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1.
Pico-second time-resolved spectra of the spontaneous luminescence from high density electron-hole plasma in CdS are measured at 4.2 K suppressing the stimulation effect. It is found that after the pulse excitation hot carriers are cooled rapidly for the first 100 psec, and that therafter up to the 400 psec delay time the shape of spectra hardly changes but the spectral width depends on excitation density. Although it seems as if some kind of state like electron-hole liquid is formed, one cannot easily regard that state as the condensed electron-hole drop state. 相似文献
2.
S. A. Markov V. N. Makhov A. N. Vasil’ev V. Nagirnyi 《Bulletin of the Lebedev Physics Institute》2012,39(5):155-161
An analytical model for determining the spatial distribution of self-trapped excitons upon excitation at the Urbach absorption tail under conditions of absorption saturation is developed, and an expression for exciton luminescence decay kinetics in wide band-gap crystals was derived taking into account concentrational exciton self-quenching under such excitation conditions. 相似文献
3.
A new electronic resonant Raman effect in CdS is reported. Resonance enhancement at the I1 and I2 bound excitons is observed in differently doped (Cl, J, Li) samples. The energy, intensity dependency and Zeeman splitting suggest an electronic Raman effect associated with excited states of acceptor and donor bound excitons. 相似文献
4.
The nonlinear absorption of single picosecond light pulses (λ = 1.06 μm) in CdS is investigated at very high light intensities. Three-photon absorption and subsequent excited-state absorption of the generated electrons and holes explain the rapid decrease of transmission with increasing intensity. A three-photon absorption cross-section of σ(3) = (2±0.5) × 10-80 cm6 s2 and an average excited state absorption cross-section of σex = (7 ± 3) × 10-18 cm2 was determined. 相似文献
5.
S. A. Gavrilov V. V. Gusev V. S. Dneprovskii E. A. Zhukov A. N. Syrnikov I. V. Yaminskii E. A. Muljarov 《JETP Letters》1999,70(3):216-221
The characteristic features of the luminescence spectra of CdS semiconductor nanocrystals, crystallized in hollow channels
in a dielectric template, are explained in terms of excitonic transitions in semiconductor-insulator quantum wires. The excitonic
transition energies agree with the values calculated taking into account the effects of size quantization and the “dielectric
enhancement of excitons” — the large increase in the electron-hole attraction as a result of the difference between the permittivities
of the semiconductor and insulator. The theoretically computed binding energies of excitons in CdS quantum wires with a diameter
of 10 nm reach 170 meV. It is shown that the excitonic transition energy is constant for a wide range of wire diameters.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 3, 216–220 (10 August 1999) 相似文献
6.
We report on the first observation of 1s to 2p absorption by excitons in pure silicon. A group of strong lines at 10.2, 11.4 and 12.0 meV is observed along with a continuum extending to higher frequency. A theoretical model for the excitonic absorption accounts well for the observed structure. 相似文献
7.
The instability of the photocurrent in thin CDS films prepared by the electrohydrodynamic sputtering method is investigated. The degradation of photosensitivity of the films during prolonged illumination and the restoration of their photosensitivity in dark are explained by assuming the drift of ionized lattice defects in the field set up by negatively charged oxygen adsorbed on the surface of the crystallites. The spatial distribution of the potential in a crystallite is calculated, demonstrating a substantial change in the height and profile of the intercrystallite barriers as a result of the drift of defects.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, 18–22, July, 1982. 相似文献
8.
《Journal of luminescence》1987,39(2):111-116
We present time-resolved luminescence results on CdS0.36Se0.64 which give a new insight on the kinetics of excitons localized by alloy potential fluctuations. By exciting in the localized exciton band with detection close to the exciting wavelength we obtain the lifetime across the band. Below the exciting laser energy two processes contribute to luminescence: transfer of localized excitons by tunnel effect assisted by acoustical phonons, and luminescence (assisted by acoustical phonons) of all the states excited at time t = 0 either directly or through their acoustical absorption wing. The time behavior of luminescence with respect to the detuning from the exciting energy helps to discriminate between those two contributions. Furthermore it shows that intermediate long-living states are involved in the exciton relaxation process. 相似文献
9.
N.V. Bondar 《Journal of luminescence》2010,130(1):1-7
The optical spectra of quantum dots (QDs) of CdS and ZnSe grown in borosilicate glass by the sol-gel method are obtained and analyzed. It is found that at concentrations of the two semiconductors x<0.06% the emission spectra are due to annihilation of free (internal) excitons in quantum states. The mean size of the quantum dots for a given concentration of ZnSe and CdS is calculated and found to be in good agreement with the X-ray data, and the exciton binding energy is calculated with allowance for the dielectric mismatch between the semiconductor and matrix. It is proposed that this mismatch may be the cause giving rise to the exciton percolation level that is observed in QD arrays for both systems at x>0.06%. The emission from the surface level of CdS QDs in the region ~2.7 eV, formed by the outer atoms with dangling bonds, is observed for the first time, as is the emission band from surface localized states. The relation between the position of the maximum of this band and the energy of the 1S state of the free exciton is established. It is shown that the properties of surface localized states are largely similar to the analogous properties of localized states of 3D (amorphous semiconductors, substitutional solid solutions of substitution) and 2D (quantum wells and superlattices) structures. 相似文献
10.
Majumder F. A. Shevel S. Lyssenko V. G. Swoboda H. E. Klingshirn C. 《Zeitschrift für Physik B Condensed Matter》1987,66(4):409-418
The absorption-, reflection-, and luminescence spectra of CdS1–x
Se
x
are measured under low excitation. The luminescence under high excitation is also observed. For the first time, the gain spectra of disordered crystals are investigated with the excite- and probebeam technique to get a better understanding of the high density electron-hole pair system in this type of materials. We compare the results with those obtained in pure CdS and CdSe. 相似文献
11.
We report experimental results on the creation of 2P excitons in CdS by the two-photon magneto-absorption process involving a simultaneous absorption of visible and infrared photons. For a magnetic field parallel to the c axis and particularly for a visible beam propagating along the c axis, spin-oriented 2P (A) excitons are created from the A (Γ9) valence band. We explain these results on the basis of the main contribution of the 1SΓ5 (A) exciton intermediate state. 相似文献
12.
S. Vielhauer V. Babin M. De Grazia E. Feldbach M. Kirm V. Nagirnyi A. Vasil’ev 《Physics of the Solid State》2008,50(9):1789-1794
Using free electron laser excitation in the XUV range, CaWO4 samples were exposed to ultrashort intense photon pulses (photon energy, 89.84 eV; average pulse energy, 10 μJ; pulse length,
25 fs), and their luminescence was studied with time-resolved spectroscopy. In the decay curves measured in the temperature
range 8–300 K, a nonexponential emission decay with shortening of the lifetimes over the first few microseconds was observed,
depending on the excitation density. Using a model for dipole-dipole interaction of excitons under nonuniform excitation densities,
the structure of the decay curves can be reproduced in good agreement with the experimental data, and parameters for the initial
exciton interaction can be calculated.
The text was submitted by the authors in English. 相似文献
13.
14.
Poulter AJ Zeman J Maude DK Potemski M Martinez G Riedel A Hey R Friedland KJ 《Physical review letters》2001,86(2):336-339
Magneto infrared absorption measurements have been performed in a highly doped GaAs quantum well which has been lifted off and bonded to a silicon substrate, in order to study the resonant polaron interaction. It is found that the pinning of the cyclotron energy occurs at an energy close to that of the transverse optical phonon of GaAs. This unexpected result is explained by a model taking into account the full dielectric constant of the quantum well. 相似文献
15.
16.
Sharp absorption lines near the fundamental edge caused by planar stacking faults in BiI3 crystals have been investigated on absorption and luminescence spectra. Under high excitation-photon densities these lines show peak-shift and line broadening. The high density effects on the exciton bound at the defects shows a two-dimensional feature of the exciton motion. 相似文献
17.
18.
Time-resolved luminescence spectra are measured at 4.2 K most in detail for CdSe under 531 nm pico-second pulse excitation. The M, P, and A-LO lines from high density excitons rise in intensity after pulse excitation, reach maxima, and then fall, the rise time being in a range of 100–600 psec and becoming faster with increasing excitation density. This time dependence is due to the light amplification effect by stimulated emission. 相似文献
19.
A new luminescence line characterized by a broad spectral width appears under intense pico-second pulse excitation at 4.2 K in both CdSe and CdS. With increasing excitation density the peak of the line shifts to lower energies and the spectral width becomes broader. Just opposite changes are observed with the lapse of time after excitation. It is concluded that the line is due to high density electron-hole plasma. 相似文献
20.
The optical absorption spectra of alkali cyanides in the UV region present a set of weak absorption bands which are identified as triplet a'3Σ+ molecular excitons. The nature of the molecular exciton transitions in the ionic-molecular crystals is discussed and the existence of an admixture between molecular exciton and charge transfer exciton states is suggested. 相似文献