Showing papers on "Exciton published in 1980"
242 citations
TL;DR: In this paper, the first observation of sharp photoluminescence lines with energies less than the energy of the recombination peak associated with the exciton bound to the neutral carbon acceptor in nominally undoped p-type GaAs grown by molecular beam epitaxy (MBE) is reported.
Abstract: The first observation of several sharp photoluminescence lines with energies less than the energy of the recombination peak associated with the exciton bound to the neutral carbon acceptor in nominally undoped p‐type GaAs grown by molecular beam epitaxy (MBE) is reported. The lines ranging from 1.5110 to 1.5040 eV are interpreted as radiative recombination of defect‐induced bound excitons directly correlated with the interaction of As4 molecular beam species during MBE growth. These lines disappear totally when As2 instead of As4 beams are used. We then demonstrate that all sharp photoluminescence features, previously only detected in the best LPE samples, are now also observed in thin MBE GaAs layers when grown from As2 beam species.
206 citations
TL;DR: In this paper, the Levine-Mark theory of the surface states of ionic insulators was tested for oxides, and the numerical values of the parameters appropriate to the oxides were evaluated by using experimental data on bulk excitons.
Abstract: Ultra-violet (u.v.) diffuse reflectance spectra of microcrystalline MgO, CaO, SrO and BaO reveal bands at energies below those of bulk excitonic transitions. Correlation of the spectra permit three distinctive absorptions (I, II, III) to be identified, each with similar characteristics in the respective oxides. The absorptions are ascribed to surface states, and the transitions have the characteristics of excitons. Excitons II and III obey the Mollwo–Ivey relation typical of bound excitons, but excition I with the highest energy of transition behaves similarly to a free exciton of the bulk. The four oxides are isostructural and ionic. The Levine–Mark theory of the surface states of ionic insulators, not hitherto tested for oxides, is examined. The numerical values of the parameters appropriate to the oxides are evaluated by using experimental data on bulk excitons. It is shown that the theory accounts satisfactorily for the energies of exciton I in MgO, CaO and SrO on the basis that it is an exci...
136 citations
TL;DR: In this paper, the resonance Raman scattering by multiple-LO phonons has been studied in the E'1 exciton region of the layer compound InSe and the nature of the electron-lo phonon interaction in InSe is discussed in terms of the polaron coupling constants.
104 citations
TL;DR: In this paper, a free-exciton gas is studied as a function of generated particle density in O at 1.5 K. A line-shape analysis of the subsequent recombination shows a gradual evolution, from a classical regime at low density, to a highly quantum-statistical one with chemical potential.
Abstract: A free-exciton gas is studied as a function of generated particle density in ${\mathrm{Cu}}_{2}$O at 1.5 K. A line-shape analysis of the subsequent recombination shows a gradual evolution, from a classical regime at low density, to a highly quantum-statistical one with chemical potential $\ensuremath{\mu}\ensuremath{\simeq}0$.
102 citations
TL;DR: The energy of an electron-hole pair in anthracene is calculated for a complete range of separations and the resulting change-transfer exciton potentials are used to analyze optical charge carrier generation as a function of wavelength and temperature as discussed by the authors.
93 citations
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TL;DR: In this paper, the photovoltaic and photoconductivity effects in polyacetylene were investigated and the spectral range was extended to include the visible region as well as the visible spectrum.
92 citations
TL;DR: In this paper, the Raman lineshape of the A g exciton level of the 766 cm −1 vibrational mode of naphthalene at 1.5 K was investigated.
80 citations
TL;DR: In this paper, the A1 exciton line is accompanied by an oscillatory structure with constant intervals of 356 cm-1 due to indirect hot exciton creation, which indicates that the hole-binding nature of the Mn center can bind a free exciton.
Abstract: Single-ion luminescence due to Mn2+ and donor-acceptor pair luminescence due to (Cu, Al), (Ag, Al) and (Au, Al) centered in hexagonal ZnS have been investigated at 75 K with a major focus on exciton structures in the excitation spectra. Appearance of exciton peaks in Mn2+ luminescence excitation spectra indicates that the isoelectronic Mn center can bind a free exciton. Such an exciton binding is caused by the hole-binding nature of the Mn center. The A1 exciton line is accompanied by an oscillatory structure with constant intervals of 356 cm-1 due to indirect hot exciton creation. Exciton structure in the DA pair excitation spectra varies from ambiguous to distinctive dips with increasing monitored wavelength. Distant DA pairs do not bind free excitons, but close pairs can do so.
78 citations
TL;DR: In this paper, a transition mechanism of the room-temperature blue emission band of ZnSe was investigated in order to elucidate the transition between the photoluminescence of low-resistivity and the electroluminecence of the znSe diodes of metal-insulator-semiconductor (MIS) structures.
Abstract: The near‐band‐edge photoluminescence of ZnSe crystals grown from an In solution has been studied in order to elucidate a transition mechanism of the room‐temperature blue emission band which is typically observed in the photoluminescence of the low‐resistivity ZnSe crystals and the electroluminescence of the ZnSe diodes of metal‐insulator‐semiconductor (MIS) structure. On the basis of the temperature‐dependent behavior of the various near‐band‐edge emission bands, i.e., changes in the peak energies and the intensities over the wide temperature range, the room‐temperature blue emission is attributed to the recombination between free holes and donor electrons. Special attention is paid to a relation between this emission and the low‐temperature exciton emission due to the recombination of excitons bound to the ionized donor.
74 citations
TL;DR: In this paper, a quantitative fit with the Elliott's model is given for the position and intensity of the levels, which does not necessitate any variation of the apparent oscillator strength with thickness (or temperature).
Abstract: Optical constants (absorption coefficient and refractive index) of unstrained GaSe samples at low temperature have been measured in the vicinity of the band-edge and exciton series. A quantitative fit with Elliott's model is given for the position and intensity of the levels. This does not necessitate any variation of the apparent oscillator strength with thickness (or temperature). Parameters of the tridimensional hydrogenic series obtained from this fit give values of the band gap, the exciton binding energy, the damping of the excited levels, the oscillator strength of the transition, and the reduced effective masses of the exciton.
TL;DR: In this article, the resonance luminescence due to radiative annihilation of free excitons in Pyrene has been observed, and a thermal equilibrium is established between free and excimer states.
Abstract: The resonance luminescence due to radiative annihilation of free excitons in Pyrene has been observed. The luminescence band is located at 376 nm (F) at room temperature and is quite distinctive from so-called excimer luminescence band located at 450 nm. There is a potential barrier between the free exciton state and the excimer state which is located 540 cm -1 (66 meV) lower in energy with respect to the free exciton state. The luminescence decays exponentially with a life time of 180 nsec for both free excitons and excimers at 282 K. Discussion is given to explain free exciton creation and luminescence processes in terms of thermal equilibrium established between free excitons and excimers. The excimer is recognized as the self trapped exciton.
TL;DR: In this paper, local and global stabilities of an electron in deformable lattice with dimensionality δ and force range index λ are studied within the adiabatic approximation.
Abstract: Local and global stabilities of an electron in deformable lattice with dimensionality δ and force range index λ are studied within the adiabatic approximation. Depending on the sign of the stability index: σ=δ-2λ-2, one finds the free state to be locally stable (σ>0) ith discontinuous transition to globally stable self-trapped state beyond a critical value of coupling constant g , to be marginal (σ=0) with local (as well as global) stability being governed by g , or to be locally instabilized (σ <0) towards the optimum lattice distortion which grows continuously from zero with increasing g . A phase diagram is presented for an electron interacting simultaneously with two types of phonon fields with \(\sigma \lessgtr 0\). The potential barrier for self-trapping of a Wannier exciton is studied with particular attention to the effect of its internal motion, and is compared with the observation.
TL;DR: In this article, the authors reported a new photoluminescence (PL) band in indirect $X$-point phonon sidebands and an asymmetric shape with an abrupt high-energy cutoff.
Abstract: This paper reports a new photoluminescence (PL) band in indirect $\mathrm{Ga}{\mathrm{As}}_{1\ensuremath{-}x}{\mathrm{P}}_{x}$ that lies between donor-bound and free exciton PL peaks. It has relatively strong $X$-point phonon sidebands and an asymmetric shape with an abrupt high-energy cutoff. The lifetime varies rapidly over the PL linewidth. Properties of excitons in fluctuating random-alloy potentials are discussed. It is suggested that this line is due to excitons trapped by such potentials.
TL;DR: In this paper, simultaneous excitation of two dye laser beams is studied in which the intermediate state is the excitonic molecule and the final states are the longitudinal and transverse excitons.
TL;DR: In this paper, the second quantized boson theory was used to calculate the energies and oscillator strengths of the Coulomb transfer interactions in crystalline naphthalene, anthracene, tetracene and pentacene.
TL;DR: In this article, the resonance Raman profiles were measured for a perylene crystal exciton state (Au) corresponding to the 0-0 transition of the molecular 1B2u(S1) state.
Abstract: The resonance Raman profiles were measured for a perylene crystal exciton state (Au) corresponding to the 0–0 transition of the molecular 1B2u(S1) state. At both 77 and 4.2 °K the profiles of these extremely thin crystals do not coincide with the absorption spectra. This effect is frequency dependent damping perhaps caused by exciton–phonon interactions. The efficiency of resonant scattering relative to excimer emission is used to measure an exciton dephasing time of 6.4×10−14 sec. The luminescence of the population resulting from this loss of coherence was not observed suggesting that these excitons disappear within 5×10−13 sec.
TL;DR: In this article, the authors observed that the exciton lifetime in high purity silicon is strongly temperature dependent and proposed a theory that includes capture, evaporation, and recombination of excitons at neutral impurities.
Abstract: We observe that the exciton lifetime in high‐purity silicon is strongly temperature dependent. To describe our data we propose a theory that includes capture, evaporation, and recombination of excitons at neutral impurities. We suggest applications of exciton‐decay measurements to the determination of impurity content, capture cross sections, and electron‐hole droplet nucleation kinetics.
TL;DR: A broad charge transfer band is observed in the photoluminescence excitation (PLE) spectrum of the 2.5 μ Ni2+ luminescence in ZnSe : Ni.
TL;DR: In this article, the amplitude decay due to the presence of disorder is calculated through the time-dependent exciton Greens function, and the functional form of the decay is investigated, and different methods for its calculation are compared.
Abstract: Coherent states in molecular crystals are described as minimum‐uncertainty superpositions of all the crystal states that can interact with light, and their amplitude decay due to the presence of disorder is calculated through the time‐dependent exciton Greens function. The functional form of the decay is investigated, and different methods for its calculation are compared. The decay obtainable for the k=0 vibrational exciton in α‐N2 through direct time‐domain approximations provides good agreement with experimental results.
TL;DR: In this article, the absorption spectrum of E′1 and E1 exciton transitions in 3R(γ)-InSe has been measured at 1.8 K. Their photon energies, oscillator strengths and polarization dependences are fully explained in terms of Hopfield's quasicubic model.
TL;DR: In this article, a study of additional waves in the exciton region of CdS crystals is reported, showing a structure that is a direct reflection of the polariton dispersion law.
Abstract: A study of additional waves in the exciton region of CdS crystals is reported. Transmittivity and reflectivity of thin crystals is measured showing a structure due to the Fabry-Perot interference and the interference of additional waves. This structure is a direct reflection of the polariton dispersion law. Using the formulas for a spatially dispersive platelet and Pekar's additional boundary conditions the theoretical reflectivity curves are obtained numerically reproducing the essential experimental results. Values for all physical parameters defining dispersion and damping of the polaritons are found. Some evident deviations between the experimental curves and the present computer results for the reflectivity are pointed in connection with a discussion of the role of the surface exciton potential.
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TL;DR: In this paper, the excitation-level and impurity-concentration dependences of the luminescence-intensity ratio of bound exciton to free exciton have been investigated in detail so as to characterize the content of dopant impurities in silicon.
Abstract: The low-temperature exciton luminescence of silicon has been measured and analyzed on the basis of rate equations describing the formation and decay kinetics of free exciton, bound exciton and bound multiexciton complexes. In particular, the excitation-level and impurity-concentration dependences of the luminescence-intensity ratio of bound exciton to free exciton have been investigated in detail so as to characterize the content of dopant impurities in silicon. Analysis of experimental data for boron-doped silicon has shown that the dopant-impurity concentration and the compensation ratio by phosphorus donors can be quantitatively estimated from the exciton-luminescence data. These results suggest that analysis of exciton luminescence is a promising technique in silicon crystal characterization.
TL;DR: In this paper, the spatial dispersion of the excitonic molecule has been studied by the excitation into states of large wave vectors using two dye laser beams, and the relation between ω 1 and ω 2 is expressed by a straight line of slope 0.57.
Abstract: By the use of two dye lasers, the spatial dispersion of the excitonic molecule has been studied by the excitation into states of large wave vectors. With the first laser beam ω 1 ( k 1 ) an excitonic polariton is created at a large wave vector and an excitonic molecule is formed with the second laser beam ω 2 ( k 2 ). The relation between ω 1 and ω 2 is expressed by a straight line of slope 0.57, and the mass of the excitonic molecule is determined to be 2.3 times as much as that of the transverse exciton. In the two different configurations in which the two laser beams are in the same and opposite directions, excitonic molecules are created at k 1 ± k 2 . From the analysis of the relation between ω 1 and ω 2 in the two configurations, the excitonic mass is deduced to be (2.5∼3.0) m 0 .
TL;DR: In this paper, the authors used the Monte Carlo simulation method to simulate the diffusion of excitons in a cubic lattice with a Gaussian distribution of site energies (half width σ).
TL;DR: In this paper, the anomalies are due to the virtual formation of biexcitons in high intensity excitonic polariton-polariton scattering experiments, and the results are in quantitative agreement with the experimental observations of Itoh et al. for CuCl.
Abstract: We investigate in the framework of the dielectric formalism the anomalies which have been observed in high intensity excitonic polariton-polariton scattering experiments. The anomalies are due to the virtual formation of biexcitons. Our results are in quantitative agreement with the experimental observations of Itoh et al. for CuCl.
TL;DR: In this paper, the saturation effects of Eu3+ luminescence in Y2O2S were investigated using a pulsed nitrogen laser at room temperature and at 80 K, and also under pulsed cathode-ray excitation under room temperature.
Abstract: The saturation effects of Eu3+ luminescence in Y2O2S have been investigated using a pulsed nitrogen laser at room temperature and at 80 K, and also under pulsed cathode-ray excitation at room temperature. Interaction between excited-state Eu3+ ions gives rise to a predominant energy-loss mechanism causing saturation. One of the two Eu3+ ions in the charge transfer state (CTS) is forced to relax nonradiatively to the 7F state by dipole-dipole interaction, and the other is promoted to a higher bound exciton state, or eventually dissociated to a free hole and a bound electron. Interaction between a Eu3+ ion in the 5D state and a CTS-Eu3+ ion also causes nonradiative relaxation of the 5D state, which causes differences in the saturation behavior of different emitting states and brings about excitation intensity dependence in the luminescence decay curves.
TL;DR: In this paper, the authors measured the nonthermal distribution and subsequent evolution towards equilibrium by spin-echo spectroscopy of one of the triplet exciton zero-field transitions using a single crystal of 1.2.4,5tetra-chlorobenzene.