  Three-particle complexes consisting of two holes in the completely filled
zero electron Landau level and an excited electron in the unoccupied first
Landau level are investigated in a quantum Hall insulator. The distinctive
features of these three-particle complexes are an electron-hole mass symmetry
and the small energy gap of the quantum Hall insulator itself. Theoretical
calculations of the trion energy spectrum in a quantizing magnetic field
predict that, besides the ground state, trions feature a hierarchy of excited
bound states. In agreement with the theoretical simulations, we observe new
photoluminescence lines related to the excited trion states. A relatively small
energy gap allows the binding of three-particle complexes with magnetoplasma
oscillations and formation of plasmarons. The plasmaron properties are
investigated experimentally.
