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Ultrafast dynamics in van der Waals heterostructures
摘要： Van der Waals heterostructures are synthetic quantum materials composed of stacks of atomically thin two-dimensional (2D) layers. Because the electrons in the atomically thin 2D layers are exposed to layer-to-layer coupling, the properties of van der Waals heterostructures are defined not only by the constituent monolayers, but also by the interactions between the layers. Many fascinating electrical, optical and magnetic properties have recently been reported in different types of van der Waals heterostructures. In this Review, we focus on unique excited-state dynamics in transition metal dichalcogenide (TMDC) heterostructures. TMDC monolayers are the most widely studied 2D semiconductors, featuring prominent exciton states and accessibility to the valley degree of freedom. Many TMDC heterostructures are characterized by a staggered band alignment. This band alignment has profound effects on the evolution of the excited states in heterostructures, including ultrafast charge transfer between the layers, the formation of interlayer excitons, and the existence of long-lived spin and valley polarization in resident carriers. Here we review recent experimental and theoretical efforts to elucidate electron dynamics in TMDC heterostructures, extending from timescales of femtoseconds to microseconds, and comment on the relevance of these effects for potential applications in optoelectronic, valleytronic and spintronic devices.
关键词： spin and valley polarization,charge transfer,valleytronic,transition metal dichalcogenide,Van der Waals heterostructures,excited-state dynamics,spintronic devices,interlayer excitons,optoelectronic
更新于2025-09-23 15:21:01
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Opportunities and challenges of interlayer exciton control and manipulation
摘要： Advances in van der Waals heterostructures allow the control of interlayer excitons by electrical and other means, promising exciting opportunities for high-temperature exciton condensation and valley–spin optoelectronics.
关键词： TMD bilayers,exciton condensation,van der Waals heterostructures,valley–spin optoelectronics,interlayer excitons
更新于2025-09-23 15:21:01
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Mn-doped 2D Sn-based perovskites with energy transfer from self-trapped excitons to dopants for warm white light-emitting diodes
摘要： Mn-doped 2D perovskite powders are promising phosphors for warm white light-emitting diodes (LEDs). However, it remains a challenge to solve the problem of lead toxicity and improve photoluminescence quantum yields (PLQYs). Here, we have successfully prepared Mn-doped 2D Sn-based perovskite materials ((C8H17NH2)2Sn1-xMnxBr4). The PLQYs of (C8H17NH2)2Sn1-xMnxBr4 (x = 0.26) powders reach up to 42%. The as-prepared (C8H17NH2)2Sn1-xMnxBr4 exhibit a single broad photoluminescence (PL) band, differing from the dual peaks of Mn-doped lead halide perovskite quantum dots. Theoretical conclusions and experimental results show the competitive relationship between self-trapped excitons (STEs) emission from the host crystal and dopant Mn d-d transition emission. With Mn dopant concentration increasing, the PL spectra exhibit red shifts and the full width at half-maximum (FWHM) turns larger, which is constructive for warm white LEDs. The fabricated warm white LEDs based on (C8H17NH2)2Sn1-xMnxBr4 show warm white light correlated color temperature (CCT, 3542 K) and high color-rendering index (Ra, 88.12). Our work provides new possibilities for optoelectronic devices based on lead-free perovskite materials.
关键词： self-trapped excitons,Mn-doped,photoluminescence quantum yields,2D Sn-based perovskites,warm white light-emitting diodes
更新于2025-09-23 15:21:01
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Interaction of Rydberg excitons in cuprous oxide with phonons and photons: optical linewidth and polariton effect
摘要： We demonstrate that the optical linewidth of Rydberg excitons in Cu2O can be completely explained by scattering with acoustical and optical phonons, whereby the dominant contributions stems from the non-polar optical 3G- and 5G- modes. The consequences for the observation of polariton effects are discussed. We find that an anti-crossing of photon and exciton dispersions exists only for states with main quantum numbers n > 28, so polariton effects do not play any role in the experiments reported up to now.
关键词： polaritons,phonon scattering,Rydberg excitons,cuprous oxide
更新于2025-09-23 15:21:01
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A Pentacene-based Nanotube Displaying Enriched Electro/Photochemical Activities
摘要： We report the first synthesis of a pentacene-based nanotube displaying a tubular conformation in solution. The product possesses a triangular prismatic structure with three pentacene chromophores connected by a rigid, triangular backbone. Steady-state and time-resolved spectroscopic analyses revealed that the nanotube exhibits enriched electro/photochemical activities due to the close proximity of the three pentacene chromophores, which allows for efficient intramolecular singlet fission and long-lived triplet excitons.
关键词： photochemistry,pentacene,singlet fission,nanotube,triplet excitons,electrochemistry
更新于2025-09-23 15:21:01
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Long coherent dynamics of localized excitons in (In,Ga)N/GaN quantum wells
摘要： We study the coherent dynamics of localized excitons in 100 periods of 2.5-nm-thick (In,Ga)N/GaN quantum wells with 7.5% indium concentration, measured with spectroscopic resolution through two-pulse and three-pulse photon echoes at the temperature of 1.5 K. A long-lived coherent exciton dynamics is observed in the (In,Ga)N quantum wells: When the laser photon energy is tuned across the 43-meV-wide inhomogeneously broadened resonance line, the coherence time T2 varies between 45 and 255 ps, increasing with stronger exciton localization. The corresponding narrow homogeneous linewidths ranging from 5.2 to 29 μeV as well as the relatively weak exciton-phonon interaction (0.7 μeV/K) confirm a strong, quantum-dot-like exciton localization in a static disordered potential inside the (In,Ga)N quantum well layers.
关键词： localized excitons,photon echoes,exciton-phonon interaction,coherent dynamics,(In,Ga)N/GaN quantum wells
更新于2025-09-23 15:21:01
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Bayesian Spectroscopy on Polarization Dependent Photoluminescence Spectra of Doubly-Split Excitons in a Cu <sub/>2</sub> O Thin-Crystal Sandwiched by MgO Substrates
摘要： By using Bayesian spectroscopy, we studied polarization dependence of photoluminescence (PL) spectra in doubly-split 1S yellow ortho-excitons in a Cu2O thin-crystal recrystallized in a small gap between paired MgO substrates. In these thin-crystals, biaxial stresses are expected to be involved due to a small lattice mismatch between Cu2O and MgO. Under a planar-isotropic biaxial stress, the cubic symmetry degrades to the tetragonal one in Cu2O, and subsequently, the ortho-exciton state splits into two states having different symmetries. Consequently, the resonant PL intensities of the doubly-split ortho-excitons are expected to show different polarization dependencies. To elucidate such biaxial stress effect, we measured polarization dependence of the PL spectra at 4.2 K. Although resonant weak PL bands of the doubly-split exciton states and their intense phonon sidebands co-exist, we succeeded in decomposing to the respective spectral components by the Bayesian spectroscopy with a replica exchange Monte Carlo algorithm. As a result, it is found that the resonant PL band appearing on higher energy side shows hardly polarization dependence, whereas the resonant PL band appearing on lower energy side is further weak and shows noticeable polarization dependence. These results can be explained by the selection rule and polarization dependences on the transition matrix elements of quadrupole transitions of the doubly-split ortho-exciton states, and it clearly shows that the crystal symmetry degrades to D4h by the isotropic biaxial stress involved in the Cu2O thin-crystals.
关键词： Bayesian spectroscopy,excitons,biaxial stress effect,polarization dependence,Cu2O
更新于2025-09-23 15:21:01
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Quantum Dots - Theory and Applications || Theory of Excitons and Excitonic Quasimolecules Formed from Spatially Separated Electrons and Holes in Quasi-Zero- Dimensional Nanostructures
摘要： The theory of an exciton formed from a spatially separated electron and a hole is developed within the framework of the modified effective mass method. The effect of significantly increasing the exciton binding energy in quantum dots of zinc selenide, synthesized in a borosilicate glass matrix and relative to that in a zinc selenide single crystal is revealed. It is shown that the short-wavelength shift of the peak of the low-temperature luminescence spectrum of samples containing zinc selenide quantum dots, observed under experimental conditions, is caused by quantum confinement of the ground-state energy of the exciton with a spatially separated electron and hole. A review devoted to the theory of excitonic quasimolecules (biexcitons) (made up of spatially separated electrons and holes) in a nanosystem that consists of ZnSe quantum dots synthesized in a borosilicate glass matrix is developed within the context of the modified effective mass approximation. It is shown that biexciton (exciton quasimolecule) formation has a threshold character and is possible in a nanosystem, where the spacing between quantum dots' surfaces is larger than a certain critical arrangement. An analogy of the spectroscopy of the electronic states of superatoms (or artificial atoms) and individual alkali metal atoms theoretically predicted a new artificial atom that was similar to the new alkali metal atom.
关键词： excitonic quasimolecules,Excitons,superatoms,spatially separated electrons and holes,exciton binding energy,quantum dots
更新于2025-09-23 15:19:57
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Resonance fluorescence of a single semiconductor quantum dot: the impact of a fluctuating electrostatic environment
摘要： Semiconductor quantum dots are very efficient sources of single and highly indistinguishable photons. These properties rely on the possibility to coherently control the system at the single spin level. At this ultimate level of control, the quantum dot becomes a very sensitive probe of its solid-state environment and any interaction turns into a dephasing process that alters its coherence properties. In this topical review, we give an overview of the issue of charge noise which remains one of the main dephasing mechanisms to overcome. This phenomenon which strongly depends on sample preparation, originates from a fluctuating electrostatic landscape around the quantum dots and renders a unified description quite awkward. We present the common characteristic features induced by charge noise that have been observed in the resonant fluorescence experiments of single quantum dots and discuss the different approaches that have been proposed in the literature to circumvent this problem.
关键词： quantum dots,quantum coherence,optical properties,resonance fluorescence,excitons,III–V semiconductors
更新于2025-09-23 15:19:57
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Non-perturbative multiphoton excitation studies in an excitonic coupled quantum well system using high-intensity THz laser fields
摘要： Multiphoton excitations and nonlinear optical properties of exciton states in GaAs/AlxGa1?xAs coupled quantum well structure have been theoretically investigated under the influence of a time-varying high-intensity terahertz (THz) laser field. Non-perturbative Floquet theory is employed to solve the time-dependent equation of motion for the laser-driven excitonic quantum well system. The response to the field parameters, such as intensity and frequency of the laser electric field on the state populations, can be used in various optical semiconductor device applications, such as photodetectors, sensors, all-optical switches, and terahertz emitters.
关键词： laser,multiphoton,quantum well,excitons,Floquet,terahertz,non-perturbative
更新于2025-09-23 15:19:57