A. S. Moskalenko

Single-particle states in spherical Si/SiO2 quantum dots

in a multiband effective mass approximation. Luttinger Hamiltonian is used for holes and thestrong anisotropy of the conduction electron effective mass in Si is taken into account. As boundaryconditions for electron and hole wave functions we use continuity of the wave functions and thevelocity density at the boundary of the quantum dots.

Direct bandgap optical transitions in Si nanocrystals

The effect of quantum confinement on the direct bandgap of spherical Si nanocrystals has been modelled theoretically. We conclude that the energy of the direct bandgap at the Γ-point decreases with size reduction: quantum confinement enhances radiative recombination across the direct bandgap and introduces its “red“ shift for smaller grains. We postulate to identify the frequently reported efficient blue emission (F-band) from Si nanocrystals with this zero-phonon recombination. In a dedicated experiment, we confirm the “red“ shift of the F-band, supporting the proposed identification.

Energy transfer in Er-doped SiO2 sensitized with Si nanocrystals

We present a high-resolution photoluminescence study of Er-doped SiO2 sensitized with Si nanocrystals (Si NCs). Emission bands originating from recombination of excitons confined in Si NCs and of internal transitions within the 4f-electron core of Er3+ ions, and a band centered at lambda = 1200nm have been identified. Their kinetics have been investigated in detail. Based on these measurements, we present a comprehensive model for energy transfer mechanisms responsible for light generation in this system. A unique picture of energy flow between subsystems of Er3+ and Si NCs is developed, yielding truly microscopic information on the sensitization effect and its limitations. In particular, we show that most of the Er3+ ions available in the system are participating in the energy exchange. The long standing problem of apparent loss of optical activity of majority of Er dopants upon sensitization with Si NCs is clarified and assigned to appearance of a very efficient energy exchange mechanism between Si NCs and Er3+ ions. Application potential of SiO2:Er sensitized by Si NCs is discussed in view of the newly acquired microscopic insight.

Light-induced valley currents and magnetization in graphene rings

We study the non-equilibrium dynamics in a mesoscopic graphene ring excited by picoseconds shaped electromagnetic pulses. We predict an ultrafast buildup of charge polarization, currents and orbital magnetization. Applying the light pulses identified here, non-equilibrium valley currents are generated in a graphene ring threaded by a stationary magnetic flux. We predict a finite graphene ring magnetization even for a vanishing charge current; the magnetization emerges due to the light-induced difference of the valley populations.

Excitation of Er3+ ions in SiO2 with Si nanocrystals

Probabilities of excitation of erbium ions via Coulomb interaction with carriers localized in silicon nanocrystals embedded in SiO2, in recombination and intraband relaxation of these carriers, have been calculated.

Carrier relaxation in Si/SiO2 quantum dots

Carrier relaxation due to both optical and nonradiative intraband transitions in silicon quantum dots (QDs) in SiO2SiO2 matrix is considered. Interaction of confined holes with optical phonons is studied. The Huang–Rhys factor governing intraband transitions induced by this interaction is calculated. The probability of intraband transition of a confined hole emitting several optical phonons is estimated.

Carrier relaxation in Si/SiO2Si/SiO2 quantum dots

Carrier relaxation due to both optical and nonradiative intraband transitions in silicon quantum dots (QDs) in SiO2SiO2 matrix is considered. Interaction of confined holes with optical phonons is studied. The Huang–Rhys factor governing intraband transitions induced by this interaction is calculated. The probability of intraband transition of a confined hole emitting several optical phonons is estimated.

Carrier relaxation in quantum dots

Carrier relaxation due to both optical and nonradiative intraband transitions in silicon quantum dots (QDs) in SiO2SiO2 matrix is considered. Interaction of confined holes with optical phonons is studied. The Huang–Rhys factor governing intraband transitions induced by this interaction is calculated. The probability of intraband transition of a confined hole emitting several optical phonons is estimated.

Energy transfer in Er-dopedSiO2sensitized with Si nanocrystals

We present a high-resolution photoluminescence study of Er-doped SiO2 sensitized with Si nanocrystals (Si NCs). Emission bands originating from recombination of excitons confined in Si NCs and of internal transitions within the 4f-electron core of Er3+ ions, and a band centered at lambda = 1200nm have been identified. Their kinetics have been investigated in detail. Based on these measurements, we present a comprehensive model for energy transfer mechanisms responsible for light generation in this system. A unique picture of energy flow between subsystems of Er3+ and Si NCs is developed, yielding truly microscopic information on the sensitization effect and its limitations. In particular, we show that most of the Er3+ ions available in the system are participating in the energy exchange. The long standing problem of apparent loss of optical activity of majority of Er dopants upon sensitization with Si NCs is clarified and assigned to appearance of a very efficient energy exchange mechanism between Si NCs and Er3+ ions. Application potential of SiO2:Er sensitized by Si NCs is discussed in view of the newly acquired microscopic insight.