OBSERVATION OF THE DARK EXCITON IN CDSE QUANTUM DOTS

We use external magnetic fields to identify the band edge emitting sta te in CdSe quantum dots. The field dependence of emission decays and L O phonon spectra show the importance of exciton spin dynamics in the r ecombination mechanism. To interpret our results we calculate the band edge exciton structure, including the effects of the electron-hole ex change interaction and a nonspherical shape. The exchange term, neglig ible in the bulk, is strongly enhanced by quantum confinement and allo ws the observation of an optically passive ''dark'' excitonic state.