Showing papers on "Photoexcitation published in 1987"
TL;DR: In this paper, the ultrafast relaxation of large organic molecules in solution has been investigated with the transmission correlation technique, and the existence of damped sinusoidal decays after photoexcitation has been verified for several organic dyes.
Abstract: The ultrafast relaxation of large organic molecules in solution has been investigated with the transmission correlation technique. The existence of damped sinusoidal decays after photoexcitation has been verified for several organic dyes. This behavior (the first such decay observed on a femtosecond time scale for any material) is explained as quantum beats. For all molecules examined, we have also observed fast initial exponential decays (<100 fs) in addition to previously known picosecond processes.
130 citations
Journal Article•
TL;DR: In this article, photoexcited chemical vapor deposition (CVD) and etching using synchrotron radiation as an exciting light source were experimentally demonstrated, and reaction models for gas phase excitation and surface excitation were proposed.
Abstract: Photoexcited chemical‐vapor deposition (CVD) and etching using synchrotron radiation as an exciting light source were experimentally demonstrated. CVD of silicon nitride film and etching of Si and SiO2 by SF6+O2 gases are described in detail. In several reaction systems, it was found that the surface photoexcitation was an important mechanism. Reaction models for gas‐phase excitation and surface excitation were proposed.
89 citations
TL;DR: A coloured charge transfer complex formed by adsorption of Fe(CN)64 at the surface of TiO2 particles and electrodes upon photoexcitation injects electrons into the conduction band of this semiconductor with a quantum yield of at least 37%.
Abstract: A coloured charge-transfer complex formed by adsorption of Fe(CN)64– at the surface of TiO2 particles and electrodes upon photoexcitation injects electrons into the conduction band of this semiconductor with a quantum yield of at least 37%.
87 citations
TL;DR: In this paper, photoexcited chemical vapor deposition (CVD) and etching using synchrotron radiation as an exciting light source were experimentally demonstrated, and reaction models for gas phase excitation and surface excitation were proposed.
Abstract: Photoexcited chemical‐vapor deposition (CVD) and etching using synchrotron radiation as an exciting light source were experimentally demonstrated. CVD of silicon nitride film and etching of Si and SiO2 by SF6+O2 gases are described in detail. In several reaction systems, it was found that the surface photoexcitation was an important mechanism. Reaction models for gas‐phase excitation and surface excitation were proposed.
86 citations
TL;DR: In this article, the spectra of luminescence and photoexcitation as well as emission decay kinetics in various parts of spectra are investigated in ZnWO4 and CdWO 4 crystals in a wide temperature range (4.2 to 300 K).
Abstract: The spectra of luminescence and photoexcitation as well as emission decay kinetics in various parts of spectra are investigated in ZnWO4 and CdWO4 crystals in a wide temperature range (4.2 to 300 K). The bands of red afterglow and of rapidly decaying violet luminescence are observed for the first time. The likeness of the emission properties of ZnWO4 and CdWO4 allows the explanation of the luminescence in these tungstenite type crystals in terms of configurational coordinate diagrams of self-activated radiation centre and of self-trapped exciton.
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81 citations
TL;DR: In this paper, photoexcitation of D2S at 49-96 nm produces fluorescence with a quantum yield of about 5% and the emitters were identified from the fluorescence spectra to be D 2S+, SH+ and SD+ (A-X) transitions.
Abstract: Photoabsorption and fluorescence cross sections of H2S and D2S were measured in the 49–240 nm region using synchrotron radiation as a light source. Fluorescence from photoexcitation of H2S appears at 49–97 nm but not in the longer wavelength region. Fluorescence spectra were dispersed, and used to identify the emitters to be H2S+(A), SH+(A), and H(n>2). The fluorescence quantum yield is about 6%. Photoexcitation of D2S at 49–96 nm produces fluorescence with a quantum yield of about 5%. The emitters are identified from the fluorescence spectra to be D2S+(A), SD+(A), and D(n>2). The Franck–Condon factors for the SH+ and SD+ (A–X) transitions were determined. The SD(A–X) fluorescence was observed from photoexcitation of D2S at 100–151 nm, for which the fluorescence cross section and quantum yield were measured.
81 citations
TL;DR: In this paper, an improved time-resolved luminescence spectroscopy system using sum frequency generation was reported, which has the following attributes: high time resolution (<400 fs, currently limited by the laser), ability to determine absolute zero in time delay with high precision, wide spectral range, and large dynamic range.
Abstract: We report an improved time‐resolved luminescence spectroscopy system using sum frequency generation. The system has the following attributes: high time resolution (<400 fs, currently limited by the laser), ability to determine absolute zero in time delay with high precision, wide spectral range, and large dynamic range which allows measurement of luminescence under weak photoexcitation. We illustrate these with examples of time‐resolved luminescence spectra from GaAs.
67 citations
TL;DR: In this article, photoinduced and doping-induced absorption spectra of poly(3-methylthienylene) (P3MT) in the infrared-frequency range were analyzed.
Abstract: We report detailed photoinduced and doping-induced absorption spectra of poly(3-methylthienylene) (P3MT) in the infrared-frequency range. The four infrared-active translational (T) modes of bipolarons and the weak-ring (R) modes associated with the ring deformation were observed, as in polythiophene (PT). Detailed analysis based on the amplitude-mode formalism shows that the nondegenerate ground state leads to an ``extrinsic'' contribution to the energy gap of 0.26 eV in P3MT, and that the pinning is weaker than in PT.
58 citations
TL;DR: In this article, the spectral dependence of the optical absorption and its temperature derivative is different for the two polarisations, and there is evidence that the long-lived photoexcited charge states that give rise to PA and photoconductivity are preferentially excited with E polarised perpendicular to the chains.
51 citations
TL;DR: In this article, the formation and decay of a triplet state in a polydiacetylene single crystal after photoexcitation at 337 nm was observed directly by pulsed ESR.
51 citations
TL;DR: In this article, an experimental observation of a blue shift in the n=1 heavy-hole exciton line of In0.53Ga0.47As/InP multiple quantum wells resulting from a picosecond photoexcitation in the transparent spectral region was reported.
Abstract: We report an experimental observation of a blue shift in the n=1 heavy‐hole exciton line of In0.53Ga0.47As/InP multiple quantum wells resulting from a picosecond photoexcitation in the transparent spectral region. The temporal response of this shift follows the excitation and it is attributed to the optical Stark effect. The shift was measured to be 0.19 meV for an incident light with a photon energy 20 meV below the exciton peak and with a 10‐MW/cm2 intensity.
TL;DR: In this article, the authors have made detailed time-resolved transient absorption spectral measurements and timeresolved fluorescence measurements upon the pyrene-pyromellitic dianhydride (PMDA) system in various solvents with picosecond laser spectroscopy.
Abstract: In order to elucidate the underlying mechanisms showing that no dissociated ion radicals are produced even in acetonitrile solution when some complexes of the strong electron donors and acceptors with CT absorption bands in the visible region are photoexcited, the authors have made detailed time-resolved transient absorption spectral measurements and time-resolved fluorescence measurements upon the pyrene-pyromellitic dianhydride (PMDA) system in various solvents with picosecond laser spectroscopy A weakly fluorescent electron-transfer (ET) state with 400-ps lifetime is formed by photoexcitation in benzene solution, while nonfluorescent geminate ion pairs with much shorter lifetimes due to the charge recombination (CR) deactivation are formed in more polar solvents In all solutions examined, dissociation into free ions from the geminate pair cannot compete with the CR deactivation which becomes faster in more polar solvents due to the decrease of the energy gap between the ion pair and neutral ground state Moreover, it has been demonstrated that ion pairs produced by encounter between excited pyrene and unexcited PMDA in acetonitrile have more loose structure and show a smaller CR rate constant than those produced by exciting the ground-state complex
TL;DR: In this article, the authors reported a detailed assignment of photoexcitation and partial-channel photoionization processes in the valence shell of H 2 S employing single-and coupled-channel, vertical-electronic, static-exchange approximations.
TL;DR: In this article, photoabsorption and fluorescence cross sections of SiF4 were measured in the 49-120 nm region using synchrotron radiation as a light source, and the fluorescence was dispersed to identify the emitting species.
Abstract: The photoabsorption and fluorescence cross sections of SiF4 were measured in the 49–120 nm region using synchrotron radiation as a light source. Absorption bands were tentatively assigned to Rydberg states and their oscillator strengths were determined. The fluorescence was dispersed to identify the emitting species. In the 49–58 nm region, the emitter is attributed to the excited SiF+4 (D) ion. In the 92–98 nm region, the fluorescence is likely produced by the excited SiF*3 radical. Photodissociation process of SiF4 in the extreme ultraviolet region is discussed.
TL;DR: These Be-like uv lasers pumped by resonant photoexcitation are prototypes for soft x-ray lasers in higher-Z, isoelectronic analogs.
Abstract: Multiple-pass gain is reported at 2177 and 2163 A\r{} in C iii ions in a vacuum-arc discharge, pumped by Mn vi line radiation from a laser-produced Mn plasma. These Be-like uv lasers pumped by resonant photoexcitation are prototypes for soft x-ray lasers in higher-Z, isoelectronic analogs.
TL;DR: In this article, the ESR spin density and linewidth in polythiophene films decrease upon illumination of an infrared light, and the photocurrent response is observed at the infrared region too.
TL;DR: In the range 110-200 nm the absorption features of Si2Cl6 closely resemble those of SiCl4 and the peaks observed are tentatively assigned to the Rydberg transitions of a Cl lone-pair electron.
TL;DR: In this article, the photoexcited triplet state of free-base porphycene and its tetra-n-propyl derivatives, oriented in a uniaxial liquid crystal, was investigated by laser photoexcitation -EPR diode detection.
Abstract: The photoexcited triplet state of free-base porphycene and its tetra-n-propyl derivatives, oriented in a uniaxial liquid crystal, was investigated by laser photoexcitation - EPR diode detection. By monitoring the transient behavior of the magnetization, time-dependent CW spectra were obtained and examined. The results yield (a) positive values for the zero-field splitting parameters D; (b) the location of the fine structure tensor axes in the molecular frame (x and y lie in-plane and cross the bridges between the pyrrole rings, and z is perpendicular to the porphycene plane.
TL;DR: In this paper, a photoexcitation of 1,3-bis(1-naphthyl)-2-propanone in the carbonyl or naphthalene chromophore leads to the formation of a carbonyls-localized singlet state in the subnanosecond time scale.
Abstract: Photoexcitation of 1,3-bis(1-naphthyl)-2-propanone in the carbonyl or naphthalene chromophore leads to the formation of a carbonyl-localized singlet state in the subnanosecond time scale. This singlet decays (tau/sub s/ = 1.4 ns in isooctane), presumably to yield the carbonyl triplet, which rapidly populates the naphthalene-localized triplet state. This intermediate can be readily detected by laser flash photolysis and shows typical naphthalene-like characteristics (TT absorption, lambda/sub max/ = 430 nm). Product and quenching studies indicate that the Norrish Type I cleavage occurs from the singlet state with Phi approx. = 0.002. Excitation of the triplet state with the pulses from a dye laser (430 nm) leads to cleavage of the CH/sub 2/-CO bond to yield 1-naphthylmethyl radicals in a process that the authors describe as a reluctant Norrish Type I reaction. The quantum yield for this process is approx.0.06. The structural features required for this type of process to occur are discussed.
TL;DR: In this article, the authors studied the energy relaxation of hot carriers in GaAs/GaAs0.5P 0.5 strained-layer superlattices following photoexcitation.
Abstract: We have studied the energy relaxation of hot carriers in GaAs/GaAs0.5P0.5 strained‐layer superlattices following picosecond photoexcitation. A significant enhancement of highly excited carrier distribution lifetimes over those of bulk GaAs was observed at cryogenic as well as room temperatures. These results support the explanation of photocurrent results reported for solar photoelectrodes made with these structures. Comparison results were also obtained for a GaAs/AlGaAs multiple quantum well structure which showed even longer hot‐carrier lifetimes.
TL;DR: In this article, room temperature laser excitation of benzophenone triplets in their visible absorption band in benzene solvent leads to their deactivation with concomitant ground state repopulation.
TL;DR: In this paper, the photodissociation cross section for production of specific NO quantum states is found to be structured in the photolysis wavelength, which is assigned to intermediate resonance in the two-photon photolyysis.
Abstract: Quantum states of NO2 are selected and then photodissociated by resonant two‐photon photoexcitation. The total photolysis energy is scanned over a region from 50 cm−1 below to 300 cm−1 above the threshold for production of NO(X 2Π)+O(1D). This channel yielding excited oxygen is observed to dominate the production of vibrational ground state NO. Diatomic product J and Λ doublet state distributions are probed by resonant two‐photon ionization. The photodissociation cross section for production of specific NO quantum states is found to be structured in the photolysis wavelength. This structure is assigned to intermediate resonance in the two‐photon photolysis. Rotational structure is identified in this pattern, and confirmed by separate optical–UV–double resonance spectroscopy using the same intermediate states in combination with levels of the 3pσ 2Σ+u Rydberg state of NO2. Though photodissociation dynamics are found to be a very sensitive function of photolysis wavelength, different wavelengths that promo...
TL;DR: In this article, the performance characteristics of InGaAs/GaAs strained-layer superlattice coplanar ridge-type directional couplers realized by molecular beam epitaxy are reported.
Abstract: The performance characteristics of InGaAs/GaAs strained-layer superlattice coplanar ridge-type directional couplers realized by molecular beam epitaxy are reported The measured power transfer characteristics with 115 micron incident photoexcitation demonstrate nonlinear coupling due to absorption associated with the tails of the excitonic resonances in the quantum wells From a theoretical fit of the measured data, the nonlinear refractive index coefficient, n2, of the multiquantum well is found to be 225 x 10 to the -7th sq cm/W This agrees very well with a value of n2 = 19 x 10 to the-7th sq cm/W obtained independently on the same material from interferometric measurents
TL;DR: In this paper, a large anisotropy of μ||/μ⊥ ≈ 50 has been found for carrier motion parallel and perpendicular to the chains, indicating interchain charge creation as predominant mechanism of the photoexcitation of carriers.
Abstract: Transient photoconductivity in highly oriented polyacetylene has been investigated. A large anisotropy of μ||/μ⊥ ≈ 50 has been found for carrier motion parallel and perpendicular to the chains. The relaxation has been followed over 8 orders of magnitude in time, establishing directly the existence of a fast (τ1/2 ≈ 100 ps) and a slow component (lasting up to seconds). An appreciable anisotropy has been observed with respect to the polarization of the incident light, indicating interchain charge creation as predominant mechanism of the photoexcitation of carriers.
TL;DR: In this paper, the time evolution of events connected to photoabsorption in adsorbate layers can be subdivided into primary (photoexcitation/ionization including multiple excitations and screening), secondary (Auger decay in the case of core excitations), and tertiary (bond-breaking) processes.
Abstract: The time evolution of events connected to photoabsorption in adsorbate layers can be subdivided into primary (photoexcitation/ionization including multiple excitations and screening), secondary (Auger decay in the case of core excitations), and tertiary (bond-breaking) processes. On all these stages, manybody interactions are important. Improved understanding can be gained, if all these processes are viewed together. For adsorbate core excitations on metal surfaces, these connections are examined in some detail, using recent data. Auger spectra for the decay of well-defined primary excitations show that essentially all higher primary excitations have decayed by the time Auger deexcitation occurs; an exception is briefly discussed. On the other hand, the strong influence of delocalization upon the probability of successful bond-breaking leads to an excessive amplification of surviving higher excitations in photodesorption, particularly of fragment ions. To somewhat lesser extent, this is also the case for primary valence excitations and for desorption of neutral and ionic molecules. It is concluded that competition–and possibly even interference–between many-body interactions (screening vs. Coulomb localization) determines this selective branching as seen in electron emission and in desorption.
TL;DR: In this paper, the authors measured polarization ratios for a range of expected ratios for the various isolated and mixed branches of the NO X2Π1/2→A 2Σ+ transition.
Abstract: Polarized two‐photon photodissociation of NO2 in the region of 480 nm yields NO(v‘=0) with an anisotropic distribution of J. Measured polarization ratios are compared to quantum mechanical calculations for a range of expected ratios for the various isolated and mixed branches of the NO X2Π1/2→A 2Σ+ transition. Theoretical results show that main branches and their respective satellites (e.g., R11 and R21 branches) have the same transition moment directionally, though their intensities are in general different, implying that care is needed in interpreting polarization data from the mixed branches, such as (Q21+R11) or (Q11+P21), which measure the Π+ and Π− Λ doublet, respectively. Recognition of this fact is particularly important for properly separating the consideration of electron density distributions of Λ doublets from transition moment directionalities, as this has been a source of confusion in the literature. The measured results indicate that the principal two‐photon photoexcitation pathway in NO2...
TL;DR: In this paper, photoabsorption cross sections and fluorescence excitation spectra of methanethiol vapor have been measured in the 130-200 nm wavelength region using synchrotron radiation.