  Spatially indirect excitons in semiconducting double quantum wells have been
shown to exhibit rich collective many-body behavior that result from the nature
of the extended dipole-dipole interactions between particles. For many
spectroscopic studies of the emission from a system of such indirect excitons,
it is crucial to separate the single particle properties of the excitons from
the many-body effects arising from their mutual interactions. In particular,
knowledge of the relation between the emission energy of indirect excitons and
their radiative lifetime could be highly beneficial for control, manipulation,
and analysis of such systems. Here we study a simple analytic approximate
relation between the radiative lifetime of indirect excitons and their emission
energy. We show, both numerically and experimentally, the validity and the
limits of this approximate relation. This relation between the emission energy
and the lifetime of indirect excitons can be used to tune and determine their
lifetime and their resulting dynamics without the need of directly measuring
it, and as a tool for design of indirect exciton based devices.
