Bright and dark exciton transfer in quantum dot arrays

We theoretically study nonradiative and radiative resonance energy transfer between two localized quantum emitters, a donor (initially excited quantum dot) and an acceptor (quantum dot receiving the excitation). We find that the donor lifetime can be significantly modified only due to the nonradiative dipole-dipole Förster Resonance energy transfer process to the short living energy level in acceptor dot at donor - acceptor separations of approximately 5-15 nm (depending on the acceptor radiative lifetime) and for the energy detuning not larger than ~1-2 meV. The dark (spin forbidden) exciton states can participate in the Forster energy transfer due to the weak admixture of the bright exciton states to the dark states, which also allows the radiative recombination of the dark excitons. We demonstrate the dominant role of the dark exciton in the low temperature energy transfer in ensemble of closely packed CdTe nanocrystals by time-dependent photoluminescence spectroscopy in applied external magnetic field which considerably enhances this admixture. The Förster Resonance energy transfer in inhomogeneous dense arrays of epitaxial CdSe/ZnSe quantum dots is also demonstrated by time-and space-resolved photoluminescence spectroscopy. The work was supported by Russian Science Foundation (Project number 14-22-00107)