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An attempt has been made to examine the energetic properties of M center diffusion, excitons near M²⁺, M⁺, M, M^- and M^2- centers and adsorptivity of atomic H and He over defect free and defect containing surfaces of LiH using an ab initio embedded cluster method at the Hatrtree–Fock approximation and Moller–Plesset second order perturbation correction. The results confirm the following, (1) the calculated barriers to diffusion of M center in its lowest triplet excited state is always greater than those in its singlet ground state; (2) the triplet M center is not produced directly by optical processes, but, indirectly by thermal diffusion; (3) the exclusive dependence of exciton bands and the nonexclusive dependence of band gaps on the defect charge; (4) surface relaxation is not more important than bulk relaxation; (5) the M center changes the nature of H adsorption from physical adsorption to chemical adsorption; (6) bulk or surface M^2- changes the nature of LiH from an insulator to a semiconductor; (7) as M center is introduced, the HOMO and LUMO levels of the substrate shift to higher energies and band gaps become narrower. This change in the electronic structure makes charge transfer between adsorbate and substrate levels and spin pairing with atomic H more facile.

The possible mismatch between the theoretical and experimental absorption edge peaks in semiconductors in a magnetic field background may arise due to the approximation scheme used to analytically calculate the absorption coefficient. As a possible remedy we suggest to consider nontrivial boundary conditions on x–y plane by in-equivalently quantizing the exciton in background magnetic field. This inequivalent quantization is based on von Neumann's method of self-adjoint extension, which is characterized by a parameter Σ. We obtain bound state solution and scattering state solution, which in general depend upon the self-adjoint extension parameter Σ. The parameter Σ can be used to fine tune the optical absorption coefficient K(Σ) to match with the experiment.

Binding energy for an exciton (X) bound in a parabolic two-dimensional quantum dot by an acceptor impurity A^- located on the z-axis at a distance d from the dot plane, are calculated using the Hartree formalism with a recently developed numerical method (PMM) for the solution of the Schrödinger equation. As our analysis indicates there is a critical dot radius R^c such that for R < R^c the complex (A^-, X) is unstable and with an increase of the impurity distance this critical radius increases. Furthermore, there is a critical value σ^c of the mass ratio such that for σ > σ^c the complex is stable.

The effect of the hopping term in the formation of excitons is studied in semiconductor nanostructures where electrons and holes are spatially separated by a potential barrier. We use the lattice gas model where electron–hole system is divided into unit cells with the effective lattice constant being of the order of the exciton size. The exciton density is calculated as a function of the disorder for several fixed values of the hopping integral. It is found that as the value of the hopping integral increases the exciton density decreases rapidly both for weak and strong disorder. Electronic correlation is treated explicitly by introducing repulsion between equally charged carriers and attraction between an electron and a hole from neighboring cells.

We study the role of many-body correlations in the ultrafast dynamics of quantum well magnetoexcitons. In linear response, inter-Landau level transitions are suppressed if magnetic field is stronger than magnetoexciton binding energy. However, in nonlinear response, two-electron Auger processes remain unsuppressed even at very strong field. We show that Auger scattering plays a dominant role in the coherent exciton dynamics in strong magnetic field. We perform numerical calculations of four-wave-mixing (FWM) polarization which incorporate Auger processes nonperturbatively, and find a strong amplitude enhancement of the FWM signal accompanied with polarization oscillations at negative time delays. We identify these oscillations as quantum beats between dark two-exciton states related to each other via Auger processes.

Photoluminescence as a function of temperature and magnetic field from single walled carbon nanotube solutions is described. This is modelled assuming that it is dominated by the small energy splitting between the dark and bright states of the singlet excitons which are found to be in the region of 1-5 meV for nanotubes of 0.8-1.2nm. The emission energies show a large red-shift due to the introduction of an Aharanov-Bohm phase by magnetic field along the tube axis and the luminescence intensity is strongly enhanced at low temperatures due to the mixing of the different valley states of the excitons.

The possibility of excitons bound to magnetic impurities in a two-dimensional system quantized by a strong magnetic field is considered. We show that the Landau quantization leads to dramatic changes in the structure of these bound excitons. Such changes are due primarily to a lower symmetry, which lifts the selection rules in the hybridization integrals, and in turn leads to a threshold van Hove singularity of the density of states in a two-dimensional system. Hence, a bound exciton with zero angular momentum, m = 0, is captured by a spin selective potential of the deep impurity levels.

Modifications of photoluminescence (PL) spectra taken from modulation doped CdTe/CdMgTe quantum well (QW) structures have been studied in magnetic fields up to 45T as a function of 2D electron concentration.

We examine a quantum dot (QD) illuminated in the near field with subwavelength spatial resolution, while simultaneously it is subjected to a magnetic field of variable orientation and magnitude. The magnetic field orientation can conserve or destroy the zero-magnetic-field ("structural") symmetry. The asymmetry induced by the magnetic field -except for specific orientations along symmetry axes- can be uncovered in the near-field (NF) but not in the far-field (FF) spectra. We predict that NF magnetoabsorption experiments of realistic spatial resolution could reveal the QD symmetry. This exceptional symmetry-resolving power of the near-field optics, is lost in the far field.

The tubular nature of single-walled carbon nanotube (SWCNT) crystals allows them to exhibit non-intuitive quantum phenomena when threaded by a magnetic flux, which breaks the time reversal symmetry and adds an Aharonov-Bohm phase to the circumferential boundary conditions on the electronic wave function. We demonstrate that such a symmetry-breaking magnetic field can dramatically "brighten" an optically-inactive, or dark, exciton state at low temperature. This phenomenon, magnetic brightening, can be understood as a consequence of interplay between the strong intervalley Coulomb mixing and field-induced lifting of valley degeneracy. Most recently, we made the direct observation of the dark excitonic state in individual SWCNTs using low-temperature micro-photoluminescence (PL) and and verified the importance of a parallel, tube-threading magentic field with ensemble spectroscopy. For micro-PL, a magnetic field up to 5 T, applied along the nanotube axis, brightened the dark state, leading to the emergence of a new emission peak. The peak rapidly grew in intensity with increasing field at the expense of the originally-dominant bright exciton peak and finally became dominant at fields > 3 T. The directly measured dark-bright splitting values were 1-4 meV for tube diameters 1.0-1.3 nm. For ensemble PL, we used fields up to 55 T in two collection geometries to demonstrate the importance of the tube-threading component. These experiments have provided one of the most critical tests for recently-proposed theories of 1-D excitons taking into account the strong 1-D Coulomb interactions and unique band structure on an equal footing.

We consider a restricted three-body problem, where two interacted particles are located in a two-dimensional (2D) plane and interact with the third one located in the parallel spatially separated plane. The system of such type can be formed in the semiconductor coupled quantum wells, where the electrons (holes) and direct excitons spatially separated in different parallel neighboring quantum wells are sufficiently close to interact and form negative X^- or positive X⁺ indirect trions. It is shown that at large interwell separations, when the interwell separation is much greater than the exciton Bohr radius, this problem can be solved analytically using the cluster approach. Analytical results for the energy spectrum and the wavefunctions of the spatially indirect trion are obtained, their dependencies on the interwell separations is analyzed and a conditional probability distribution is calculated. The formation of 2D Wigner crystal of trions at the low densities is predicted. It is shown that the critical density of the formation of the trion Wigner crystal is sufficiently greater than the critical density of the electron Wigner crystal in the same material.

An asymptotic procedure is proposed for solving the kinetic equations of carriers and phonons, together with photons and excitons. Both the direct and the exciton-catalized generation-recombination processes are accounted for. The generation rate shows a nonlinear behavior with respect to the product of the number densities of electrons and holes.

In this paper, we analyze two phase transitions in exciton bilayer systems: a topological phase transition to a phase which hosts Majorana fermions and a phase transition to a Wigner crystal. Using generic simple models for different phases, we discuss the conductance properties of the latter when contacted to metallic leads and demonstrate the possibility to observe the different phase transitions by simple conductance measurements.

We discuss the role of gravitational excitons/radions in different cosmological scenarios. Gravitational excitons are massive moduli fields which describe conformal excitations of the internal spaces and which, due to their Planck-scale suppressed coupling to matter fields, are WIMPs. It is demonstrated that, depending on the concrete scenario, observational cosmological data set strong restrictions on the allowed masses and initial oscillation amplitudes of these particles.

Magnetic field and intense laser radiation effects on the exciton binding energy and interband optical transitions in quantum well wires is calculated using a variational method and in the effective mass approximation. The results obtained show that the exciton binding energies and op interband absorption depend on the sizes of the quantum well wire, intense laser field and magnetic field. The additional confinement of the particles in the quantum well wire offers greater variety of the intense laser field and magnetic field dependence in comparison to three- and two-dimensional materials.

We review the concepts of excitons and excitonic polaritons, their nonlinear optical properties in nanostructures and their applications within integrated electronics and optoelectronics. Various theoretical aspects of excitons and excitonic polaritons are introduced, followed by a summary of their experimental and application-specific development in nanostructures at the electronic and photonic engineering levels. A number of technical applications are highlighted.

In this paper, we continue the theoretical study of changes in optical characteristics of superlattices as a consequence of some specific behavior of excitons. Based on the particular dispersion law and the spectral distribution of excitons, we have formulated and calculated the refractive indices of these structures and defined how refractive indices change with external electromagnetic field. It was determined that among wide variety of parameters governing calculus, only two parameters have a significant effect on exciton energy spectra and calculated optical quantities: (a) the number of film layers which constitute superlattice; (b) ratio of the exciton energy transfer between the layers of one film and on the boundary between two different films.

Time-resolved and time-integrated circularly-polarized photoluminescence of excitons and trions have been studied in external magnetic fields up to 10 T. ZnSe-based quantum well structures of n-type with carrier densities varied from 5×10⁹ to 10¹¹cm^-2 were used in this study. Absence of the chemical equilibrium in the exciton–trion system has been demonstrated at low temperatures (<10 K). The recovery of the equilibrium has been found at elevated temperatures (<15 K).

We report on a theoretical study of the fine structure of excited excitonic levels in semiconductor quantum disks. A particular attention is paid to the effect of electron–hole long-range exchange interaction. We demonstrate that even in the axisymmetric quantum disks, the exciton P-shell is split into three sublevels. The analytical results are obtained in the limiting cases of strong and weak confinement. A possibility of exciton spin relaxation due to the resonant LO-phonon-assisted coupling between the P and S shells is discussed.

Results of experimental studies of photoluminescence (PL) and PL excitation (PLE) spectra of MBE grown single quantum wells (QWs) formed by insertion of few CdSe monolayers in the ZnSe matrix are reviewed. PL spectra of such quantum objects originate from the luminescence of CdSe-rich nanoislands. Two types of island emitting states, namely ground and metastable ones, contribute to the low- and high-energy parts of the PL band, respectively. An interplay between these contributions is responsible for the anomalous temperature dependence of the maximum position of the PL band. The optical orientation and optical alignment experiments at resonant excitations allow to elucidate the nature of the two types of the emitting states. PLE spectra of ground and metastable states have strongly differing characters at excitation below some characteristic energy E_ME which is identified as the exciton percolation threshold. A theoretical model of the absorption spectra of emitting island states is presented, and practical applications of the model for the characterization of the island lateral concentration profiles are reported.