Exciton-phonon coupling efficiency in CdSe quantum dots embedded in ZnSe nanowires

Abstract

Exciton luminescence of a CdSe quantum dot (QD) inserted in a ZnSe nanowire\nis strongly influenced by the dark exciton states. Because of the small size of\nthese QDs (2-5nm), exchange interaction between hole and electron is highly\nenhanced and we measured large energy splitting between bright and dark exciton\nstates ($\\Delta E\\in [4, 9.2 ]$ meV) and large spin flip rates between these\nstates. Statistics on many QDs showed that this splitting depends on the QD\nsize. Moreover, we measured an increase of the spin flip rate to the dark\nstates with increasing energy splitting. We explain this observation with a\nmodel taking into account the fact that the exciton-phonon interaction depends\non the bright to dark exciton energy splitting as well as on the size and shape\nof the exciton wave function. It also has consequences on the exciton line\nintensity at high temperature.\n