  Considerable similarity between positronium atom and an exciton in a quantum
dot is indicated. Following this, we apply the calculation regime from the
theory of excitons to describe some aspects of formation of a positronium in
matter. We consider the possibility of photonic deexcitation during Ps
formation and show the way of calculation of its probability. The photonic
transitions speculated here, if detected, allows improving experimental studies
of solid matter with positron techniques.
