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Photoassociative spectroscopy of a halo molecule in
摘要： We present two-photon photoassociation to the least-bound vibrational level of the X 1Σ+g electronic ground state of the 86Sr2 dimer and measure a binding energy of Eb = ?83.00(7)(20) kHz. Because of the very small binding energy, this is a halo state corresponding to the scattering resonance for two 86Sr atoms at low temperature. The measured binding energy, combined with universal theory for a very weakly bound state on a potential that asymptotes to a van der Waals form, is used to determine an s-wave scattering length a = 810.6(3)(9) a0, which is consistent with, but substantially more accurate than, the previously determined a = 798(12) a0 found from mass scaling and precision spectroscopy of other Sr isotopes. For the intermediate state, we use a bound level on the metastable 1S0-3P1 potential. Large sensitivity of the dimer binding energy to light near resonant with the bound-bound transition to the intermediate state suggests that 86Sr has great promise for manipulating atom interactions optically and probing naturally occurring Efimov states.
关键词： scattering length,binding energy,Efimov states,photoassociation,halo molecule,86Sr
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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[IEEE 2018 IEEE 8th International Conference Nanomaterials: Application & Properties (NAP) - Zatoka, Ukraine (2018.9.9-2018.9.14)] 2018 IEEE 8th International Conference Nanomaterials: Application & Properties (NAP) - Time-Resolved Photoluminescence of CdSe/CdS/CdZnS Quantum Dots
摘要： We demonstrate that in the study of time-resolved photoluminescence the signatures of biexcitons in QDs can manifest themselves even when the system is excited by long laser pulses with their duration of the order of several tens of picoseconds. To describe the results of our measurements we propose an elegant theoretical model. It is based on the introduction of auxiliary sources in the rate equations. The parameters of the sources are determined by fitting the analytical solution of these equations that describes the full emission of the system to the experimental results obtained. Having found the parameters of the auxiliary sources we can determine the temporal dependences of the radiation from excitons and biexcitons separately. We find the spectral positions of the exciton and biexciton emission bands, their widths, and the biexciton binding energy.
关键词： quantum dots,photoluminescence,exciton,rate equations,binding energy,biexciton
更新于2025-09-23 15:19:57
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Effects of built-in electric field on donor binding energy in InGaN/ZnSnN2 quantum well structures
摘要： InxGa1?xN/ZnSnN2 quantum well structures are studied in terms of a binding energy of a donor atom. 1s and 2p± impurity states are considered. The Schr?dinger’s and Poisson’s equations are solved self-consistently. A hydrogenic type wave function to represent each impurity state is assumed. The calculations include band-bending in the potential energy profile introduced by the built-in electric field existing along the structures. The binding energy and the energy of the transition between the impurity states are represented as a function of the quantum well width, the donor position, and the indium concentration. An external magnetic field up to 10 T is included into the calculations to compute the Zeeman splitting. The maximum value of the transition energy is around 30 meV (nearly 7.3 THz) which occurs in a 15-? In0.3Ga0.7N/ZnSnN2 quantum well. Being strong, the built-in electric field makes the transition energy drop quickly with the decreasing well width. For the same reason, the energy curves are found to be highly asymmetric function of the donor position around the well center. Compared to the bulk value, the transition energy in the quantum well structures enhances nearly two-fold.
关键词： Binding energy,ZnSnN2,Impurity,Quantum well,Donor,GaN
更新于2025-09-19 17:15:36
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Atypical Defect-Mediated Photoluminescence and Resonance Raman Spectroscopy of Monolayer WS2
摘要： Defects play an indispensable role in tuning the optical properties of two-dimensional(2D) materials. Herein, we study the influence of defects on the photoluminescence (PL) and resonance Raman spectra of as-grown monolayer(1L) WS2. Increasing the density of defects significantly lowers the excitonic binding energy by up to 110 meV. These defect-modified excitonic binding energies in1L-WS2 strongly mediate the Raman resonance condition, resulting in unexpected Raman intensity variations in the LA(M), 2LA(M) and phonon modes. The sample with the highest density of defects exhibits an almost temperature independent resonance in different Raman modes at low temperature, while the samples with low densities of defects exhibit clear resonance with decreasing temperature. This study will further increase our understanding of the role of defects in resonance Raman spectroscopy and of the phonon-exciton interaction in 1L-WS2.
关键词： photoluminescence,defects,excitonic binding energy,resonance Raman spectroscopy,monolayer WS2
更新于2025-09-19 17:15:36
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Binding energies and photoionization cross-sections of donor impurities in GaN/AlxGa1a??xN spherical quantum dot under hydrostatic pressure
摘要： In this paper, the binding energy and photoionization cross-section of donor impurity state in GaN/AlxGa1?xN quantum dot structure are studied theoretically by using variational method. The variation of binding energy and photoionization cross-section with core and shell sizes at di?erent impurity locations under hydrostatic pressure is calculated numerically. The results show that the binding energy decreases monotonously with the core size at di?erent impurity locations for GaN/AlxGa1?xN core/shell quantum dot. In contrast, for the inverted core/shell quantum dot, the binding energy exhibits di?erent trends with the increase of core size at di?erent impurity locations. But the binding energy decreases monotonically with the shell size for both of them. Moreover, when the photon energy is approximately equal to the donor binding energy, the peak of the photoionization cross-section appears. There will be di?erent peak shifts under di?erent conditions, and its peak intensity increases with the increase of core and shell sizes. When the hydrostatic pressure is applied, the binding energy and the peak strength of the photoionization cross-section increase with the increase of the pressure.
关键词： hydrostatic pressure,Spherical quantum dot,binding energy,photoionization cross-section
更新于2025-09-19 17:13:59
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Temperature effect on the binding energy and the diamagnetic susceptibility of a magneto-donor in Cylindrical Quantum Dot (GaAs/GaAlAs)
摘要： In this work, the effect of the temperature on the binding energy and the diamagnetic susceptibility of a shallow magneto-donor confined to move in a cylindrical quantum dot made out of GaAs/GaAlAs is studied within the effective mass approximation. We describe the quantum confinement by an infinite deep potential. The results show that when the temperature or the magnetic field increases, (i) the binding energy increases and (ii) the absolute value of the diamagnetic susceptibility decreases. Its effects depend strongly on the size of the CQD.
关键词： GaAs/GaAlAs,temperature effect,binding energy,cylindrical quantum dot,diamagnetic susceptibility,magneto-donor
更新于2025-09-19 17:13:59
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Understanding the excitation wavelength dependent spectral shift and large exciton binding energy of tungsten disulfide quantum dots and its interaction with single-walled carbon nanotubes
摘要： Herein, we investigate the origin of excitation wavelength dependent spectral features and high fluorescence quantum yield in fluorescent 2D tungsten disulfide (WS2) quantum dots (QDs) of average size 2.4 nm. The as-prepared WS2 QDs possess high optical bandgap and reasonably high fluorescence quantum yield ~15.4% in the green region without any functionalization. The broad photoluminescence (PL) spectrum consists of multiple peaks owing to emissions from excitonic transitions and surface defect-related transitions. The excitation wavelength-dependent spectral redshift and narrowing of line shape in the PL peak are analyzed carefully, and it is attributed to the selective excitation/recombination of carriers from different energy levels. The temperature-dependent PL analysis yields an exciton binding energy of ~301 meV in the QDs. Furthermore, we study the interaction between fluorescent WS2 QDs and single-walled carbon nanotubes (SWCNTs) and explore the mechanism of systematic quenching of PL of QDs by SWCNTs. The nature of the Stern–Volmer plot is found to be linear, and the time-resolved fluorescence measurements reveal that the quenching follows primarily the static behavior. Our study further reveals that defect sites in SWCNTs primarily act as the binding sites for WS2 QDs and form non-fluorescent complexes for effective quenching of the PL. The strong interaction between the WS2 QDs and the SWCNTs is evidenced from the spectral shift in the X-ray photoelectron spectroscopy and Raman peaks. Our study reveals the origin of excitation wavelength dependent PL emission from WS2 QDs and the nature of the interaction between WS2 QDs and SWCNTs, which are important for their applications in biomedical imaging and sensing, such as surface-enhanced Raman scattering, etc.
关键词： WS2 quantum dots,Fluorescence quenching,Defects,Carbon nanotubes,Exciton binding energy
更新于2025-09-16 10:30:52
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Electrons in Solids (Mesoscopics, Photonics, Quantum Computing, Correlations, Topology) || 4. Correlated electrons in complex transition metal oxides
摘要： In the previous chapters of this book, we have discussed the consequences of quantum mechanics on the properties of solid state electrons mostly on the single or two particle level. This revealed the important influence of the phase of the electronic wave functions in mesoscopic electronic transport and a general understanding of the optical properties of solids, where the interaction between the electrons led only to relatively simple modifications such as the excitonic binding energy ERyd,X or the dielectric constant of the material ε. In addition, we have learned how to gain an unprecedented control of the quantum mechanical properties, including the dynamics, for single-electron and two-electron systems in spin qubits or in many-particle states in superconducting qubits. There, the electron-electron interaction was mostly used as an exchange coupling or as a classical repulsive energy for read-out.
关键词： spin qubits,electron-electron interaction,mesoscopic electronic transport,excitonic binding energy,superconducting qubits,dielectric constant,solid state electrons,quantum mechanics,optical properties of solids
更新于2025-09-16 10:30:52
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Exciton states in InGaAsP/InP core–shell quantum dots under an external electric field
摘要： The effect of an external electric field on the exciton states of InGaAsP/InP core–shell quantum dots is investigated through the variational method. The effect of the shell thickness, core radius, electric field strength, and material components on the exciton states are analyzed in detail. The numerical results show that the electron and hole energies decrease as the shell thickness or core radius is increased. The Bohr radius is a nonmonotonic function of the shell thickness or core radius, and the change of the exciton binding energy is nonlinear as the shell thickness or core radius is increased. With increasing electric field strength, the Bohr radius increases while the exciton binding energy decreases. The exciton binding energy decreases (increases) as the Ga (As) component is increased.
关键词： Electric field,Core–shell quantum dot,Exciton binding energy
更新于2025-09-16 10:30:52