Light-induced orientation of electron spins in the negatively charged InP quantum dots is found to persist longer than 100 s. We have proved experimentally that the long-lived orientation is due to slow relaxation of the electron spins rather than to the dynamic nuclear polarization effects.

Photoluminescence (PL) and reflectivity spectra of a high-quality InGaAs/GaAs quantum well structure reveal a series of ultra-narrow peaks attributed to the quantum confined exciton states. The intensity of these peaks decreases as a function of temperature, while the linewidths demonstrate a complex and peculiar behavior. At low pumping the widths of all peaks remain quite narrow (< 0.1 meV) in the whole temperature range studied, 4 -30 K. At the stronger pumping, the linewidth first increases and than drops down with the temperature rise. Pump-probe experiments show two characteristic time scales in the exciton decay, < 10 ps and 15 -45 ns, respectively. We interpret all these data by an interplay between the exciton recombination within the light cone, the exciton relaxation from a nonradiative reservoir to the light cone, and the thermal dissociation of the nonradiative excitons. The broadening of the low energy exciton lines is governed by the radiative recombination and scattering with reservoir excitons while for the higher energy states the linewidths are also dependent on the acoustic phonon relaxation processes.

The paper reports on quantum beats observed in the photoluminescence kinetics of a single layer of the InP self-assembled quantum dots in a magnetic field. It is found that the beats arise only after removal of excess charges from the quantum dots by an external electrical bias. The quantum beats are shown to be related to the interference of the excitonic fine-structure states split by the magnetic-field. The dependences of the beat characteristics on the magnetic-field strength and orientation are studied. Theoretical analysis based on a model spin Hamiltonian has allowed us to describe adequately the shape of the oscillating component of the signal. We have determined the values of the electron g-factor components and estimated the spread and the mean value of the hole g factor, as well as of the electron-hole exchange splitting parameters.

The nuclear spin dynamics in an ensemble of singly charged ͑In,Ga͒As/GaAs quantum dots has been studied at a temperature of 1.6 K. The effective magnetic field of nuclear polarization was detected through the circular polarization of quantum dot photoluminescence. The polarization is reduced if an external magnetic field compensates the nuclear field. To study the time evolution of the nuclear field, a photoluminescence pumpprobe technique has been developed, from which we find a complex behavior of the nuclear-polarization dynamics; its rise is considerably slowed down when the effective field of polarized nuclei exceeds that of the nuclear spin fluctuations. A phenomenological model for the dynamics of a strongly coupled electron-nuclear spin system has been developed, whose results qualitatively agree with the experimental data.