共查询到20条相似文献,搜索用时 31 毫秒
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U. Woggon O. Wind F. Gindele E. Tsitsishvili M. Mü ller 《Journal of luminescence》1996,70(1-6):269-280
The optical transition energies have been determined for the lowest electron-hole pair states of CdSe quantum dots embedded in glass. The data obtained by photoluminescence, differential absorption and photoluminescence excitation spectroscopy have been compared and a general size dependence could be established. Based on theoretical calculations, the dominant features in the spectra have been assigned to the different transitions from the ground state to the one-pair states. Within the lowest one pair transition, a fine structure due to exchange interaction has been observed. The change in the optical properties with increasing intensity has been studied and the two-pair states identified in luminescence. Spectrally broad optical gain has been found due to stimulated transitions involving both one- and two-pair states. 相似文献
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A. F. Zatsepin 《Physics of the Solid State》2010,52(6):1176-1187
The parameters of excited states of oxygen-deficient centers (ODCs) in high-energy-electron irradiated crystalline and glassy
SiO2 have been studied using optical absorption, luminescence, and photoelectron emission spectroscopy. Additional evidence has
been gained in support of the model of a neutral oxygen vacancy in ODCs, the diagram of electronic transitions has been refined,
and their characteristics have been quantified. The possibility of ionization of the singlet and triplet defect states at
a transition to the anomalously relaxed configuration has been demonstrated using the particular example of α-ODCs. Nonradiative
excitation transfer from nonbridging oxygen centers to the triplet ODC state has been observed. 相似文献
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N. N. Zinov’ev A. V. Andrianov V. Yu. Nekrasov V. A. Petrovskii L. V. Belyakov O. M. Sreseli G. Hill J. M. Chamberlain 《JETP Letters》2001,74(2):100-102
Terahertz electroluminescence in the range ≈1.5 THz was observed in a quantum-cascade GaAs/AlGaAs structure containing 40 periods of tunnel-coupled wells. The luminescence is caused by the spatially indirect optical electron transitions between the ground states of neighboring quantum wells. 相似文献
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Three sharp absorption features in the energy range 2.36–2.55 eV have been detected in the transmission spectrum of Co-diffused ZnSe, and a number of luminescence transitions originating from the lowest of these states at 2.361 eV have been observed. Photoluminescence excitation spectra prove that these are high energy excited states of the Co2+Zn impurity, a conclusion confirmed by comparison of measured and predicted luminescence energies. This represents the first identification of luminescence branching from a higher excited state of a transition metal ion in any semiconductor. The sharp, weakly phonon-coupled transitions involve either intra-impurity excitation or transitions from the impurity to localised states split off from a minimum in the conduction band. The implications of these observations for the mechanism of host-impurity energy transfer and for the nature of the excited state wavefunctions are discussed. 相似文献
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A wide class of experimental data on luminescence in doped two-dimensional systems is explained in terms of multiphonon optical transitions. A zero-radius-potential model is employed to describe localized states in square quantum wells. Specifically, it is shown that the luminescence intensity varies nonmonotonically with the acceptor-impurity position, whereas the half-width of the luminescence peak decreases with the impurity distance from the center of the size-confined system. The features of luminescence in a longitudinal magnetic field are investigated. 相似文献
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B. A. Zadorozhnyi 《Journal of Applied Spectroscopy》1966,5(3):260-263
The reasons for the simultaneous presence of two emission bands, blue and red, in the fluorescence spectra of certain aromatic o-hydroxycarboxylic acids and their derivatives have been examined. It was shown that the unusual luminescence properties of these compounds were determined by the large differences in energy of the intramolecular hydrogen bonds in the normal and excited electronic states. The long-wave luminescence bands in similar cases are the result of optical transitions in the high frequency sublevels of the ground electronic state (sometimes in the dissociaton region of the hydrogen bond). 相似文献
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The authors present the application of contactless electroreflectance (CER) spectroscopy to study optical transitions in low
dimensional semiconductor structures including quantum wells (QWs), step-like QWs, quantum dots (QDs), quantum dashes (QDashes),
QDs and QDashes embedded in a QW, and QDashes coupled with a QW. For QWs optical transitions between the ground and excited
states as well as optical transitions in QW barriers and step-like barriers have been clearly observed in CER spectra. Energies
of these transitions have been compared with theoretical calculations and in this way the band structure has been determined
for the investigated QWs. For QD and QDash structures optical transitions in QDs and QDashes as well as optical transitions
in the wetting layer have been identified. For QDs and QDashes surrounded by a QW, in addition to energies of QD and QDash
transitions, energies of optical transitions in the surrounded QW have been measured and the band structure has been determined
for the surrounded QW. Finally some differences, which can be observed in CER and photo-reflectance spectra, have been presented
and discussed for selected QW and QD structures. 相似文献
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利用等离子体化学气相沉积技术在100℃的衬底温度下,制备了具有不同组分比的系列非晶碳化硅薄膜。结合傅里叶变换红外光谱与喇曼光谱对所制备的薄膜微结构进行了表征与分析,同时,对具有不同组分比的非晶碳化硅薄膜室温光致发光性质进行了系统的研究。结果表明在Ar+离子激光和Xe灯紫外光的激发下,不同组分的样品显示出不同的光致发光特性,并对样品的发光特性与其微结构的联系进行了讨论。在此基础上,用碳化硅薄膜设计和制备了全固体光学微腔,研究了微腔对碳化硅发光行为的调制作用。 相似文献
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A broad visible luminescence band and characteristic IR luminescence of Yb(3+) ions are observed under UV excitation in ytterbium-doped aluminosilicate glass. Samples made under both oxidizing and reducing conditions are analyzed. A strong charge-transfer absorption band in the UV range is observed for glass samples containing ytterbium. Additional absorption bands are observed for the sample made under reducing conditions, which are associated with f-d transitions of divalent ytterbium. The visible luminescence band is attributed to 5d-4f emission from Yb(2+) ions, and the IR luminescence is concluded to originate from a relaxed charge-transfer transition. The findings are important to explain induced optical losses (photodarkening) in high-power fiber lasers. 相似文献
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A review of the electronic dipole transitions in graphite and single-wall carbon nanotubes is presented. Because of its singular electronic structure, the optical absorption matrix element as a function of wave vector has a node in the two-dimensional Brillouin zone of graphite, which depends linearly on the optical polarization direction. In the case of the single-wall carbon nanotubes, the dipole selection rule and the van Hove singularity in the joint density of states will give a characteristic behavior, which is observed by luminescence and resonance Raman spectroscopy. PACS 78.30.Na; 78.20.Bh; 78.66.Tr; 63.22.+m; 36.20.Kd; 36.20.Ng 相似文献
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Y. Toda O. Moriwaki M. Nishioka Y. Arakawa 《Physica E: Low-dimensional Systems and Nanostructures》2000,8(4)
We have investigated the carrier relaxation mechanism in InGaAs/GaAs quantum dots by photoluminescence excitation (PLE) spectroscopy. Near-field scanning optical microscope successfully shows that a PLE resonance at a relaxation energy of 36 meV can be seen in all single-dot luminescence spectra, and thus can be attributed to resonant Raman scattering by a GaAs LO phonon to the excitonic ground state. In addition, a number of sharp resonances observed in single-dot PLE spectra can be identified as resonant Raman features due to localized phonons, which are observed in the conventional Raman spectrum. The results reveal the mechanism for the efficient relaxation of carriers observed in self-assembled quantum dots: the carriers can relax within the continuum states, and make transitions to the excitonic ground state by phonon emission. 相似文献
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We have studied the photoluminescence of Ge samples cleaved in ultra-high vacuum to better understand the role of intrinsic surface states in radiative and non-radiative recombination. We find that the surface states associated with the as-cleaved surface (2 × 1 reconstructed 〈111〉) are very efficient in quenching the band-to-band recombination at T ~ 90 K. The transitions through surface states are predominantly non-radiative. The adsorption of oxygen, up to a half monolayer, markedly reduces this quenching effect by removing the surface state bands. Some preliminary experimental results on the question of radiative transitions involving the surface states is presented. No luminescence unambiguously attributable to surface state transitions is observed for wavelengths shorter than 5 μm. 相似文献
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Specific features of optical and nonradiative transitions in molecular systems in the field of an intense electromagnetic wave are studied with account of squeezed vibrational states. It is shown that a field of laser radiation considerably enhances the tunneling processes in electronic vibrational systems and makes it possible to obtain the generation of higher harmonics. Conditions are found under which squeezed vibrational states can lead to some stabilization of excited electronic states with respect to the processes of luminescence. 相似文献
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Emission and excitation spectra, luminescence polarization and decay kinetics have been studied for CsI:Pb crystals in the 0.36-300 K temperature range. The origin of the excited states responsible for the optical characteristics has been discussed. It has been concluded that the doublet ≈3.70 eV absorption (excitation) band is caused by the electronic transitions into the Pb2+ triplet state split due to the presence of a cation vacancy near a Pb2+ ion, while the higher-energy bands are of the charge-transfer origin. Like in CsI:Tl, four emission bands of CsI:Pb have been found to belong to the main luminescence centres. Two emission bands, peaking at 3.1 and 2.6 eV, are suggested to arise from the triplet relaxed excited state of a Pb2+ ion. Two visible emission bands, peaking at 2.58 and 2.23 eV, are interpreted as the luminescence of an exciton localized near the Pb2+ ion. 相似文献
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Using ab initio methods and taking into account the lattice relaxation and polarization caused by the occurrence of the core hole, we have studied theoretically the cross luminescence in barium fluoride crystals in terms of the embedded-cluster approach. Two schemes of modeling of the core hole have been performed—in the form of an additional point charge and in the form of the 5p state of the barium ion. Calculations have been done both by the Hartree-Fock method and by the density functional method. We have showed that the deformation of the lattice caused by the occurrence of the core hole leads to states localized on fluorine ions of the nearest environment splitting off from the valence band of the BaF2 crystal. The cross-luminescence bands at 5.7, 6.3, and 7.1 eV are caused by transitions from these localized states. We have also showed that the low-energy edge of the cross luminescence is formed by transitions from states that are localized on ions of the second coordination sphere. 相似文献
18.
O. V. Alifanov 《Optics and Spectroscopy》2010,108(5):710-713
In terms of the adiabatic approach to determining the states of an impurity dielectric crystal, the temperature dependence
of the first moment (maximum) of the optical band that arises upon vibronic transitions in a local center is studied. It is
shown that the frequency of the band maximum and absolute temperature are linked with each other by a relation that is analogous
to the Wien’s displacement law for equilibrium radiation. This result is consistent with experimental data obtained, in particular
for F absorption and luminescence bands in alkali halide crystals. 相似文献
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V. Ballarini G. Barucca E. Bennici C. F. Pirri C. Ricciardi E. Tresso F. Giorgis 《Physica E: Low-dimensional Systems and Nanostructures》2003,16(3-4):591
All amorphous silicon-nitride planar optical microcavities operating in the visible range have been grown by plasma enhanced chemical vapor deposition. The luminescence intensity of the N-rich silicon-nitride layer from a microcavity with 6 period distributed Bragg reflectors (DBRs) is two order of magnitude higher than that of the luminescent layer without the cavity. Moreover, a strong directionality of the microcavities emission can be observed. Such results can be ascribed to the anisotropic optical density of states induced in the Fabry–Perot structure. The quality factors of the resonators are strictly correlated to the number of periods of the DBRs. 相似文献