Excitation spectrum, relaxation and coherence of single self-assembled CdSe quantum dots

We report on ultra-narrow, long-term stable emission of single, self-assemb led CdSe/ZnSe QDs. The excitation spectrum reveals a spectrally sharp excit ed state with a lifetime of 1.5 ps, related to the LO-phonon decay. In addi tion, excitation features due to optical and acoustic phonons are present. A strong increase of the exciton-acoustic-phonon coupling is found. The spi n relaxation time is much longer than the exciton lifetime of 250 ps. Under resonant excitation, photon brats from a single QD are seen. Coherence of the purely radiatively damped QD exciton is maintained until it recombines.