We have used density-functional theory and the nudged elastic-band method to calculate migration pathways and estimated the activation energy for the diffusion of oxygen vacancies in a-quartz. While the energy barrier for the diffusion of a neutral vacancy is very high, 4.1 eV, the binding of a triplet-state exciton to the vacancy lowers the barrier to 1.7 eV and the attachment of a hole lowers...

Nanoscale systems are forecast to be a means of integrating desirable attributes of molecular and bulk regimes into easily processed materials. Notable examples include plastic light-emitting devices and organic solar cells, the operation of which hinge on the formation of electronic excited states, excitons, in complex nanostructured materials. The spectroscopy of nanoscale materials reveals d...

Organic solar cells have the potential to become a low-cost sustainable energy source. Understanding the photoconversion mechanism is key to the design of efficient organic solar cells. In this review, we discuss the processes involved in the photo-electron conversion mechanism, which may be subdivided into exciton harvesting, exciton transport, exciton dissociation, charge transport and extrac...

Exciton localization in ZnO /MgxZn1−xO quantum wells QWs has been investigated systematically with various ZnO well widths for the fixed Mg0.23Zn0.77O barrier height. A strong exciton confinement is observed with an implicit dependence on the built-in electric field which is calculated to be 0.37 MV/cm. The exciton-phonon coupling strength varied significantly depending upon the degrees of exci...

We analyze the excitons states in a quantum wire under intense laser radiation. Electrons and holes are confined by the parabolic potential of the quantum wire. An exactly solvable model is introduced for calculating the exciton binding energy, replacing the actual Coulomb interaction between the electron and the hole by a projective operator.

The binding energies o f l i gh t and heavyhole exciton-phonon systems i n GaAs-Ga A1 As quantum wires are calculated as a function o f the s i z e s o f the I-x x wire for Several values of the heights o f the barrier potential. I t is found that the corrections due t o exciton-phonon coupling are quite s igni f icant . In the last few years some progress has been done in the study of electron...

Recent surface techniques to fabricate and arrange quantum wires on the semiconductor surface have enabled to synthesize the artificial two-dimensional lattice systems such as square and triangle lattices. For example, C. Albrecht et al. produced a square lattice by arranging InAs wires on GaInAs (001) surface and showed that a butterfly energy spectra is seen in the case of applying the magnet...

Surface plasmon (SP) coupling has been successfully applied to nonradiative energy transfer via exciton-plasmon-exciton coupling in conventionally sandwiched donor-metal film-acceptor configurations. However, these structures lack the desired efficiency and suffer poor photoemission due to the high energy loss. Here, we show that the cascaded exciton-plasmon-plasmon-exciton coupling in stratifi...

We develop an orbital-dependent potential to describe electron-hole interaction in materials with structural 2D character, i.e. quasi-2D materials. The modulated orbital-dependent potentials are also constructed with non-local screening, multi-layer screening, and finite gap due to the coupling with substrates. We apply the excitonic Hamiltonian in coordinate-space with developed effective elec...

Charge transfer (CT) states and excitons are important in energy conversion processes that occur in organic light emitting devices (OLEDS) and organic solar cells. An ab initio density functional theory (DFT) method for obtaining CT-exciton electronic couplings between CT states and excitons is presented. This method is applied to two organic heterodimers to obtain their CT-exciton coupling and...