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Strained bubbles in van der Waals heterostructures as local emitters of photoluminescence with adjustable wavelength
摘要： The possibility to tailor photoluminescence (PL) of monolayer transition metal dichalcogenides (TMDCs) using external factors such as strain, doping and external environment is of significant interest for optoelectronic applications. Strain in particular can be exploited as a means to continuously vary the bandgap. Micrometer-scale strain gradients were proposed for creating ‘artificial atoms’ that can utilize the so-called exciton funneling effect and work, for example, as exciton condensers. Here we describe room-temperature PL emitters that naturally occur whenever monolayer TMDC is deposited on an atomically flat substrate. These are hydrocarbon-filled bubbles which provide predictable, localized PL from well-separated submicron areas. Their emission energy is determined by the built-in strain controlled only by the substrate material, such that both the maximum strain and the strain profile are universal for all bubbles on a given substrate, i.e., independent of the bubble size. We show that for bubbles formed by monolayer MoS2, PL can be tuned between 1.72 to 1.81 eV by choosing bulk PtSe2, WS2, MoS2 or graphite as a substrate and its intensity is strongly enhanced by the funneling effect. Strong substrate-dependent quenching of the PL in areas of good contact between MoS2 and the substrate ensures localization of the luminescence to bubbles only; by employing optical reflectivity measurements we identify the mechanisms responsible for the quenching. Given the variety of available monolayer TMDCs and atomically flat substrates and the ease of creating such bubbles, our findings open a venue for making and studying the discussed light-emitting ‘artificial atoms’ that could be used in applications.
关键词： photoluminescence,exciton funneling,monolayer transition metal chalcogenides,excitons,strain engineering
更新于2025-09-19 17:15:36
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Influence of morphology on the blinking mechanisms and the excitonic fine structure of single colloidal nanoplatelets
摘要： Colloidal semiconductor nanoplatelets with a similar electronic structure as quantum wells have recently emerged as exciting materials for optoelectronic applications. Here we investigate how morphology affects important photoluminescence properties of single CdSe and core/shell CdSe/CdZnS nanoplatelets. By analyzing photoluminescence intensity-lifetime correlation and second-order photon correlation results, we demonstrate that, irrespective of the morphology, Auger recombination plays only a minor role in dictating the blinking behavior of the nanoplatelets. We find that a rough shell induces additional non-radiative channels presumably related to defects or traps of an imperfect shell. Furthermore, polarization-resolved spectroscopy analysis reveals exciton fine-structure splitting of the order of several tens of meV in rough-shell nanoplatelets at room temperature, which is attributed to exciton localization and is substantiated by theoretical calculations taking into account the nanoplatelet shape and electron–hole exchange interaction.
关键词： exciton fine structure,photoluminescence,nanoplatelets,blinking,Auger recombination
更新于2025-09-19 17:15:36
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Effects of near-field electromagnetic coupling in dimers of nanoparticles with a silver core and a J-aggregate dye shell
摘要： We report a theoretical study of the plasmon – exciton coupling effect on the absorption spectra of pairs of closely spaced double-layer hybrid nanoparticles consisting of a metallic core and a J-aggregate dye shell. The effect of frequency conversion of plasmonic lines due to the near-field interaction between plasmons and Frenkel excitons of the organic shell is demonstrated. The effect leads to the appearance of additional spectral lines in the long-wavelength part of the spectrum of the system of hybrid particles. The shapes and the relative intensities of the additional lines exactly reproduce the specific features of the original spectrum of plasmonic absorption bands in uncoated metallic nanoparticles. The discovered phenomenon can be used to design new types of high-sensitivity nanosensors, based on plasmon – exciton effects and principles of near-field optics.
关键词： near-field electromagnetic coupling,nanophotonics,Frenkel excitons,dimers of metalorganic nanoparticles,plasmon – exciton interaction,molecular J-aggregates,localised plasmons,absorption spectra
更新于2025-09-19 17:15:36
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Binding energy of an exciton in a GaN/AlN nanodot: Role of size and external electric field
摘要： We report the impact of an external electric field on the energy spectrum of an exciton inside a spherical shaped GaN/AlN core/shell nanodot. The modulation of the confined exciton lowest state energy by the nanodot size is also treated. Our theoretical approach, based on a variational calculation, predicts a remarkable decrease in the exciton's energy when the electric field is switched on. Furthermore, our investigation shows that for a fixed nanodot size, the energy redshift is a unique function of the external electric field strength. On the other hand, it was observed that as the nanodot size increases the lowest exciton energy decreases and vice versa.
关键词： electric field,core/shell materials,nanostructures,quantum dots,exciton
更新于2025-09-19 17:15:36
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Many-body States Description of Single-molecule Electroluminescence Driven by Scanning Tunneling Microscope
摘要： Electron transport and optical properties of a single molecule in contact with conductive materials have attracted considerable attention owing to their scientific importance and potential applications. With recent progresses of experimental techniques, especially by the virtue of scanning tunneling microscope (STM)-induced light emission, where the tunneling current of the STM is used as an atomic-scale source for induction of light emission from a single molecule, it becomes possible to investigate single-molecule properties at sub-nanometer spacial resolution. Despite extensive experimental studies, the microscopic mechanism of electronic excitation of a single molecule in STM-induced light emission is yet to be clarified. Here we present a formulation of single-molecule electroluminescence driven by electron transfer between a molecule and metal electrodes based on a many-body state representation of the molecule. The effects of intra-molecular Coulomb interaction on conductance and luminescence spectra are investigated using the nonequilibrium Hubbard Green's function technique combined with first-principles calculations. We compare simulation results with experimental data and find that the intra-molecular Coulomb interaction is crucial for reproducing recent experiments for a single phthalocyanine molecule. The developed theory provides a unified description of both electron-transport and optical properties of a single molecule in contact with metal electrodes driven out of equilibrium, and thereby it contributes to a microscopic understanding of optoelectronic conversion in single molecules on solid surfaces and in nanometer-scale junctions.
关键词： Single molecule luminescence,exciton formation,nonequilibrium Hubbard Green's function technique,time-dependent density functional theory (TDDFT),scanning tunneling microscope-induced light emission,Vibronic interaction
更新于2025-09-19 17:15:36
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A cost-effective realization of multimode exciton-polaritons in single-crystalline microplates of a layered metal-organic framework
摘要： We report the observation of multimode exciton-polaritons in single-crystalline microplates of a two-dimensional (2D) layered Metal-Organic Framework (MOF), which can be synthesized through a facile solvothermal approach, thereby eliminating all fabrication complexities usually involved in the construction of polariton cavities. With a combination of experiments and theoretical modelling, we have found that the exciton-polaritons are formed at room temperature, as a result of a strong coupling between Fabry-Perot cavity modes formed inherently by two parallel surfaces of a microplate and Frenkel excitons provided by the 2D layers of dye molecular linkers in the MOF. Flexibility in rational selection of dye linkers for synthesizing such MOFs renders a large-scale, low-cost production of solid-state, micro- exciton-polaritonic devices operating in the visible and near infrared (NIR) range. Our work introduces the MOF as a new class of potential materials to explore polariton-related quantum phenomena in a cost-effective manner.
关键词： Strong Coupling,Exciton-Polaritons,Multimode Coupling,Metal-Organic Framework,Angle-Resolved Reflectivity,Rhodamine B
更新于2025-09-19 17:15:36
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Embedded two dimensional perovskite nanoplatelets with air-stable luminescence
摘要： Two-dimensional (2D) perovskites represent a class of promising nanostructures for optoelectronic applications owing to their giant oscillator strength transition of excitons and high luminescence. However, major challenges lie in the surface ligand engineering and ambient stability. Here we show that air-stable quasi-2D CsPbBr3 nanoplatelets (NPLs) can be formed in the matrix of Cs4PbBr6 nanosheets by reducing the thickness of Cs4PbBr6 to ~7.6 nm, the scale comparable to the exciton Bohr radius of CsPbBr3. The 2D behavior of excitons is evidenced by the linear increase of radiative lifetime with increasing temperature. Moreover, the wide bandgap Cs4PbBr6 plays roles of surface passivation and protection, which leads to good photoluminescence properties without photo-bleaching effect and with ambient stability for over one month. Our work demonstrates a unique quasi-2D heterostructure of perovskite nanomaterials which may either serve as a workbench for studying the exciton recombination dynamics or find application in high performance optoelectronic devices.
关键词： two dimensional exciton,heterostructure,luminescence,lead halide perovskite
更新于2025-09-19 17:15:36
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Optical Sensing Properties of ZnO Nanoparticles Prepared by Spray Pyrolysis
摘要： We studied the optical sensing properties of ZnO nanoparticles prepared by spray pyrolysis. To investigate their optical sensing performance, we incubated peptides on ZnO nanoparticles. The photoluminescence (PL) peak intensity of peptides on the ZnO nanoparticles was higher than that of peptides on the ZnO film or on the glass plate. This observed PL enhancement is attributed to the optical confinement of ZnO nanoparticles. The low-temperature spectra displayed a strong exciton emission peak with multiple sidebands, attributed to the bound exciton and its longitudinal optical phonon sidebands. The strong exciton emission is thought to be the combined effect of optical confinement due to the nanoparticle geometry, reduction of defect emission by thermal annealing, and reduction of non-radiative relaxation at low temperatures.
关键词： Exciton,ZnO Nanoparticles,Photoluminescence,Peptide,Optical Sensing
更新于2025-09-19 17:15:36
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Excitonic properties in an asymmetric quantum dot nanostructure under combined influence of temperature and lateral hydrostatic pressure
摘要： Simultaneous influences of temperature and lateral hydrostatic pressure combined to axial asymmetric confinement potential and size effects on the behavior of the exciton in 0D (cid:1833)(cid:1853)(cid:1827)(cid:1871)/(cid:1833)(cid:1853)((cid:2869)(cid:2879)(cid:3051)(cid:3285))Al((cid:2934)(cid:3168)) asymmetric cylindrical quantum dot (QD) nanostructure are investigated. Our calculations are performed in the framework of the effective mass approximation by using a variational method with a robust trial wave function through taking into account the dependence of exciton properties on the QD sizes, the axial asymmetric confinement potential, the temperature and the pressure. Variation of the excitonic binding energy, photoluminescence energy transition and band gap energy are discussed according to temperature and hydrostatic pressure for different confinement regimes and various potential wells. Our numerical findings show that the applied pressure favors the attraction between electron and hole while the temperature tends to decrease the exciton binding energy. Furthermore, the photoluminescence energy is decreasing function of the temperature and increasing function of the pressure. The opposing influences caused by temperature and lateral hydrostatic pressure with contribution of variation of axial asymmetric confinement potential reveal a significant practical interest and offer an alternative manner to the tuning of the excitonic transition in optoelectronic devices.
关键词： Exciton,Temperature,Asymmetric potential,Quantum dots,Hydrostatic pressure
更新于2025-09-19 17:13:59
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Complete state tomography of a quantum dot spin qubit
摘要： Semiconductor quantum dots are probably the preferred choice for interfacing anchored matter spin qubits and flying photonic qubits. While full tomography of a flying qubit or light polarization is, in general, straightforward, matter spin tomography is a challenging and resource-consuming task. Here we present an all-optical method for conducting full tomography of quantum dot confined spins. Our method is applicable for electronic spin configurations such as the conduction-band electron and the valence-band hole and for electron-hole pairs such as the bright and dark excitons. We excite the spin qubit using a short, resonantly tuned, polarized optical pulse, which coherently converts the qubit to an excited qubit that decays by emitting a polarized single photon. We perform the tomography by using two different orthogonal, linearly polarized excitations, followed by time-resolved measurements of the degree of circular polarization of the emitted light from the decaying excited qubit. We demonstrate our method on the dark exciton spin state with a fidelity of 0.94, mainly limited by the accuracy of our polarization analyzers.
关键词： spin qubits,tomography,optical methods,dark exciton,quantum dots
更新于2025-09-19 17:13:59