Energy transfer from a semiconductor quantum dot to an organic matrix

Forster energy transfer from an excited semiconductor quantum dot to the surrounding organic material is considered. While earlier only the calculations for the lowest excited state of the dot were performed and only the limiting cases of strong and weak confinement were analyzed, in this work we present the results for the crossover region, obtained from the variational calculation. We also consider the transfer from the higher excited states, which may be relevant if the carrier relaxation in the dot is inhibited due to the discreteness of the states. We employ a microscopic quantum mechanical description of the Wannier-Mott exciton in the quantum dot and a macroscopic description of the organic medium. According to our calculations, for II-VI type semiconductors (like CdSe) and strongly absorbing organics (like PTCDA) the energy transfer may occur on time scales of several tens of picoseconds, which is significantly less than the quantum dot excitation lifetime in the absence of such transfer. Thus, as in the case of quantum wells, the Forster mechanism may be an efficient tool for pumping organic light-emitting substances. In this paper we also consider how the carrier intraband relaxation time in the dot may be affected by the Forster energy transfer.