Observed Emission Spectra Research Articles

Two-photon excitation of excitons in CuCl in total reflection geometry.

We have observed emission spectra of a CuCl film on a TiO2 prism surface(110) associated with the two-photon excitation of the exciton system in total reflection geometry. The I1 bound exciton emission, which resonantly appeared at the two-photon excitation of the Z3-longitudinal excitons and Z1,2-exciton band, was observed. The dependence of the emission intensities on the polarization of the excitation light was explained from the field intensity and the penetration depth of the evanescent light in CuCl accompanying the totally reflected light at the TiO2/CuCl interface.

Low threshold distributed feedback lasers fabricated from blends of conjugated polymers: Reduced losses through Förster transfer

We report on low threshold photopumped amplified spontaneous emission (ASE) in blends of derivatives of poly (p-phenylene vinylene) and distributed feedback (DFB) lasers fabricated from the same materials. Förster energy transfer is used to spectrally shift the emission away from the absorption band, thereby reducing the optical losses. The concentration of the guest polymer in the blend determines the rate of energy transfer and, thereby, has a strong effect on the observed emission spectrum. The photoluminescence quantum efficiencies (ηPL) of the blends are higher than the ηPL of the pure emissive species (ηPL decreases with increasing amount of the guest polymer in the blends). The blends exhibit optical losses ∼3 cm−1 compared to ∼85 cm−1 in pure host. As a result, the ASE thresholds are reduced from 5000 W/cm2 in the host to 200 W/cm2 in the blends. The corresponding lasing threshold in the DFB structures is 100 W/cm2.

Ab Initio Calculations on PO2 and Anharmonic Franck−Condon Simulations of Its Single-Vibrational-Level Emission Spectra

Geometry optimization and harmonic vibrational frequency calculations were carried out on some low-lying electronic states of PO2 at the CIS, CASSCF, MP2, and RCCSD(T) levels with various standard basis sets of at least valence triple-ζ quality. Relative electronic energies, including vertical excitation energies from the X̃2A1 state {with the electronic configuration of ...(7a1)2(8a1)1} and Te values, were computed at the RCCSD(T) and CASSCF/MRCI levels with basis sets of up to aug-cc-pVQZ quality. These computed results, particularly the computed Te values, suggest that the upper electronic state of the laser induced fluorescence (LIF) and single-vibrational-level (SVL) emission spectra of PO2 reported recently by Lei et al. [J. Phys. Chem. A 2001, 105, 7828] is the 22A1 state of PO2 {with the electronic configuration of ...(7a1)1(8a1)2}. RCCSD(T)/aug-cc-pVQZ and CASSCF/MRCI/aug-cc-pVQZ(no g) energy scans were carried out on the X̃2A1 and 22A1 states of PO2, respectively, in the symmetric stretching and bending coordinates. Franck−Condon factors (FCFs) between the two states, which allow for the Duschinsky and anharmonic effects, were calculated employing the potential energy functions obtained from the ab initio scans. Comparison between the simulated spectra based on the computed FCFs and observed SVL emission spectra led to reassignments of the vibrational designations of the emitting SVLs in the upper state. On the basis of the excellent agreement between the simulated spectra for the revised SVLs and the observed emission spectra, the electronic transition involved in the LIF and SVL emission spectra reported by Lei et al. is confirmed to be 22A2−X̃2A1 of PO2. Following the revised vibrational assignments of the upper electronic state in the SVL emissions, the vibrational assignments of the LIF excitation bands given by Lei et al. are revised and a revised T0 value of 30660 cm-1 is estimated for the 22A1 state of PO2. In addition, employing the iterative Franck−Condon analysis (IFCA) procedure in the simulation of the SVL emission spectra, the equilibrium geometry of the 22A1 state of PO2 is derived for the first time (re = 1.560 Å; θe = 116.5°).

Emission spectroscopy, harmonic vibrational frequencies, and improved ground state structures of jet-cooled monochloro- and monobromosilylene (HSiCl and HSiBr)

The ground state harmonic frequencies of gas phase H/DSi35Cl and H/DSi79Br have been determined by exciting single vibronic bands of the à 1A″–X̃ 1A′ electronic transition and recording the dispersed fluorescence. The jet-cooled radicals were produced in a pulsed discharge jet using H/DSiX3 (X=Cl or Br) precursors. The emission data were fitted to an anharmonic model and a normal coordinate analysis of the harmonic frequencies allowed the determination of five of the six force constants of each molecule. Using previously obtained v″=0 rotational constants and the improved force fields, average (rz) and estimated equilibrium (rez) structures were calculated for both monohalosilylenes. The validity of the force constants was evaluated by comparing calculated and observed zero-point inertial defects and by simulating the Franck–Condon profiles of the observed emission spectra in the harmonic approximation.

Elementary processes of photolysis in lead halide crystals

Elementary processes of photolysis in lead halide crystals

Photoluminescence of rapid-thermal annealed Mg-doped GaN films

Photoluminescence of rapid-thermal annealed Mg-doped GaN films

Hot bands of (f, f ∗) emission from ytterbium(III) porphyrins in solution

Hot bands of (f, f ∗) emission from ytterbium(III) porphyrins in solution

Theoretical and experimental research on excimer like (N 2) 2 dimer: potential energy curves and spectra

Theoretical and experimental research on excimer like (N 2) 2 dimer: potential energy curves and spectra

Velocity Modification of HiPower Spectrum

The distribution of atomic hydrogen in the Galactic plane is usually mapped using the Doppler shift of 21 cm emission line, and this causes the modification of the observed emission spectrum. We calculate the emission spectrum in velocity slices of data (channel maps) and derive its dependence on the statistics of velocity and density fields. We find that, (1) if the density spectrum is steep, i.e., n < -3, the large k asymptotics of the emissivity spectrum are dominated by the velocity fluctuations; and (2) the velocity fluctuations make the emission spectra shallower, provided that the data slices are sufficiently thin. In other words, turbulent velocity creates small-scale structure that can erroneously be identified as clouds. The effect of thermal velocity is very similar to the change of the effective slice thickness, but the difference is that, while an increase of the slice thickness increases the amplitude of the signal, the increase of the turbulent velocity leaves the measured intensities intact while washing out fluctuations. The contribution of fluctuations in warm H I is suppressed relative to those in the cold component when the velocity channels used are narrower than the warm H I thermal velocity and small angular scale fluctuations are measured. We calculate how the spectra vary with the change of velocity slice thickness and show that the observational 21 cm data is consistent with the explanation that the intensity fluctuations within individual channel maps are generated by turbulent velocity fields. As the thickness of velocity slices increases, density fluctuations begin to dominate emissivity. This allows us to disentangle velocity and density statistics. The application of our technique to Galactic and SMC data reveals spectra of density and velocity with power law indexes close to -11/3. This is a Kolmogorov index, but the explanation of the spectrum as due to the Kolmogorov-type cascade faces substantial difficulties. We generalize our treatment for the case of a statistical study of turbulence inside individual clouds. The mathematical machinery developed is applicable to other emission lines.

Microdischarge Optical Emission Spectroscopy as a Novel Diagnostic Tool for Metalorganic Chemical Vapor Deposition of (Ba,Sr)TiO3 Films

Microdischarge optical emission spectroscopy (µD-OES) was developed as a diagnostic tool for analyzing chemical reactions in metalorganic chemical vapor deposition of (Ba,Sr)TiO3 films. The degree of thermal decomposition of the CVD source molecules was obtained from the observed emission spectra of the small plasma excited at the OES sensor head. According to the observation of SrII and BaII emission lines, Sr(DPM)2 and Ba(DPM)2 decompose at the gas temperatures of 270°C and 280°C, respectively. The temperature dependence of the observed emission intensity showed a behavior similar to that of the deposition rate. The oxidation of the CVD source molecules in the gas phase was also investigated by observing the change in the emission spectra due to the addition of oxygen gas. We also measured the spatial distribution of the source molecules by radially moving the OES sensor head, and compared it with the uniformity of the film thickness.

Infrared spectral sequence of quenched carbonaceous composite subjected to thermal annealing

We investigate the spectroscopic alteration through thermal annealing on the quenched carbonaceous composite (QCC) produced from hydrocarbon plasma. The emission and absorption spectra of QCC samples annealed at various temperatures indicate that the proportion of aliphatic C-H bonds in QCC decreases relative to aromatic C-H bonds with increase of annealing temperature. By comparing the spectra of annealed QCC with observed emission spectra of proto-planetary nebulae, similarity between the spectral sequence obtained in the laboratory and that in the observational data is clearly noticed. On this basis, we discuss a simple evolutional scenario of carbon dust in circumstellar environment around cool evolved stars.

Luminescence studies of dinuclear gold(I) phosphor-1,1-dithiolate complexes

Luminescence studies of dinuclear gold(I) phosphor-1,1-dithiolate complexes

Intrasubband fast absorption and emission of terahertz radiation by hot electrons in GaAs/AlGaAs MQW

Intrasubband fast absorption and emission of terahertz radiation by hot electrons in GaAs/AlGaAs MQW

O‐Mode Emission at the Io Torus: A Real or Virtual Source?

We examine the nature of an ordinary (o‐mode) emission observed near the Io plasma torus during the 1992 Ulysses encounter with Jupiter. The emission appears to intensify by factors of 10–100 in local torus density depletions. We examine whether these intensifications are due to local generation within the density depletion or reflection of a remotely generated emission. Based on the observed emission spectra, we find that a virtual source is most consistent with the character of the local enhancements. This virtual source observation near the dense torus may be relevant to the understanding of a newly discovered torus‐related hectometric emission by the Galileo orbiter.

Energy Transfer between Mn Ions in Semimagnetic Semiconductors

Time-resolved measurement is performed for photoluminescence around 2.0 eV which originates from internal transition between 3d multiplet states in Mn based semimagnetic semiconductors. Observed emission spectra show red shift with delay time after excitation. Larger shift is observed in the sample with larger width of the emission spectrum, which implies that the shift is caused by the energy relaxation in the inhomogeneous distribution of the Mn energies. To confirm this, we perform simple Monte-Carlo simulation in a wide range of time scale. The results well explain the magnitude of the shift and its logarithmic dependence on delay time. The dependences on excitation energy, temperature and pressure are also investigated.

Room-temperature fluorescence characteristics of single dye molecules adsorbed on a glass surface

Measurements of the total fluorescence and fluorescence spectra from single carbocyanine dye molecules (DiIC12) as a function of time reveal a wide range of phenomena. Discrete jumps in the fluorescence intensity from single molecules on a glass surface have been observed with correlation times spanning several orders of magnitude (1 ms–10 s). We propose a model for these fluctuations in which two or more ground state potential minima are accessed by twists of the chromophore backbone that alter the quantum efficiency of emission as well as the emission spectrum. Monte Carlo simulations based on this model are shown which qualitatively match experimental data. In addition, we observed emission spectra which range in shape from narrow, well-separated vibronic bands to a broad, featureless band. The distribution of emission parameters from different molecules, not obtained from ensemble measurements, indicates an abundance of distinct nanoenvironments of the glass surface sampled by the adsorbed molecules.

Formation of XeBr*, Xe*, and Br* by the Xe+(2P1/2)/Br−/He and Xe+(2P3/2)/Br−/He three-body ionic-recombination reactions in a helium flowing afterglow

Three-body ionic-recombination reactions of Xe+/Br−/He leading to XeBr* excimers and their predissociation products (Xe* and Br*) have been studied by observing emission spectra in a He flowing afterglow. The branching ratios of XeBr(B):XeBr(D):Xe(6s 3P1,6p 1D2):Br(5p) in the Xe+(2P1/2)/Br−/He reaction are 0.65:0.077:0.087:0.19, while those of XeBr(B):XeBr(C):XeBr(D):Xe(6s 3P1):Br(5s) in the Xe+(2P3/2)/Br−/He reaction are 0.87:0.12:0.0040:0.0014:0.0067, respectively. The large relative formation rate of XeBr(B) in the Xe+(2P1/2)/Br−/He reaction indicated that a breakdown of the ion configuration of Xe+ occurs significantly in the Xe+(2P1/2) reaction. The XeBr(B) state is probably formed through multiple collisions with third-body He atoms, which cause a trajectory change from the entrance V[Xe+(2P1/2),Br−] potential to exit V[Xe+(2P3/2),Br−] ionic potentials via predissociation V(Xe*,Br) potentials. The large relative formation rates of XeBr(B,C) in the Xe+(2P3/2)/Br−/He reaction indicated that the ion configuration of Xe+ is conserved well in the Xe+(2P3/2) reaction. The electronic state distribution of Br(5p) in the Xe+(2P1/2)/Br−/He reaction is nonstatistical, providing any preference for doublet, quartet, or for particular J states. It was concluded that most of Xe* and Br* are formed via predissociation of vibrationally excited XeBr* at long internuclear distances above 20 Å.

Lowest Excited State of Oxovanadyl(IV) Tetraphenylporphyrin

The excited-state relaxation dynamics and pathways of oxovanadyl(IV) tetraphenylporphyrin (OVIVTPP) have been investigated by nanosecond time-resolved and steady-state emission, transient absorption, and transient resonance Raman spectroscopies. At room temperature, the emission spectrum shows a single broad featureless band centered near 790 nm in noncoordinating solvents such as toluene and benzene and at 814 nm in tetrahydrofuran (THF), whereas at 77 K the emission bands in the same solvents exhibit blue-shifts to 745 and 784 nm, respectively. Furthermore, the emission decay time in benzene increases from 40 to 60 ns with a decrease in temperature from 323 to 268 K. In contrast, the decay time in THF is ca. 10 ns, which is almost independent of temperature. The energy separation between the tripdoublet state (2T(π,π*)) and the tripquartet one (4T(π,π*)) under the proposed relaxation scheme of photoexcited OVIVTPP has been estimated to be ca. 500 cm-1 in benzene and toluene. The transient absorption spectra at room temperature denote a broad featureless absorption centered at around 480 nm with a ground-state bleaching at 555 nm. All the spectroscopic results including the transient Raman spectra led us to conclude that the electronic nature of the lowest excited state should be the tripquartet state (4T(π,π*)) at ambient temperature. The decay times for both photoinduced absorption and bleaching are similar and also in good accordance with the emission decay times as long as temperature and solvent are the same. The time-resolved emission spectra and wavelength dependent decay kinetics at 77 K reveal that the observed emission spectra apparently originate from three different emitting species. These observations are discussed in terms of postulating a quenching state (Q), which is thermally accessible from the tripdoublet state (2T(π,π*)) of OVIVTPP at room temperature.

New Precursor Routes to Nanocrystalline Cubic/Hexagonal Gallium Nitride, GaN

ABSTRACTTwo precursor routes culminating in bulk nanocrystalline gallium nitride materials are reported, with emphasis on the materials' XRD/crystalline features and photoluminescence (PL). First, the new polymeric gallium imide, {Ga(NH)3/2}n, can be converted to nanocrystalline, cubic/hexagonal GaN ranging in color from yellow to light gray. Second, a new route to gallazane, [H2GaNH2]x, from the combination of LiGaH4 and NH4X (X = Cl, Br) in Et2O is shown to result in a material that slowly converts to a polymeric solid via H2 and NH3 elimination-condensation pathways. Both the gallazane and the polymeric solid are pyrolyzed to dark gray nanocrystalline, phase-inhomogeneous GaN as above. Specific variations in the pyrolysis conditions enable some control over the particle nanosize and a degree of crystalline phase-inhomogeneity of the materials. These nanophase GaN materials have also been characterized by room temperature photoluminescence (PL) measurements. In general, the observed emission spectra are strongly dependent on pyrolysis temperature and typically exhibit weak defect yellow-green emission. While the as-prepared GaN does not exhibit band-edge PL, a brief hydrofluoric acid etch yields nanophase GaN exhibiting an intense blue-emitting PL spectrum with an emission maximum near 420 nm.

Bio-material laser action enforced by mixed highlyscattering Intralipid in microdroplet containing pigment extracted from biological tissues

Microdroplets that contain a mixture of highly scattering Intralipid-10%, with pigment extracted from biological tissues were used to observe the first laser action that exhibits well-defined lasing thresholds. The authors confirmed experimentally that the addition of the highly scattering Intralipid-10% can assist this bio-material laser action in the microdroplets, otherwise no laser emission was originally generated. The pigment was identified to be chlorophyll, included in the radish green leaves from the observed emission spectra.