  We report an optical characterization of ZnPSe$_3$ crystals that demonstrates
indirect band gap characteristics in combination with unusually strong
photoluminescence. We found evidence of interband recombination from excitonic
states with microsecond lifetimes. Through optical characterization, we
reconstructed the electronic band scheme relevant for fundamental processes of
light absorption, carrier relaxation and radiative recombination. The
investigation of the radiative processes in the presence of magnetic field
revealed spin polarization of fundamental electronic states. This observation
opens a pathway towards controlling the spin of excitonic states in
technologically relevant microsecond timescales.
