  We study the exponential functional $\int_0^\infty e^{-\xi_{s-}} \, d\eta_s$
of two one-dimensional independent L\'evy processes $\xi$ and $\eta$, where
$\eta$ is a subordinator. In particular, we derive an integro-differential
equation for the density of the exponential functional whenever it exists.
Further, we consider the mapping $\Phi_\xi$ for a fixed L\'evy process $\xi$,
which maps the law of $\eta_1$ to the law of the corresponding exponential
functional $\int_0^\infty e^{-\xi_{s-}} \, d\eta_s$, and study the behaviour of
the range of $\Phi_\xi$ for varying characteristics of $\xi$. Moreover, we
derive conditions for selfdecomposable distributions and generalized Gamma
convolutions to be in the range. On the way we also obtain new
characterizations of these classes of distributions.
