China
Africa
Explore chapters and articles related to this topic
Excitons in Quantum Confined Systems
Published in Vladimir I. Gavrilenko, Optics of Nanomaterials, 2019
The biexciton binding energy depends strongly on the constituent exciton states in all nanoparticle sizes. For CdS0.6Se0.4 nanocrystals with R ≃ 0.75aB, the biexciton energies are 1.32 EB, 4.45EB, and 5.95 EB for |1Se1Sh; 1Se1Sh〉, |1Se1Sh;1Pe1Ph〉, |1Se 1Sh;1Se 1Ph〉 states, respectively. The Rydberg energy EB is estimated to be ∼ 17.2 meV based on the value of aB = 40 Å. The biexciton binding energy increases with asymmetric feature in the composite exciton states and the biexciton states because symmetric states induce a compensation between Coulomb attraction and repulsion and have no net Coulomb interaction. The theoretical calculations are in a good agreement with the observed experimental results, showing an enhancement of photoinduced absorption of B band and a gradual redshift of A1 band as the |1Se1Sh〉, |1Pe1Ph〉, and |1Se1Ph〉 excitons are excited by the pump beam.
Electromagnetically Induced Transparency in Semiconductor Quantum Wells
Published in Kong-Thon Tsen, and Nanostructures, 2018
While one can attempt to adapt and extend concepts and techniques developed in an atomic system to an excitonic system, a fundamental issue for manipulating excitonic quantum coherences is how many-body Coulomb interactions between excitons, which are inherent in an excitonic system but are absent in simple atomic systems, affect the creation, evolution, and manipulation of these coherences. We have taken advantage of the many-body Coulomb interactions between excitons and developed EIT schemes that are based on the use of exciton spin coherence and biexciton coherence in GaAs QW structures. Exciton spin coherence is a coherent superposition of the exciton spin states. Biexciton coherence is a coherent superposition of the crystal ground state and a bound state of two excitons. Both of these coherences arise from Coulomb interactions between excitons and have no counterparts in independent atomic systems. In this section, we discuss EIT arising from the exciton spin coherence. Experimental results presented in this section were all obtained in a 10-nm GaAs QW.
Nonlinear Optical Properties of Semiconductors, Principles, and Applications
Published in Inamuddin, Mohd Imran Ahamed, Rajender Boddula, Tariq Altalhi, Optical Properties and Applications of Semiconductors, 2023
Muhammad Rizwan, Aleena Shoukat, Asma Ayub, Iqra Ilyas, Ambreen Usman, Seerat Fatima
In the intermediate density section, the process of the interactions among excitons starts. In this, the collisions may be elastic or inelastic or combined to build a new excitonic state named biexciton. These scattering processes of biexciton state with interaction of photon give rise to the PEONL such as excitation-induced absorption, or new emission band arrival, or exciton resonance's collision broadening (Broser and Gutowski 1988; Hönerlage et al. 1985).
Stark shift and exciton binding energy in parabolic quantum dots: hydrostatic pressure, temperature, and electric field effects
Published in Philosophical Magazine, 2021
O. Mommadi, A. El Moussaouy, M. El Hadi, M. Chnafi, Y. M. Meziani, C. A. Duque
The influence of EF on the exciton confined in nanostructure systems becomes the main topic of several theoretical and experimental investigations. Oukkeroum et al. [48] have studied the ground state EBE and the exciton related Stark shift in PbS quantum disk by examining a 2D oscillator strength under the contribution of lateral EF and geometrical confinement. Their results show that the EBE and Stark shifts depend strongly on the disk dimension in both longitudinal and axial directions. Ulrich et al. [49] have studied the spontaneous emission characteristics of a single self-assembled (In,Ga)As/GaAs QD under the effect of EF strength. They have observed that the Stark effects of the neutral exciton, biexciton, and trionic have similar behaviours. Recently, the polarisability and the photoionisation cross-section of individual dopant in spherical AlAs/GaAs core/shell QD have been investigated, under external EF and HP influences, by M'zerd et al. [50]. They have obtained that the energy shift under EF becomes even more significant for the impurity located at the core/shell center. Furthermore, the donor BE and the polarisability decrease with enhancing the EF. Also, it is observed that the intensity of electric polarisability decreases more rapidly when considering stress effects. The action of EF on exciton immersed in cylindrical nanosystem with parabolic confinement potential is recently investigated [51]. It is found that the BE and its polaronic shift of exciton diminish with electric field strength.
Bayesian spectroscopy of synthesized soft X-ray absorption spectra showing magnetic circular dichroism at the Ni-L3, -L2 edges
Published in Science and Technology of Advanced Materials: Methods, 2021
Taiga Yamasaki, Kazunori Iwamitsu, Hiroyuki Kumazoe, Masato Okada, Masaichiro Mizumaki, Ichiro Akai
Bayesian spectroscopy [1,2] is a data-driven science approach of that we apply Bayesian inference [3] onto spectral analysis to achieve highly challenging spectral decomposition. In the Bayesian inference of the data-driven science [4], Bayes’ theorem [3] is applied to the joint probability of causes and results in the causality, and evaluation of posterior probability distributions for causes becomes available based on the resultant data. Such evaluation is one of major advantages in Bayesian spectroscopy and it makes possible to provide a statistical guarantee for a particularly-difficult spectral decomposition. Such advantage has been illustrated by the Bayesian spectroscopy of admixed photoluminescence spectra with exciton, biexciton and electron-hole droplet (EHD) states in a highly-excited GaAs/AlAs type-II superlattice [5], where we have demonstrated that the EHD state becomes stable from the evaluation of the posterior probability distributions for a chemical potential of the EHD, an energy of excitonic system and their effective temperature [6].
Atomistic tight-binding computations of the structural and optical properties of CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals
Published in Philosophical Magazine, 2018
Finally, the splitting of the ground excitonic states in CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals is demonstrated numerically. The excitonic splitting is intrinsically induced by the electron–hole exchange interaction. Using the configuration interaction (CI) description of this computational task, all possible determinants that can be constructed from 12 lowest-energy electron and hole states, with consideration of the spin, are included in the two-body Hamiltonian (Hex). Stokes shift and fine-structure splitting are exemplified under different internal shell types and external ZnS growth shell thicknesses in Figures 10 and 11, respectively. To theoretically describe the natures of the Stokes shift and fine-structure splitting, the overlap of the electron–hole wave function is the main candidate. [58,59] In the presence of an external ZnS shell, the Stokes shift increases, whereas the fine-structure splitting decreases. The resulting calculations demonstrate that the Stokes shift and the fine-structure splitting are gradually reduced with increasing external ZnS growth shell thickness, which corresponds to the reduced ground electron–hole wave function overlaps. In terms of the internal shell types, the Stokes shift and fine-structure splitting of CdTe/CdS/ZnS core/shell/shell nanocrystals are clearly greater than those of CdTe/CdS/ZnS core/shell/shell nanocrystals. This is due to the nature of the ground electron–hole wave function overlaps. It is anticipated that CdTe/CdSe/ZnS core/shell/shell nanocrystal with a dense coated shell is the best candidate for being a source of entangled photon pairs based on the biexciton (XX)–exciton (X)–ground (O) state cascade process [60]. From the theoretical point of view, the atomistic tight-binding calculations, which capture realistic nanostructures, are capable of qualitatively predicting the details of the Stokes shift and the fine-structure splitting in CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals.