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External electric field effect on exciton binding energy in GaAs /GaAlAs cylindrical quantum dots with asymmetric axial potential
摘要： The present study investigates theoretically the role of applied electric field on the exciton binding energy and photoluminescence energy in cylindrical quantum dot (QD) by considering an asymmetric axial potential. As a framework, we have considered the variational approach and the correlation between the electron and hole in the trial wave function within the effective-mass approximation. We have calculated the exciton binding energy of the ground state and the photoluminescence energy as the function of the geometry and the strength of the applied electric field along the growth direction of the cylinder. Our numerical findings for GaAs/Ga(1-x)Al(x)As have shown that the binding energy is decreasing function of the electric field strength. Also, we have found that the exciton binding energy is decreasing function of the QD height with and without electric field effect. Furthermore, the photoluminescence energy depends on the effects of electric field, the geometrical confinement and the aluminum concentrations in the barrier materials.
关键词： Exciton,Photoluminescence,Electric field,Asymmetric Quantum Dots
更新于2025-09-12 10:27:22
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Modulation of F?rster and Dexter Interactions in Single‐Emissive‐Layer All‐Fluorescent WOLEDs for Improved Efficiency and Extended Lifetime
摘要： White organic light-emitting diodes (WOLEDs) with thermally activated delayed fluorophor sensitized fluorescence (TSF) have aroused wide attention, considering their potential for full exciton utilization without noble-metal containing phosphors. However, performances of TSF-WOLEDs with a single-emissive-layer (SEL) still suffer from low exciton utilization and insufficient blue emission for proper white balance. Here, by modulating F?rster and Dexter interactions in SEL-TSF-WOLEDs, high efficiencies, balanced white spectra, and extended lifetimes are realized simultaneously. Given the different dependencies of F?rster and Dexter interactions on intermolecular distances, sterically shielded blue thermally activated delayed fluorescence (TADF) emitters and orange conventional fluorescent dopants (CFDs) with electronically inert peripheral units are adopted to enlarge distances of electronically active chromophores, not only blocking the Dexter interaction to prevent exciton loss but also finely suppressing the F?rster one to guarantee balanced white emission with sufficient blue components. It thus provides the possibility to maximize device performances in a large range of CFD concentrations. A record high maximum external quantum efficiency/power efficiency of 19.6%/52.2 lm W?1, Commission Internationale de L’Eclairage coordinate of (0.33, 0.45), and prolonged half-lifetime of over 2300 h at an initial luminance of 1000 cd m?2 are realized simultaneously for SEL-TSF-WOLEDs, paving the way toward practical applications.
关键词： sensitizing process,thermally activated delayed fluorescence,exciton interactions,white organic light-emitting diodes,sterically inert substituents
更新于2025-09-12 10:27:22
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Fullerene derivative layer induced phase separation and charge transport improvement for inverted polymer solar cells
摘要： The phase separation of donor and acceptor in bulk-heterojunction plays an important role on the exciton dissociation and charge carrier transport, which decides the performance of organic solar cells (OSCs). In this paper, the thin [6,6]-Phenyl-C71-butyric acid methyl ester (PC71BM) layer was incorporated as interlayer between active layer and the polyethylenemine electron transport layer of OSCs to realize high efficiency. Both a high short-circuit current density and fill factor were achieved, resulting in a power conversion efficiency up to 9.17% for the optimal device. The incorporation of PC71BM layer not only induced vertical phase separation of active layer to improve exciton dissociation and charge transfer but also modified surface morphology to increase light absorption of the active layer. This study offers a simple and lost cost strategy to improve performance of OSCs.
关键词： Light absorption,Electron transport,[6,6]-Phenyl-C71-butyric acid methyl ester,Exciton dissociation,Phase separation
更新于2025-09-12 10:27:22
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A room-temperature polariton light-emitting diode based on monolayer WS2
摘要： Exciton polaritons that arise through the strong coupling of excitons and cavity photons are used to demonstrate a wide array of fundamental phenomena and potential applications that range from Bose–Einstein-like condensation to analogue Hamiltonian simulators and chip-scale interferometers. Recently, the two-dimensional (2D) transition metal dichalcogenides (TMDs), because of their large exciton binding energies, oscillator strength and valley degree of freedom, have emerged as a very attractive platform to realize exciton polaritons at elevated temperatures. Achieving the electrical injection of polaritons is attractive both as a precursor to realizing electrically driven polariton lasers as well as for high speed light-emitting diodes (LEDs) for communication systems. Here, we demonstrate an electrically driven polariton LED that operates at room temperature using monolayer tungsten disulfide (WS2) as the emissive material. The extracted external quantum efficiency is ~0.1% and is comparable to recent demonstrations of bulk organic and carbon nanotube-based polariton electroluminescence (EL) devices. The possibility to realize electrically driven polariton LEDs in atomically thin semiconductors at room temperature presents a promising step towards achieving an inversionless electrically driven laser in these systems as well as for ultrafast microcavity LEDs using van der Waals (vdW) materials.
关键词： room temperature,transition metal dichalcogenides,exciton polaritons,van der Waals materials,electrically driven polariton LED
更新于2025-09-12 10:27:22
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The electronic and optical properties of an exciton, biexciton and charged excitons in CdSe/CdTe-based multi-shell type-II quantum dot nanocrystals
摘要： It has been recently reported that multi-shell type-II quantum dot nanocrystals (QDNCs) have higher quantum yields. Besides these higher quantum yields of multi-shell type-II QDNCs, additional second layer has been a critical influence on the formation mechanisms of the excitonic structures. Understanding of bound and unbound cases of the excitonic structures in multi-shell type-II QDNCs gives some important information for applications. In this study, we have investigated the electronic and optical properties of a single exciton (X), biexciton (XX), and positively and negatively charged excitons ( ??+ and ??? ) in CdSe/CdTe-based multi-shell type-II QDNCs. In the study, three different structure compositions, i.e., CdSe/CdTe, CdSe/CdTe/CdS, and CdSe/CdTe/ZnTe, have been considered. We have observed that CdS and ZnTe materials have drastically changed the electronic and optical properties of the bare CdSe/CdTe type-II QDNCs.
关键词： Exciton,CdS,Biexciton,CdSe/CdTe,Charged excitons,ZnTe,Quantum dot nanocrystals,Type-II
更新于2025-09-12 10:27:22
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Management of Exciton for Highly-Efficient Hybrid White Organic Light-Emitting Diodes with a Non-Doped Blue Emissive Layer
摘要： Hybrid white organic light-emitting diodes (WOLEDs) have drawn great attention both for display and solid-state lighting purposes because of the combined advantages of desirable stability of ?uorescent dyes and high e?ciency of phosphorescent materials. However, in most WOLEDs, obtaining high e?ciency often requires complex device structures. Herein, we achieved high-e?ciency hybrid WOLEDs using a simple but e?cacious structure, which included a non-doped blue emissive layer (EML) to separate the exciton recombination zone from the light emission region. After optimization of the device structure, the WOLEDs showed a maximum power e?ciency (PE), current e?ciency (CE), and external quantum e?ciency (EQE) of 82.3 lm/W, 70.0 cd/A, and 22.2%, respectively. Our results presented here provided a new option for promoting simple-structure hybrid WOLEDs with superior performance.
关键词： hybrid,exciton management,non-doped blue emissive layer,white organic light-emitting diodes
更新于2025-09-12 10:27:22
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Doubly-resonant plasmonic hot spot-exciton coupling enhances second harmonic generation from Au/ZnO hybrid porous nanosponges
摘要： We introduce zinc oxide (ZnO) functionalized porous gold nanoparticles which exhibit strong second harmonic (SH) emission due to an efficient coupling of localized surface plasmons to ZnO excitons. The nanosponges are perforated with a random network of 10-nm sized ligaments, localizing plasmons in a high density of hot spots. We use a broadband, few-cycle ultrafast laser to probe coherent nonlinear emission from individual bare gold and ZnO-functionalized sponges. While the third harmonic spectrum of the hybrid particles redshifts with respect to that of bare gold sponges, a distinct blueshift is seen in their SH spectra. SH emission around 390 nm, slightly below the ZnO band gap, is enhanced by ten times. We attribute this to doubly-resonant plasmon-exciton interactions: the laser drives nanosponge plasmon hot spot resonances and this locally enhanced field induces two-photon excitation of localized ZnO excitons. This opens a path towards the design of efficient coherent nonlinear optical sources by combining randomly-disordered nanoantennas with semiconductor gain materials.
关键词： exciton-plasmon coupling,Surface plasmons,third harmonic generation,zinc oxide,disordered nanoantennas,plasmon localization,nonlinear optics
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - MoSe <sub/>2</sub> and WSe <sub/>2</sub> Embedded in Bragg-Cavities with High Q-Factors Enabling Strong Exciton-Polariton Coupling in 2D-Systems
摘要： Transition metal dichalcogenides (TMDCs) are semiconducting 2D-materials with a direct bandgap in a range of 1.0 to 2.5 eV. The electronic and optical properties of TMDCs are dominated by strongly bound excitons, suitable for the observation of coupled light-matter interactions in highly resonant cavities. From an application point of view, such cavities must not only provide high Q-factors but must also be robust and reproducible. We report on the fabrication of TMDC-loaded cavities, carried out in an ion-assisted deposition (IAD) process. Mechanically exfoliated MoSe2 and WSe2 monolayer flakes were placed on a sputtered DBR made of SiO2 and TiO2 layers. The second cavity mirror consisting of eight SiO2-TiO2-pairs was deposited directly on the top via IAD, preserving gentle coating conditions to comply with the weak van-der-Waals adhesion of the TMDC flakes. A top-view of a TMDC-loaded part before and after the coating process of the cavity is depicted in Fig. 1(a). Experimental PL measurements with multiple cooling-heating cycles between 5 K and 300 K (shown in Fig. 1(b)), indicate that the process does not damage the TMDC-flakes. A resonance bandwidth of (cid:543)(cid:2019) = 0.16 nm was determined for the cavity, equating into a Q-factor of (cid:1869) = 4683. With PL measurements on a FIB-cut lamella, the presence of pristine, high-quality MoSe2 in the cavity was proven [5]. Further PL measurements showed that the excitons do strongly couple to the cavity mode, verified with Zeeman-splitting of the hybridized polaritonic branches (shown in Fig. 1(c)). The influence of a magnetic field splits and polarizes the hybrid light-matter coupled groundstate, which indicates a polaritonic resonance. The fit to a coupled oscillator model showed a Rabi splitting of about 51 meV and a detuning of about 55 meV corresponding to a |(cid:1850)(cid:2870)|~ 0.13. Based on our findings, we will discuss concrete technical steps, to increase of the optical Q-factor and enhance the exciton linewidth, which will lead to room-temperature strong coupling.
关键词： high Q-factors,exciton-polariton coupling,2D-systems,MoSe2,WSe2,Bragg-Cavities
更新于2025-09-12 10:27:22
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Excitonic complexes in MOCVD-grown InGaAs/GaAs quantum dots emitting at telecom wavelengths
摘要： Hereby, we present a comprehensive experimental and theoretical study of the electronic structure and optical properties of excitonic complexes in strain-engineered InGaAs/GaAs quantum dots (QDs) grown by metalorganic chemical vapor deposition and emitting at the 1.3-μm telecommunication window. Single QD properties have been determined experimentally for a number of nanostructures by means of excitation-power-dependent and polarization-resolved microphotoluminescence and further compared with the results of confined states calculations employing the eight-band k·p theory combined with the configuration interaction method. The origin of excitonic complexes has been exemplarily confirmed based on magneto-optical and correlation spectroscopy study. Understanding the influence of structural parameters and compositions (of QDs themselves as well as in the neighboring strain-reducing layer) allows identification of which of them are crucial to control the emission wavelength to achieve the telecommunication spectral range or to affect binding energies of the fundamental excitonic complexes. The obtained results provide deeper knowledge of control and limitations of the investigated structures in terms of good spectral isolation of individual optical transitions and spatial confinement, which are crucial in view of QD applications in single-photon sources of high purity at telecom wavelengths.
关键词： strain-reducing layer,biexciton,quantum dots,single-photon sources,exciton,telecommunication wavelengths
更新于2025-09-12 10:27:22
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Simultaneous Existence of Confined and Delocalized Vibrational Modes in Colloidal Quantum Dots
摘要： Coupling to phonon modes is a primary mechanism of excitonic dephasing and energy loss in semiconductors. However, low-energy phonons in colloidal quantum dots and their coupling to excitons are poorly understood, since their experimental signatures are weak and usually obscured by unavoidable inhomogeneous broadening of colloidal dot ensembles. We use multi-dimensional coherent spectroscopy at cryogenic temperatures to extract the homogeneous nonlinear optical response of excitons in a CdSe/CdZnS core/shell colloidal quantum dot ensemble. Comparison to simulation provides evidence that the observed lineshapes arise from the co-existence of confined and delocalized vibrational modes, both of which couple strongly to excitons in CdSe/CdZnS colloidal quantum dots.
关键词： multi-dimensional coherent spectroscopy,exciton,colloidal quantum dots,CdSe/CdZnS,phonon modes
更新于2025-09-12 10:27:22