Showing papers on "Exciton published in 2000"
TL;DR: In this article, the splitting of the valence band by crystal field and spin-orbit interaction has been calculated and measured, and the measured values agree with the calculated values and the effects of strain on the splitting and optical properties have been studied in detail.
Abstract: During the last few years the developments in the field of III–nitrides have been spectacular. High quality epitaxial layers can now be grown by MOVPE. Recently good quality epilayers have also been grown by MBE. Considerable work has been done on dislocations, strain, and critical thickness of GaN grown on different substrates. Splitting of valence band by crystal field and by spin-orbit interaction has been calculated and measured. The measured values agree with the calculated values. Effects of strain on the splitting of the valence band and on the optical properties have been studied in detail. Values of band offsets at the heterointerface between several pairs of different nitrides have been determined. Extensive work has been done on the optical and electrical properties. Near band-edge spectra have been measured over a wide range of temperatures. Free and bound exciton peaks have been resolved. Valence band structure has been determined using the PL spectra and compared with the theoretically calcu...
1,202 citations
TL;DR: In this paper, the effect of the electron-hole Coulomb interaction on the optical spectra of nanocrystals was analyzed and a theory of the quantum size levels in wide gap (CdSe) and narrow gap semiconductors (InAs) was presented.
Abstract: ▪ Abstract We review the rapid progress made in our understanding of the crystal properties of semiconductors and nanocrystals focussing on theoretical results obtained within the multiband effective mass approximation. A comparison with experiment shows these results are valid for nanocrystals down 22–26 A in diameter. The effect of the electron-hole Coulomb interaction on the optical spectra is analyzed. A theory of the quantum–size levels in wide gap (CdSe) and narrow gap semiconductors (InAs) is presented that describes the absorption spectra of these semiconductors well. A great enhancement of the electron-hole exchange interaction leads to the formation of the optically forbidden Dark Exciton in nanocrystals, which strongly affects their photoluminescence. A theory of the band-edge exciton fine structure is presented and applied to the study of the PL in CdSe nanocrystals. The effect of doping on nanocrystal spectra is considered. The enhancement of the short–range spin-spin interaction in Mn-doped ...
836 citations
TL;DR: In this article, the results of steady-state and time-resolved luminescence measurements performed on suspensions of nanocrystalline ZnO particles of different sizes and at different temperatures are presented.
Abstract: This report presents the results of steady-state and time-resolved luminescence measurements performed on suspensions of nanocrystalline ZnO particles of different sizes and at different temperatures. In all cases two emission bands are observed. One is an exciton emission band and the second an intense and broad visible emission band, shifted by approximately 1.5 eV with respect to the absorption onset. As the size of the particles increases, the intensity of the visible emission decreases while that of the exciton emission increases. As the temperature decreases, the relative intensity of the exciton emission increases. In accordance with the results presented in a previous paper, we assume that the visible emission is due to a transition of an electron from a level close to the conduction band edge to a deeply trapped hole in the bulk ( ) of the ZnO particle. The temperature dependence and size dependence of the ratio of the visible to exciton luminescence and the kinetics are explained by a model in w...
827 citations
TL;DR: The presence of interchain species in the photophysics of conjugated polymer films has been the subject of a great deal of controversy as discussed by the authors, and much of the controversy can be resolved by noting that the polymer samples in different studies had different side groups or were prepared in different ways and thus have different degrees of inter-chain interaction.
Abstract: The presence of interchain species in the photophysics of conjugated polymer films has been the subject of a great deal of controversy. In this paper, we present strong evidence that interchain species do form in conjugated polymer films, and that the degree of interchain interactions can be controlled by varying the solvent and polymer concentration of the solution from which the films are cast. Thus, much of the controversy in the literature can be resolved by noting that the polymer samples in different studies had different side groups or were prepared in different ways and thus have different degrees of interchain interaction. The photoluminescence (PL) of poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene), MEH-PPV, changes both its spectral shape and quantum yield when the films are prepared from different solutions or when the morphology is varied by annealing. Increasing the amount of interchain interactions enhances the red portion of the film’s PL, a result assigned to a combination of changes in the vibronic structure of the PL of the exciton and increased numbers of weakly emissive interchain species. Photoluminescence excitation spectroscopy shows that excitation to the red edge of the absorption band preferentially enhances the red emission, suggesting that the interchain species are aggregates with a distinct ground state absorption. Scanning force microscopy shows topographic features that correlate with the degree of interchain interactions, verifying that the morphology of conjugated polymer films changes with polymer concentration, choice of solvent, and spin-casting speed. Even at low excitation intensities, photooxidative damage occurs quickly in MEH-PPV films excited in air, and the rate at which damage occurs is sensitive to the packing of the polymer chains. For samples under vacuum at low excitation intensity, a long-lived emissive tail, in combination with excitedstate absorption dynamics that do not match those of the emissive species, provide direct evidence for the production of interchain aggregates. Annealing an MEH-PPV film produces a photophysical signature similar to photooxidation, implying that defects in conjugated polymer films are intrinsic and depend on the details of how the chains are packed. At higher excitation intensities, we find that exciton -exciton annihilation occurs, and that the probability for annihilation can vary by an order of magnitude depending on the degree of interchain contact in the film. Finally, we show that changing the film morphology has a direct effect on the performance of MEH-PPV-based light-emitting diodes. Higher degrees of interchain interaction enhance the mobility of carriers at the expense of lower quantum efficiencies for electroluminescence. Taken together, the results reconcile much of the contradictory literature and provide a prescription for the optimization of conjugated polymer films for particular device applications.
784 citations
TL;DR: It is found that the emission energy changes abruptly whenever an electron is added to the artificial atom, and that the sizes of the jumps reveal a shell structure.
Abstract: Quantum dots or rings are artificial nanometre-sized clusters that confine electrons in all three directions. They can be fabricated in a semiconductor system by embedding an island of low-bandgap material in a sea of material with a higher bandgap. Quantum dots are often referred to as artificial atoms because, when filled sequentially with electrons, the charging energies are pronounced for particular electron numbers; this is analogous to Hund's rules in atomic physics. But semiconductors also have a valence band with strong optical transitions to the conduction band. These transitions are the basis for the application of quantum dots as laser emitters, storage devices and fluorescence markers. Here we report how the optical emission (photoluminescence) of a single quantum ring changes as electrons are added one-by-one. We find that the emission energy changes abruptly whenever an electron is added to the artificial atom, and that the sizes of the jumps reveal a shell structure.
782 citations
Book•
11 Feb 2000
TL;DR: In this article, the electronic and Vibrational Molecular States Dynamics of Isolated and Open Quantum Systems (ISMs) were discussed, including VNE, energy relaxation, and redistribution.
Abstract: Electronic and Vibrational Molecular States Dynamics of Isolated and Open Quantum Systems Vibrational Energy Relaxation and Redistribution Intramolecular Electronic Transitions Electron Transfer Proton Transfer Exciton Transfer Concluding Remarks
628 citations
TL;DR: This work demonstrates that by increasing the doping level of Doped π-conjugated polymer layers, the barrier to hole injection can be continuously reduced in OLED devices with hole-limited electroluminescence, finding that it is possible to significantly reduce the operating voltage while improving the light output and efficiency.
Abstract: Organic light-emitting diodes (OLEDs) represent a promising technology for large, flexible, lightweight, flat-panel displays. Such devices consist of one or several semiconducting organic layer(s) sandwiched between two electrodes. When an electric field is applied, electrons are injected by the cathode into the lowest unoccupied molecular orbital of the adjacent molecules (simultaneously, holes are injected by the anode into the highest occupied molecular orbital). The two types of carriers migrate towards each other and a fraction of them recombine to form excitons, some of which decay radiatively to the ground state by spontaneous emission. Doped pi-conjugated polymer layers improve the injection of holes in OLED devices; this is thought to result from the more favourable work function of these injection layers compared with the more commonly used layer material (indium tin oxide). Here we demonstrate that by increasing the doping level of such polymers, the barrier to hole injection can be continuously reduced. The use of combinatorial devices allows us to quickly screen for the optimum doping level. We apply this concept in OLED devices with hole-limited electroluminescence (such as polyfluorene-based systems), finding that it is possible to significantly reduce the operating voltage while improving the light output and efficiency.
538 citations
TL;DR: In this article, the emission properties of suspensions of nanocrystalline ZnO particles with different particle sizes were studied and a linear relationship between the energetic maxima of the two emission bands was found.
509 citations
TL;DR: In this article, the steady-state luminescence measurements performed on suspensions of nanocrystalline ZnO particles of different sizes are presented, and a model is presented in which the visible emission is assigned to the radiative recombination of an electron from a level close to the conduction band edge and a deeply trapped hole in the bulk (V.. o ) of the particle.
428 citations
TL;DR: In this article, the feasibility of ZnO as photonic material for the UV region was addressed and it was concluded that ZnOs can be used for exciton-based photonic device applications owing to the high exciton binding energy.
Abstract: This paper will address the feasibility of ZnO as photonic material for the UV region. ZnO films are grown by plasma-assisted MBE. Detailed XRD studies suggest the growth of structurally different epilayers on Al2O3 (0001) and MgAl2O4 (111) substrates. PL shows dominant excitonic emission and very low deep level emission which is indicative of low density of defects or impurities. Stimulated emission based on the excitonic mechanism has been achieved up to 550 K. It is concluded that ZnO can be used for exciton-based photonic device applications owing to the high exciton binding energy. Optically pumped lasing has been demonstrated at room temperature.
410 citations
TL;DR: Time-resolved single-molecule data demonstrate that the 580-nanometer conformation exhibits a "landscape" for intramolecular electronic energy relaxation with a "funnel" that contains a 580- nanometer singlet exciton trap at the bottom.
Abstract: The photochemistry of poly[2-methoxy, 5-(2′-ethyl-hexyloxy)-p-phenylene-vinylene] (MEH-PPV) has been found to be highly dependent on the presence of O2, which increases singlet exciton quenching dramatically. Spectroscopy on isolated single molecules of MEH-PPV in polycarbonate films that exclude O2 reveals two distinct polymer conformations with fluorescence maxima near 555 and 580 nanometers wavelength, respectively. Time-resolved single-molecule data demonstrate that the 580-nanometer conformation exhibits a “landscape” for intramolecular electronic energy relaxation with a “funnel” that contains a 580-nanometer singlet exciton trap at the bottom. The exciton traps can be converted to exciton quenchers by reaction with O2. Conformationally induced, directed-energy transfer is arguably a critical dynamical process that is responsible for many of the distinctive photophysical properties of conjugated polymers.
TL;DR: In this article, the excitons recombined within Si nanocrystals through a strong coupling mechanism, and the Er excitation process at room temperature occurs at a submicrosecond time scale.
Abstract: Silicon nanocrystals were formed in SiO2 using Si ion implantation followed by thermal annealing. The nanocrystal-doped SiO2 layer was implanted with Er to a peak concentration of 1.8 at. %. Upon 458 nm excitation the sample shows a broad nanocrystal-related luminescence spectrum centered around 750 nm and two sharp Er luminescence lines at 982 and 1536 nm. By measuring the excitation spectra of these features as well as the temperature-dependent intensities and luminescence dynamics we conclude that (a) the Er is excited by excitons recombining within Si nanocrystals through a strong coupling mechanism, (b) the Er excitation process at room temperature occurs at a submicrosecond time scale, (c) excitons excite Er with an efficiency >55%, and (d) each nanocrystal can have at most ~1 excited Er ion in its vicinity.
TL;DR: In this article, the exciton states in quasi-one-dimensional organic crystals with strong orbital overlap between neighboring molecules were considered and a Hamiltonian model was proposed to explain the main features of the low temperature absorption spectra.
TL;DR: In this paper, the authors applied quantum-chemical techniques to describe the description of electronic excitations in interacting conjugated chains and examined cofacial dimers formed by linear polyene chains of various lengths and used two strategies to compute the exciton coupling energy.
Abstract: Correlated quantum-chemical techniques are applied to the description of electronic excitations in interacting conjugated chains. The focus is on the magnitude and conjugation-length dependence of the splitting of the lowest optically allowed excitonic state, which is induced by interchain interactions. We first examine cofacial dimers formed by linear polyene chains of various lengths and use two strategies to compute the exciton coupling energy. One is based on molecular exciton theory, which assumes that the excited-state wave functions of the isolated chains remain unperturbed by the intermolecular forces; in the other, the supermolecular approach, the wave functions are obtained from molecular orbital calculations performed for the whole system and are therefore not constrained to a single chain. We find that the two techniques lead to consistent results, provided an appropriate form for the interchain Coulomb interactions is adopted in the excitonic model. In particular, both formalisms indicate a p...
TL;DR: Application of the molecular orbital perturbation approach to a model system for poly-(paraphenylenevinylene) shows that the ratio between the electroluminescence and photoluminescent quantum yields generally exceeds the 25% spin-degeneracy statistical limit.
Abstract: By applying a molecular orbital perturbation approach, we calculate the formation rates for singlet and triplet molecular excitons associated with intermolecular charge-transfer processes. It is found that the interchain bond-charge correlation has a strong influence on the relative probabilities for generating singlet and triplet excitons. Most importantly, application of our approach to a model system for poly-(paraphenylenevinylene) shows that the ratio between the electroluminescence and photoluminescence quantum yields generally exceeds the 25% spin-degeneracy statistical limit.
TL;DR: High electron and hole mobilities as well as balanced charge carrier injection lead to improved exciton generation in these gate-controlled devices and the effect of charge-induced absorption is substantially reduced in high-quality single crystals compared with amorphous organic materials.
Abstract: We report on electrically driven amplified spontaneous emission and lasing in tetracene single crystals using field-effect electrodes for efficient electron and hole injection. For laser action, feedback is provided by reflections at the cleaved edges of the crystal resulting in a Fabry-Perot resonator. Increasing the injected current density above a certain threshold value results in the decreasing of the spectral width of the emission from 120 millielectron volts to less than 1 millielectron volt because of gain narrowing and eventually laser action. High electron and hole mobilities as well as balanced charge carrier injection lead to improved exciton generation in these gate-controlled devices. Moreover, the effect of charge-induced absorption is substantially reduced in high-quality single crystals compared with amorphous organic materials.
TL;DR: In this article, the photoluminescence properties of ZnO films grown on CaF2(111) with a low-temperature buffer layer by plasma assisted molecular beam epitaxy are investigated, in which lattice misfit tensile strain is expected to be compensated by the thermal compressive strain.
Abstract: Photoluminescence (PL) properties of ZnO films grown on CaF2(111) with a low-temperature buffer layer by plasma assisted molecular beam epitaxy are investigated, in which lattice misfit tensile strain is expected to be compensated by the thermal compressive strain. The low-temperature buffer layer is further introduced to accommodate lattice strain leading to the growth of almost strain-free and high quality ZnO films. PL spectra of ZnO layers measured at 10 K are dominated by neutral-donor bound exciton emission at 3.366 eV (I4) with a linewidth of 12 meV. Commonly observed deep level emission at around 2.3 eV is negligibly small in intensity. Free exciton emission develops as temperature is raised and eventually dominates at temperatures higher than 70 K. Detailed study on temperature-dependent PL spectra indicates that the energy position of the free exciton emission is located at the same energy as bulk materials suggesting the growth of strain-free ZnO layers. Consequently, stimulated emission due to exciton–exciton scattering is observed at 77 K.
TL;DR: Results for microcavities containing two spatially separated cyanine dyes are presented, where simultaneous strong coupling of the excitations of the individual dyes to a single cavity mode leads to new eigenmodes, described as admixtures of all three states.
Abstract: Coherent excitations of intricate assemblies of molecules play an important role in natural photosynthesis. Microcavities are wavelength-dimension artificial structures in which excitations can be made to couple through their mutual interactions with confined photon modes. Results for microcavities containing two spatially separated cyanine dyes are presented here, where simultaneous strong coupling of the excitations of the individual dyes to a single cavity mode leads to new eigenmodes, described as admixtures of all three states. These “hybrid” exciton-photon structures are of potential interest as model systems in which to study energy capture, storage, and transfer among coherently coupled molecular excitations.
TL;DR: In this article, the coupling strengths of exciton-acoustic phonon and excitonlongitudinal-optical phonon were directly determined from the temperature dependence of the exciton absorption spectra independently for A and B excitons, which are close in energy and obey the same selection rule for each other.
Abstract: Optical properties in undoped-ZnO epilayers grown by the laser-molecular-beam epitaxy method on lattice-matched ScAlMgO4 substrates were investigated. The absorption spectrum at 5 K has two sharp peaks, both of which are attributed to resonances of A and B excitons, which reflect a small nonradiative damping constant of excitons as well as high film crystallinity accomplished by the virtue of lattice matching. The coupling strengths of exciton-acoustic phonon and of exciton–longitudinal-optical phonon were directly determined from the temperature dependence of exciton absorption spectra independently for A and B excitons, which are close in energy and obey the same selection rule for each other.
TL;DR: In this article, the photoluminescence (PL) spectrum at 12 K peaks at 1.60 eV and has a full width at half maximum of 0.28 eV.
Abstract: Silicon nanocrystals with diameters ranging from [approximate]2 to 5.5 nm were formed by Si ion implantation into SiO2 followed by annealing. After passivation with deuterium, the photoluminescence (PL) spectrum at 12 K peaks at 1.60 eV and has a full width at half maximum of 0.28 eV. The emission is attributed to the recombination of quantum-confined excitons in the nanocrystals. The temperature dependence of the PL intensity and decay rate at several energies between 1.4 and 1.9 eV was determined between 12 and 300 K. The temperature dependence of the radiative decay rate was determined, and is in good agreement with a model that takes into account the energy splitting between the excitonic singlet and triplet levels due to the electron-hole exchange interaction. The exchange energy splitting increases from 8.4 meV for large nanocrystals ([approximate]5.5 nm) to 16.5 meV for small nanocrystals ([approximate]2 nm). For all nanocrystal sizes, the radiative rate from the singlet state is 300–800 times larger than the radiative rate from the triplet state.
TL;DR: In this paper, a significantly narrower size distribution of ZnS nanocrystals than reported in earlier published results was obtained, and band gap luminescence was observed in mercaptoethanol capped ZnSRs.
Abstract: Optical measurements on ZnS nanoclusters have been carried out to investigate surface effects along with quantum size effects. ZnS nanocrystals have been synthesized in the range of 1.5–2.5 nm, using different chemical methods as well as electronic passivating procedures. The size of nanoparticles has been estimated from empirical pseudopotential calculations. We have obtained a significantly narrower size distribution of ZnS nanocrystals than reported in earlier published results. We observed band gap luminescence in mercaptoethanol capped ZnS nanocrystals. Effects of various defect levels on the luminescent behavior of ZnS nanoparticles have been examined
Patent•
15 Nov 2000TL;DR: In this paper, an organic photosensitive optoelectronic device having a plurality of cells disposed between a first electrode and a second electrode is defined, where each cell includes a photoconductive organic hole transport layer adjacent to a photoconductorive organic electron transport layer.
Abstract: An organic photosensitive optoelectronic device having a plurality of cells disposed between a first electrode and a second electrode. Each cell includes a photoconductive organic hole transport layer adjacent to a photoconductive organic electron transport layer. A metal or metal substitute is disposed between each of the cells. At least one exciton blocking layer is disposed between the first electrode and the second electrode.
TL;DR: In this article, the effects of the built-in electric field in photoluminescence spectroscopy quantum wells were investigated and quantitatively explained by means of a self-consistent tight-binding model that includes screening (either dielectric or by free-carriers), piezoelectric field and spontaneous polarization field.
Abstract: We have investigated the effects of the built-in electric field in ${\mathrm{G}\mathrm{a}\mathrm{N}/\mathrm{A}\mathrm{l}}_{0.15}{\mathrm{Ga}}_{0.85}\mathrm{N}$ quantum wells by photoluminescence spectroscopy. The fundamental electron heavy-hole transition redshifts well below the GaN bulk gap for well widths larger than 3 nm for the specific quantum wells investigated and exhibits a concomitant reduction of the intensity with increasing well thickness. The experimental data are quantitatively explained by means of a self-consistent tight-binding model that includes screening (either dielectric or by free-carriers), piezoelectric field and spontaneous polarization field. The impact of the built-in field on the exciton stability is discussed in detail. We demonstrate that the exciton binding energy is substantially reduced by the built-in field, well below the values expected from the quantum size effect in the flat band condition.
TL;DR: In this paper, a novel detonation initiation mechanism for solid explosives is proposed based on electronic excitations induced by an impact wave propagating through the crystal, where a key role belongs to lattice defects, in particular edge dislocations, which promote dramatic changes in the electronic structure, primarily a reduction of the optical gap due to splitting off of local electronic states from both valence and conduction bands.
Abstract: A novel mechanism for detonation initiation in solid explosives is proposed. This is based on electronic excitations induced by an impact wave propagating through the crystal. We illustrate the model by using the RDX (C3H6N6O6) crystal as an example. In our model, a key role belongs to lattice defects, in particular edge dislocations, which promote dramatic changes in the electronic structure, primarily a reduction of the optical gap due to the splitting off of local electronic states from both valence and conduction bands. The pressure inside the impact wavefront further reduces the band gap, making it close to zero. This promotes highest occupied molecular orbital–lowest unoccupied molecular orbital HOMO–LUMO transitions resulting in N–NO2 bond breaking and the creation of favorable conditions for the initiation of a chain reaction. Experimental facts supporting the suggested mechanism are discussed.
TL;DR: In this article, the authors used time-resolved photoluminescence spectroscopy at 2 K to measure the radiative recombination lifetime of the allowed and forbidden free excitons in ZnO.
Abstract: Time-resolved photoluminescence spectroscopy at 2 K was used to measure the radiative recombination lifetime of the allowed (Γ5) and forbidden (Γ6) free excitons in ZnO. The measurements were made on a sample containing internal strain, which altered the sample symmetry, and resulted in relaxed selection rules, allowing the Γ6 exciton to be observed. A radiative recombination lifetime of 259 ps was measured for the Γ5 exciton and 245 ps for the Γ6 exciton. The decay of the free excitons was of single-exponential form, and the decay times were obtained using a least-squares fit of the data.
TL;DR: In this article, the authors used time-resolved photoluminescence spectroscopy to investigate carrier decay dynamics in a InxGa1−xAs1−yNy (x∼0.03, y∼ 0.01) epilayer grown on GaAs by metal organic chemical vapor deposition.
Abstract: Time-resolved photoluminescence spectroscopy has been used to investigate carrier decay dynamics in a InxGa1−xAs1−yNy (x∼0.03, y∼0.01) epilayer grown on GaAs by metal organic chemical vapor deposition. Time-resolved photoluminescence (PL) measurements, performed for various excitation intensities and sample temperatures, indicate that the broad PL emission at low temperature is dominated by localized exciton recombination. Lifetimes in the range of 0.07–0.34 ns are measured; these photoluminescence lifetimes are significantly shorter than corresponding values obtained for GaAs. In particular, we observe an emission energy dependence of the decay lifetime at 10 K, whereby the lifetime decreases with increasing emission energy across the PL spectrum. This behavior is characteristic of a distribution of localized states, which arises from alloy fluctuations.
TL;DR: In this article, the authors investigated the low-temperature band-edge photoluminescence (PL) of ZnO films prepared by spray pyrolysis and revealed a complicated multi-line structure.
TL;DR: In this article, the absorption and photoluminescence spectra of the MEH-PPV polymer in a chloroform solvent were analyzed and the energy level of the emissive S1 state of the oligomer and the corresponding oscillator strength were calculated from exciton theory.
Book•
27 Sep 2000
TL;DR: In this paper, the authors studied the effect of vibrant tunneling into Exciton and Polariton States on photoluminescence and Stimulated Emission of Exciton Polaritons.
Abstract: Microcavity Exciton Polaritons.- Biexcitonic Effects in Microcavities.- Resonant Tunneling into Exciton and Polariton States.- Competition Between Photon Lasing and Exciton Lasing.- Polariton Dynamics in Photoluminescence.- Stimulated Emission of Exciton Polaritons.
TL;DR: In this paper, a band-tail model was used to study the exciton localization effect of increasing the thickness of a single-quantum-well structure up to 2.5 nm.
Abstract: Temperature-dependent photoluminescence (PL) measurements are performed on In0.23Ga0.77N/GaN single-quantum-well structures with different well thickness. Based on a band-tail model, the exciton localization effect is studied. The exciton localization effect is enhanced by increasing quantum-well thickness up to 2.5 nm. If the quantum-well thickness is further increased to above 2.5 nm, the exciton localization effect becomes weak. Finally, when the quantum-well thickness is increased to 5 nm, the exciton localization effect cannot be observed. In addition, the PL intensity decreases monotonically with increasing the quantum-well thickness. In connection with an excitation-power dependent PL measurement, the result of the quantum-well thickness dependent PL intensity can be attributed to quantum confined Stark effect, which becomes particularly strong in the wide quantum-well structure. Based on our optical investigation, the presented article indicates that the emission mechanism is dominated by the exci...