  We demonstrate that the temperature and doping dependencies of the
photoluminescence (PL) spectra of a doped MoS2 monolayer have several peculiar
characteristics defined by trion radiative decay. While only zero-momentum
exciton states are coupled to light, radiative recombination of non-zero
momentum trions is also allowed. This leads to an asymmetric broadening of the
trion spectral peak and redshift of the emitted light with increasing
temperature. The lowest energy trion state is dark, which is manifested by the
sharply non-monotonic temperature dependence of the PL intensity. Our
calculations combine the Dirac model for the single-particle states, the
parameters for which are obtained from the first principle calculations, and
the direct solution of the three-particle problem within the Tamm-Dancoff
approximation. The numerical results are well captured by a simple model that
yields analytical expressions for the temperature dependencies of the PL
spectra.
