  We predict here the fine structure of an electrically tunable negatively
charged exciton (trion) composed of two electrons and a hole confined in a
gated bilayer graphene quantum dot (QD). We start with an atomistic approach,
allowing us to compute confined electron and confined hole QD states for a
structure containing over one million atoms. Using atomistic wavefunctions we
compute Coulomb matrix elements and self-energies. In the next step, by solving
the Bethe-Salpeter-like equation for trions, we describe a negatively charged
exciton, built as a strongly interacting interlayer complex of two electrons in
the conduction band and one hole in the valence band. Unlike in conventional
semiconducting QDs, we show that the trion contains a fine structure composed
of ten states arising from the valley and spin degrees of freedom. Finally, we
obtain absorption into and emission from the trion states. We predict the
existence of bright low-energy states and propose to extract the fine structure
of the trion using the temperature dependence of emission spectra.
