have been synthesized and characterized by X-ray crystallography, IR, 1H NMR and UV–Vis analyses, and density functional theory (DFT B3LYP) calculations.

Color tunable phosphor CaMoO4:Eu3+,Li+ via energy transfer of MoO42−–Eu3+ dependent on morphology and doping concentration

The cooling rate and the solubility of molybdate in molten salt play crucial roles on the microscopic morphologies and photoluminescence (PL) properties of the phosphor CaMoO4:Eu3+,Li+. Undoped CaMoO4 exhibits self-activated green PL with a broad emission band which is assigned to the spin forbidden 3T1,2–1A1 transition of the MoO42− complex. The strong UV absorption of undoped CaMoO4 is originated from the charge transfer from O2− ligands to the central Mo6+ ions inside MoO42− group. The emission of the phosphor CaMoO4:Eu3+,Li+ obtained by molten salt synthesis (MSS) at 900°C is composed of a broad green emission from MoO42− and a group of sharp red emission peaks from f–f transitions of Eu3+. Efficient energy transfer from MoO42− to Eu3+ is responsible for the increased red PL of the phosphor. The dependence of energy transfer efficiency on the processing conditions and doping concentration has been investigated.

Imaging H2O Photofragments in the Predissociation of the HCl−H2O Hydrogen-Bonded Dimer

The state-to-state vibrational predissociation (VP) dynamics of the hydrogen-bonded HCl-H(2)O dimer was studied following excitation of the dimer's HCl stretch by detecting the H(2)O fragment. Velocity map imaging (VMI) and resonance-enhanced multiphoton ionization (REMPI) were used to determine pair-correlated product energy distributions. Following vibrational excitation of the HCl stretch of the dimer, H(2)O fragments were detected by 2 + 1 REMPI via the C (1)B(1) (000) ← X (1)A(1) (000) transition. REMPI spectra clearly show H(2)O from dissociation produced in the ground vibrational state. The fragments' center-of-mass (c.m.) translational energy distributions were determined from images of selected rotational states of H(2)O and were converted to rotational state distributions of the HCl cofragment. The distributions were consistent with the previously measured dissociation energy of D(0) = 1334 ± 10 cm(-1) and show a clear preference for rotational levels in the HCl fragment that minimize translational energy release. The usefulness of 2 + 1 REMPI detection of water fragments is discussed.

The B 1B1 State of Cyclopropenylidene, c-C3H2

The B 1B1 ← X 1A1 transition of isolated cyclopropenylidene, c-C3H2, has been studied by multiphoton ionization and H-atom photofragment Doppler spectroscopy. The carbene is produced by flash pyrolysis of 1-chlorocycloprop-2-ene. Three bands are observed at 271.0, 266.9, and 264.6 nm. The 271 nm band is assumed to be the origin of the transition, in agreement with TD-DFT computations that yield a vertical excitation energy of 4.74 eV (262 nm). The appearance of H-atom photofragments indicates that c-C3H + H is an important reaction channel at UV excitation energies.

Microwave-assisted synthesis and characterization of SrMoO4 and SrWO4 nanocrystals

SrMoO4 and SrWO4 nanocrystals have been synthesized using Sr(NO3)2 and Na2MeO4 (Me = Mo and W) in ethylene glycol by a microwave irradiation method at 50% of 180 W for 20 min. The product phases were detected using X-ray and selected area electron diffractions. They show the body-centered primitive tetragonal structure with the lattice parameters of a = b = 5.4007 A and c = 12.0330 A for SrMoO4, and a = b = 5.4274 A and c = 11.9241 A for SrWO4. X-ray diffraction patterns of the products, obtained by simulation using CaRIne version 3.1 program, are in accordance with those of the corresponding experiment and International Centre for Diffraction Data. A transmission electron microscope revealed the presence of nanocrystals composing the products, with their sizes in the ranges of 14–40 and 14–38 nm for SrMoO4 and SrWO4, respectively. Six different vibrations of ν 1(A g), ν 3(B g), ν 3(E g), ν 4(B g), ν 2(A g), and ν f.r.(A g) were detected using a Raman spectrometer, and the ν 3(F 2) antisymmetric stretching and ν 4(F 2) bending modes of [MeO4]2− tetrahedrons using a Fourier transform infrared spectrometer. Photoluminescence emissions of SrMoO4 and SrWO4, caused by the 1 T 2 → 1 A 1 transition of electrons, were detected at 410 and 418 nm, respectively.

S 1 ( A 1 1 ) ← S ( A 1 1 ) transition of benzo[g,h,i]perylene in supersonic jets and rare gas matrices

The study of the S1(1A1)<--S0(1A1) transition of benzo[g,h,i]perylene (BghiP, C22H12) in supersonic jets and solid rare gas matrices is reported. In the jet-cooled spectrum, the origin band position is located at 25,027.1+/-0.2 cm-1, the assignment being supported by the analysis of vibrational shifts and rotational band contours. Except for the origin band, which is weak, all bands are attributed to the fundamental excitation of nontotally symmetric b1 vibrational modes of S1. The intensity pattern is interpreted as a consequence of the weak oscillator strength of the electronic transition combined with intensity-borrowing through vibronic interaction between the S1(1A1) and S2(1B1) states. The spectra of the S1(1A1)<--S0(1A1) and S2(1B1)<--S0(1A1) transitions have also been measured for BghiP in solid neon and argon matrices. The comparison of the redshifts determined for either transition reveals that the polarizability of BghiP is larger in its S2 than in its S1 state. Bandwidths of 2.7 cm-1 measured in supersonic jets, which provide conditions relevant for astrophysics, are similar to those of most diffuse interstellar bands. The electronic transitions of BghiP are found to lie outside the ranges covered by present databases. From the comparison between experimental spectra and theoretical computations, it is concluded that the accuracy of empirical and ab initio approaches in predicting electronic energies is still not sufficient to identify astrophysically interesting candidates for spectroscopic laboratory studies.

Configuration interaction oscillator strengths of the H2O molecule: Transitions from the ground to the [formula omitted] and 11B2 excited states

The vertical optical oscillator strength (OOS) at the length (fL) and velocity (fV) forms for the {B∼1A1,C∼1B1,D∼1A1,11B2}←X∼1A1 transitions of H2O were computed employing complete active space self consistent field followed by multireference configuration interaction (CAS/MR-CI) wave functions and d-aug-cc-pVXZ (X=D,T,Q,5) Gaussian basis sets. The computed OOS values at the highest level, namely, CAS-MRCI/d-aug-cc-pV5Z, were (fL value, fV value): B∼1A1 (0.05494, 0.05993), C∼1B1 (0.008700, 0.009634), D∼1A1 (0.04695, 0.04880) and 11B2 (0.01740, 0.01905). These results are compared with previous theoretical and experimental values, with the latter when possible.

Evaluation of low-scaling methods for calculation of phosphorescence parameters

In order to find a methodology that is a compromise between favorable computational scaling and tolerable errors, a series of nonrelativistic approaches for the calculation of radiative phosphorescence lifetimes are benchmarked against fully relativistic four-component results. The study of the a 3A2-X 1A1 transition intensity in the series of H2CX molecules, where X is a chalcogene atom, X={O,S,Se,Te}, indicates a general good agreement between fully relativistic four-component and nonrelativistic perturbation-theoretical calculations. Among the nonrelativistic approaches, the scaled-charge spin-orbit operator approach is recognized as to provide transition matrix elements that are in good agreement with those obtained with the more elaborate Breit-Pauli and atomic mean field spin-orbit operators. This finding supports phosphorescence calculations using the available linear scaling technology for large complexes and, together with effective-core potentials, large complexes including heavy elements.

Ab initio Cluster Calculations for the Absorption Energies of F and F+ Centers in Bulk ZnO.

We present the results of a series of ab initio calculations on the ground states and the low lying excited states of the F and F+ centers in bulk ZnO. Both types of F centers are oxygen vacancies, causing rather strong distortions of the local geometries. The calculations were performed by means of wave function based methods, mostly at the CASSCF level. Dynamic correlation was included for the first two coordination shells of the F centers. The calculated absorption energy for the F+ center (3.19 eV) is in excellent agreement with the experimental value of 3.03 eV. For the emission from the 3T2 state of the F center to the 1A1 ground state we obtained a transition energy of 2.73 eV. Experimentally, a green photoluminescence is observed at 2.38–2.45 eV. We estimated that the errors in our calculation should be even smaller in the latter case than for the F+ state, where the calculated transition energy differs by less than 0.2 eV from the experimental value. Therefore, we assume that the 3T2 to 1A1 transition is not the origin of the green luminescence.

Laser-induced fluorescence excitation and dispersed fluorescence spectroscopy of the Ã(1B1)–X̃(1A1) transition of dichlorocarbene

The A(1B1)–(1A1) transition of jet-cooled CCl2 has been investigated using both laser-induced fluorescence (LIF) excitation and dispersed fluorescence (DF) spectroscopy. DF spectra were taken from over 90 emitting vibronic states over the breadth of the LIF spectrum. 68 ground state vibrational levels were assigned in the C35Cl2 isotopomer and 47 in C35Cl37Cl. The ground state frequencies were fit to an anharmonic potential yielding: ω″1 = 736 cm−1, ω″2 = 338 cm−1, ν″3 = 760 cm−1, x″11 = −3.19 cm−1, x″22 = −0.29 cm−1, x″12 = −1.80 cm−1, x″13 = −5.70 cm−1 and x″23 = −3.80 cm−1. This is the first gas phase measurement of ν″3. Despite the close frequency match between ν″1 and 2ν″2 there was no evidence for Fermi resonance. The intensities of transitions in the DF spectra were analysed to identify the nature of the emitting state. Levels below T00 + 2500 cm−1 in the A state could be assigned simply as combinations and overtones of ν′1 and ν′2. Between T00 + 2500 and T00 + 5300 cm−1 the emission revealed an increasing mixing between levels within the same polyad, i.e., (m,n,0), (m + 1,n − 2,0), (m + 2,n − 4,0) etc, presumably due to Fermi resonance. This mixing becomes so extensive that simple assignment of the emitting states is not possible. Above T00 + 5300 cm−1 only K′ = 0 states could be identified, indicating that the Renner–Teller intersection between the and A states had been exceeded. This intersection is therefore 22 600 cm−1 above the ground state, in excellent agreement with a previous theoretical calculation of 23 000 cm−1.

Ab initio cluster calculations for the absorption energies of F and F+ centers in bulk ZnO

We present the results of a series of ab initio calculations on the ground states and the low lying excited states of the F and F+ centers in bulk ZnO. Both types of F centers are oxygen vacancies, causing rather strong distortions of the local geometries. The calculations were performed by means of wave function based methods, mostly at the CASSCF level. Dynamic correlation was included for the first two coordination shells of the F centers. The calculated absorption energy for the F+ center (3.19 eV) is in excellent agreement with the experimental value of 3.03 eV. For the emission from the 3T2 state of the F center to the 1A1 ground state we obtained a transition energy of 2.73 eV. Experimentally, a green photoluminescence is observed at 2.38-2.45 eV. We estimated that the errors in our calculation should be even smaller in the latter case than for the F+ state, where the calculated transition energy differs by less than 0.2 eV from the experimental value. Therefore, we assume that the 3T2 to 1A1 transition is not the origin of the green luminescence.

Linewidths and line intensity measurements in the weak 3A2(000) ← 1A1(000) band of ozone by pulsed cavity ringdown spectroscopy

Pulsed cavity ringdown spectroscopy in the near‐infrared spectral range was employed to measure linewidths of the 3A2(000) ← 1A1(000) band of ozone in direct comparison with intracavity laser absorption spectroscopy. It is demonstrated that also for a small ratio, V, which is the ratio of the absorption linewidth and the laser bandwidth, correct linewidths can be determined from a forward modeling of the experimental line profiles, taking explicitly into account the laser bandwidth and the cavity modes. The obtained linewidths have been compared with those measured by intracavity laser absorption spectroscopy and found to agree quantitatively within experimental error. Linewidths as a function of pressure have been analyzed to obtain pressure‐broadening coefficients and the effective linewidth at zero pressure, which is a measure for the excited state lifetimes of the ozone in the excited triplet states. The observed linewidths are a direct observable for the intramolecular dynamics in the low‐lying excited 3A2 triplet state of ozone. In any case, the observed lifetimes for the excited 3A2(000) state in the range between 20 and 130 picoseconds (ps) rule out metastability of this state. Beyond linewidth measurements we have also refined the spectroscopic parameters of this electronically excited state and determined the integrated absorption of the corresponding 3A2(000) ← 1A1(000) transition.

Excited state dynamics of Cl2O in the near ultraviolet

The state-resolved and isotope-specific detection of nascent ClO generated from the photodissociation of Cl2O parent molecules is performed by observing single-color (2+1) resonance enhanced multiphoton ionization (REMPI) spectra following excitation in the wavelength range from 336 to 344 nm; additionally state-resolved detection of nascent ClO is performed by observing single-color two photon laser-induced fluorescence. The REMPI spectrum is assigned to the ClO(C 2Σ−,v′=0←X 2ΠΩ,v=0) transition. The population of rotational states up to J=130 is evidence of large rotational excitation induced by a strong dependence of the excited potential energy surface (PES) on the Jacobi angle γ. Formation of the Π3/22 spin-orbit state is preferred: P(2Π1/2):P(2Π3/2)=0.30±0.05 suggesting significant radiationless transfer from the excited PES to closely lying neighboring states. The anisotropy parameter for the transition is determined to be β=0.35 independent of the ClO quantum state. The principal excited electronic state is assigned to a B21←A11 transition, in agreement with recent ab initio calculations. The measured β value is smaller than the limiting value of 1.0, suggesting dynamic reasons and simultaneous excitation to more than one PES. A fast and direct fragmentation process is deduced, where the upper limit for the lifetime of the excited dissociative state is calculated to be 300 fs.