  Photoluminescence of a single CdSe quantum dot embedded in a ZnSe nanowire
has been investigated. It has been found that the dark exciton has a strong
influence on the optical properties. The most visible influence is the strongly
reduced excitonic emission compared to the biexcitonic one. Temperature
dependent lifetime measurements have allowed us to measure a large splitting of
$\Delta E = 6 $ meV between the dark and the bright exciton as well as the spin
flip rates between these two states.
