Showing papers on "Photoexcitation published in 1982"
TL;DR: In this paper, the authors investigated the photochemical properties of n-type semiconductor electrodes (GaP, CdS, ZnO and TiO2) caused by the presence of oxidants.
53 citations
TL;DR: In this article, the onset of chaos in the electrical avalanche breakdown caused by weak photoexcitation at 4.2 K in n-GaAs has been described as the first example of a new type of phase transition in semiconductors.
Abstract: Periodic oscillations and turbulence in the electrical avalanche breakdown caused by the weak photoexcitation at 4.2 K in n-GaAs have been presented as a first example of the onset of chaos which originates in a new type of phase transition in semiconductors.
50 citations
TL;DR: In this article, a more careful treatment of the high excitation regime, where the subbands broaden into minibands, than earlier self-consistent calculations is presented, and the luminescence peak is found to shift with decreasing photoexcitation intensity far below the band gap of GaAs.
Abstract: Periodic multilayer structures of GaAs exhibit new semiconductor properties such as tunable effective band gap, long lifetime of photoexcited carriers, and quantization of carriers in space-charge-induced potential wells. We present a more careful treatment of the high excitation regime, where the subbands broaden into minibands, than earlier self-consistent calculations. Experimentally we have used photoluminescence and resonant in-elastic light scattering measurements to study the subband structure. The luminescence peak is found to shift with decreasing photoexcitation intensity far below the band gap of GaAs. By comparing the peak position with the theory we determine the carrier concentration. Resonant spin-flip single-particle excitations directly give the subband splittings which are in good agreement with the theoretical results. At high excitation intensities, the subbands merge and a quasi-three-dimensional behavior is found.
42 citations
TL;DR: An equation-of-motion procedure to study intramolecular vibrational relaxation in polyatomic molecules is developed and applied to study the transient structural response of a polyene to photoexcitation.
Abstract: An equation-of-motion procedure to study intramolecular vibrational relaxation in polyatomic molecules is developed and applied to study the transient structural response of a polyene to photoexcitation. The lattice response at short times (\ensuremath{\sim}20 fs) following excitation is characterized by an adiabatic relaxation which is highly specific to the exciting frequency. For longer times (20-1000 fs) this relaxation is strongly modified by the nonadiabatic relaxation of the excited carrier and takes the form of a "splash" in the bond-alternation profile, which reflects the transient distribution of the excited carrier in energy.
32 citations
TL;DR: In this paper, the absorption spectrum of methyl iodide has been photographed in the wavelength region 80-270 AA and a value of 1.72+or 0.05 eV has been deduced for the 4d32/-4d5/2 spin-orbit splitting in the iodine atom.
Abstract: The absorption spectrum of methyl iodide has been photographed in the wavelength region 80-270 AA. Photoexcitation of the iodine 4d subshell was found to dominate the spectrum, giving rise to discrete 1A1 to 1A1, 1E transitions and a giant 4d to epsilon f continuum resonance. An analysis of the transitions is given and a value of 1.72+or-0.05 eV deduced for the 4d32/-4d5/2 spin-orbit splitting in the iodine atom.
30 citations
TL;DR: In this paper, the angular distribution and spin polarization of Auger electrons following photoionization and photoexcitation are presented in concise parametrized expressions, which are similar to corresponding expressions for photoelectrons.
Abstract: Angular distribution and spin polarization of Auger electrons following photoionization and photoexcitation are presented in concise parametrized expressions. The striking similarity with corresponding expressions for photoelectrons enables one to apply kinematic properties known for photoelectrons in analyzing Auger electrons.
30 citations
TL;DR: In this paper, a theory of quasi-continuum phenomena in unimolecular photoreactions is proposed, which is simple enough not to require computer implementation but is able to reproduce analytically and semi-quantitatively the results of full computer simulations.
27 citations
TL;DR: In this paper, the average internal energies of photoexcited ions have been varied by changing the temperature of the source in which the ions are formed and photoexciting them through constant photoexcitation energies in the field-free region of a double focusing mass spectrometer.
25 citations
TL;DR: In this article, various aspects of the emission spectroscopic evidence for the existence of rotamers in trans-1,2-diarylethylenes are discussed.
22 citations
TL;DR: In this article, an approximate analytic theory of photoexcitation of a quasicontinuum is presented, which accounts for unimolecular dipole dephasing relaxation and partial dipole recorrelations.
Abstract: We present an approximate analytic theory of photoexcitation of a quasicontinuum. The theory accounts for unimolecular dipole dephasing relaxation and partial dipole recorrelations. It is based on systematic repeated interruption of coarse‐grained dynamical evolution of the system’s wave function. We predict sign reversals and discontinuities in transition rates, and other quasiperiodic phenomena. The theory gives fair agreement with computer simulations and reproduces features of two known exactly soluble models.
21 citations
TL;DR: In this article, it is shown in quantitative agreement with a theoretical model that the population of shallow acceptors, e.g. B and Al, which are present as impurities in concentrations of NB,Al≈1012-1014 cm−3 strongly affects the photoexcited hole concentration.
Abstract: Hall measurements at low temperaturesT<50 K have been performed on Si:In (NIn≈1017 cm−3) and Si:Ga (NGa≧1018 cm−3) with infrared photoexcitation of holes into the valence band. It is shown in quantitative agreement with a theoretical model that the population of shallow acceptors, e.g. B and Al, which are present as impurities in concentrations ofNB,Al≈1012-1014 cm−3 strongly affects the photoexcited hole concentration. Photo-Hall measurements can, therefore, serve as a tool for the determination of low impurity acceptor concentrations in the case of high In- or Ga-doping. Hole capture coefficientsBIn=6×10−4 (T/K)−1,8 cm3 s−1 andBGa=2×10−4 (T/K)−1 cm3 s−1 have been determined.
TL;DR: In this article, a two-photon photoexcitation of SO2 at 248 nm is found to lead to a number of primary fragments including S(3P) and SO(X 3Σ−).
Abstract: Sequential two‐photon photoexcitation of SO2 at 248 nm is found to lead to a number of primary fragments including S(3P) and SO(X 3Σ−). Further excitation of some of these photoproducts was also observed, occurring by both linear and two‐quantum mechanisms. The resulting molecular X←B (v\,2) ultraviolet fluorescence from SO and the atomic 3P←3S vacuum ultraviolet emission from S atoms were detected and an analysis of the energy flow patterns was made.
TL;DR: The photo-Hall effect in a new type of periodic p-n doping multilayer structures (superlattices) of GaAs grown by molecular beam epitaxy has been investigated in this article.
Abstract: The photo-Hall effect in a new type of periodicp-n doping multilayer structures (superlattices) of GaAs grown by molecular beam epitaxy has been investigated. In these space charge systems electrons and holes are separated in real space. As a consequence, large deviations from thermal equilibrium become quasi-stable. Carrier generation by optical absorption occurs in these doping superlattices even at photon energies far below the gap of the homogeneous semiconductor material. The photoexcitation results in a strong enhancement of the conductivityparallel to the layers and in a substantial photovoltaic response. An increase in carrierconcentration as well as an increase in carriermobility both contribute to the observed enhancement of the conductivity under excitation. The absolute values of changes in free-carrier concentration are very large due to the manyfold active layers of the structure. The measured free-carrier mobilities depend on the population of the multilayer system. A reduction in mobility as compared to bulk material is found to be more pronounced in weakly populated systems. This finding is caused by the larger weight of the boundary regions of the total active layers where the free-carrier density is lower than the density of ionized impurities resulting in an enhanced impurity scattering.
TL;DR: In this article, the formation of superdense electron-hole plasma in CuCl was reported for injected carrier densities n > 10 20 cm -3, and the plasma lifetime was determined to be τ ≲ 10 −11 s.
TL;DR: In this paper, a series of spin resonance experiments on samples illuminated with light at photon energies was conducted and the results set an upper limit on the quantum efficiency for photoproduction of unpaired spins, γs⩽ 2×10-7, implying that the photo-induced excited states and the photo generated carriers are spinless and are associated with charged solitons.
TL;DR: In this article, the properties of CH3I+− and CD3I− ions have been studied using a mass spectrometer having facilities for collisional excitation and photoexcitation of mass-selected ions.
TL;DR: In this paper, the electronic structure and intersystem crossing at excited states of the relaxed exciton, (V k e ) A, perturbed by monovalent cation impurity in KCl and KBr have been studied by pulsed laser irradiation of samples populated with the lowest triplet ( V k e ), A.
Abstract: The electronic structure and intersystem crossing at excited states of the relaxed exciton, ( V k e ) A , perturbed by monovalent cation impurity in KCl and KBr have been studied by pulsed laser irradiation of samples populated with the lowest triplet ( V k e ) A . It is found that the σ-polarized luminescence, at 3.03 eV and 2.93 eV in KCI:Na and KBr:Na, respectively, that decays in less than 10 ns is produced upon the photoexcitation of the lowest triplet ( V k e ) A . The fast luminescence is ascribed to the fluorescence (referred to as 1 -luminescence) from the lowest singlet ( V k e ) A . The degree of polarization of the optical absorption due to the lowest triplet ( V k e ) A is determined and it is shown that the electron orbitals of ( V k e ) A are in the order of b 2 u , b 3 u , b 1 u and b * 3 u from lower energy. The S 1 luminescence is found to be produced most efficiently by the electron excitation from the a g orbital to the b * 3 u orbital.
01 Dec 1982
TL;DR: In this paper, the photoexcitation dynamics of CO 2 -laser-excited SF 6 in a molecular free-expansion jet were investigated using simulated Raman spectroscopy.
Abstract: Stimulated Raman spectroscopy is used to probe the photoexcitation dynamics of CO 2 -laser-excited SF 6 in a molecular free-expansion jet. Time-dependent depletion of rotational levels in the ground state is observed by monitoring the ν 1 Raman spectrum at various delay times after the CO 2 -laser excitation pulse. Optical Stark shifts are also seen, at short delay times, arising from resonances of the IR laser pulse with ν 3 transitions from both ground and ν 1 = 1 states. Molecules excited to the ν 3 = 1 level are detected by scanning the ν 1 + ν 3 − ν 3 hot band. A direct determination of the anharmonicity X 13 = −2.910 ± 0.002 cm −1 is thus obtained.
TL;DR: In this paper, the authors proposed a model based on photoexcitation of the electrons at defect-related energy levels above the Fermi level, and the thermal excitation of lower-energy electrons to the empty defect related levels.
Abstract: When photoillumination is interrupted, the exoelectron emission from scratched metal samples decays quickly; when the illumination is resumed, however, the recovered exoelectron emission shoots up to a value significantly higher than before and then decreases gradually–a fact overlooked by previous researchers. This transient phenomenon has been studied in some detail as a function of the interval of the interruption and photon energy. To explain our data we propose a model, according to which there are two excitation processes competing during PSEE; one is the photoexcitation of the electrons at defect-related energy levels above the Fermi level, and the other is the thermal excitation of lower-energy electrons to the empty defect-related levels. Rate equations based on this model were found to be in satisfactory agreement with our observations.
TL;DR: In this article, a detailed calculation of solar O III EUV line intensities is described, including the process of photoexcitation by He II Lyman-cap alpha, which is found to be in agreement with observed intensities.
Abstract: A detailed calculation of solar O III EUV line intensities is described, including the process of photoexcitation by He II Lyman-..cap alpha... Excellent agreement with observed intensities is found for a photoexciting radiation field of intensity 9.8 x 10/sup -8/ ergs cm/sup -2/ s/sup -1/ sr/sup -1/ per Hz. The presence of some O III lines in flares is discussed. The process of charge exchange does not appear to be a significant factor in formation of the O III spectrum.
TL;DR: In this paper, the Tchebycheff imaging technique and the separated-channel static exchange approximations are used to calculate the variation with photon energy of the partial cross sections to the ionic states of NO arising from 4 sigma, 5 sigma, 1 pi and 2 pi ionisation.
Abstract: Calculations of the variation with photon energy of the partial cross sections to the ionic states of NO arising from 4 sigma , 5 sigma , 1 pi and 2 pi ionisation are described. The Tchebycheff imaging technique and the separated-channel static-exchange approximations are used. The results are compared with experimental data from (e,2e) spectroscopy and from synchrotron radiation.
TL;DR: In this paper, the authors demonstrated the production of molecular Rydberg state in K2 by means of two-step photoexcitation with help of thermionic detection in a disc-shaped heatpipe oven.
Abstract: The authors have demonstrated the production of molecular Rydberg state in K2 by means of two-step photoexcitation with help of thermionic detection in a disc-shaped heat-pipe oven. Preliminary results concern a spectroscopic investigation of the very high 'Rydberg region'. Results of the pressure shift of Rydberg lines are also presented.
TL;DR: In this article, it was shown that there appears to be no direct correlation between the cathodoluminescence and the absorption band at 220 nm (5.7 eV) in deformed MgO single crystals with different geometries.
Abstract: Optical absorption at 220 nm (5.7 eV) and cathodoluminescence emission at 410 nm (3.0 eV) have been measured in deformed MgO single crystals with different geometries. Whereas previous studies indicate that a luminescence band at 430 nm (2.9 eV) is due to photoexcitation of the absorption band at 220 nm, there appears to be no direct correlation between the cathodoluminescence and the absorption band.
TL;DR: In this article, a time-resolved far-infrared cyclotron resonance was carried out at liquid helium temperatures for both n- and p-type InSb under intrinsic photoexcitation.
Abstract: Time-resolved far-infrared cyclotron resonance was carried out at liquid helium temperatures for both n- and p-type InSb under intrinsic photoexcitation. The optically hot nature shows up very clearly for the photoelectron system. Detailed electron temperature analysis was carried out on a p-type sample, using the intensity ratio of the two lowest cyclotron transition signals. The electron temperature was found to decrease from 40 K at a time constant of 6.5 µs. Joint observation of electron and hole signals at four different wavelengths enabled us, using the calculation by Pidgeon and Brown, to modify the values of the Luttinger parameters of the valence band. Cyclotron emission similar to that detected under electrical excitation was observed in an n-type sample.
TL;DR: In this paper, the authors observed the generation of nonthermal, large amplitude acoustic surface waves at GHz frequencies on the surface of a GaAs crystal under intense illumination with 514.5 nm radiation from an Ar+ laser at room temperature.
Abstract: In the experiments reported here we observed the generation of non-thermal, large amplitude acoustic surface waves at GHz frequencies on the surface of a GaAs crystal under intense illumination with 514.5 nm radiation from an Ar+ laser at room temperature. The acoustic surface waves were detected by optical Brillouin spectroscopy.
TL;DR: In this article, the angular distribution and polarization of coherent fluorescence radiation following photoexcitation and photoionization including all multipole transitions are parametrized, and their implications are discussed.
Abstract: We present concise parametrized expressions for the angular distribution and polarization of the coherent fluorescence radiation following photoexcitation and photoionization including all multipole transitions. Many interesting cases are discussed, and their implications are pointed out.
TL;DR: In this article, the authors considered the effect of mixing normal modes at electronic transition on the behaviour of mean value of configurational coordinate and its fluctuation characteristics, and derived formulas relating the relaxation characteristics with the dynamical Green's function.
TL;DR: In this article, the absorption, photoluminescence, and x-ray luminescence spectra of pure and neodymium-activated YAG crystals grown by the horizontal directional crystallization method were investigated at 295°K in the wavelength range 190-900 nm.
Abstract: The absorption, photoluminescence, and x-ray luminescence spectra of pure and neodymium-activated YAG crystals grown by the horizontal directional crystallization method were investigated at 295°K in the wavelength range 190–900 nm. A particular study was made of wide strong absorption bands with maxima at 224 and 205 nm due to introduction of neodymium into YAG crystals. These bands were attributed to the 4f →5d transitions in Nd3+ ions localized at normal and anomalous structural positions. A system of luminescence bands observed in the 260–620 nm range excited by x-ray and hard (e >4.79 eV) photoexcitation of YAG:Nd was attributed to transitions from the 2F 25/2 (e =37 850 cm−1) level to levels of all the lower neodymium multiplets. In the case of excitation by softer photons (3.22 ≲ e ≲ 4.68 eV), the luminescence spectrum was due to transitions from another metastable level 2P3/2 (e =25 990 cm−1) to levels of lower terms. A new structural scheme was proposed for the formation of anomalous rare-earth ion centers in laser garnets.
TL;DR: In this article, the minority carrier lifetime in a conventional N+/P silicon photocell has been investigated experimentally, and the recombination processes can be described by (i) a positive field controlled Auger recombination at low photo injection level, (ii) positive field influenced Auger injected at medium injection level and (iii) a negative field controlling Auger injection at high injection level.
Abstract: The minority carrier lifetime in a phosphorous‐diffused layer of a conventional N+/P silicon photocell has been investigated experimentally. The photovoltages have been measured as a function of photon flux density from low to medium illumination levels. From the quasi‐Fermi level analysis of Gray‐Kao‐Schroder, we have determined the carrier recombination lifetime as a function of the photogeneration rate 〈G〉 in the heavily‐doped N+ layer. When the band gap narrowing effect is taken into consideration, the recombination processes can be described by (i) a ’’positive‐field controlled’’ Shockley‐Reed‐Hall recombination at low photo injection level, (ii) a ’’positive‐field influenced’’ Auger recombination at the medium injection level, and (iii) a ’’negative‐field controlled’’ Auger recombination at the high injection level. Under a very high photoexcitation condition, the magnitude of the saturated open circuit voltage of the cell is limited by the recombination lifetime at the surface contact region.
TL;DR: In this paper, the energy distribution function for hot photo-excited electrons in GaAs is studied by means of numerical calculations, which are appropriate to conditions of continuous monochromatic photoexcitation and lattice temperatures in the liquid helium range.
Abstract: The energy distribution function for hot photoexcited electrons in GaAs is studied by means of numerical calculations. The calculations are appropriate to conditions of continuous monochromatic photoexcitation and lattice temperatures in the liquid helium range. A Boltzmann equation approach is used to take account of the following effects: injection of electrons into the conduction band (at an energy below the threshold for LO phonon emission), collisions between electrons of unlike spin, collisions between electrons of like spin, scattering of electrons by acoustic phonons via the piezoelectric and deformation potential interactions and departure of electrons from the band via recombination. The Boltzmann equation is solved numerically by using an iterative technique. The numerical results are used to show how the distribution functions are characteristic of the scattering events undergone by the photoexcited electrons. The results also lead to quantitative estimates of the range of electron densities in which the electrons have a quasi-equilibrium distribution and the range of electron densities in which the electron distribution does not have a quasi-equilibrium form.