Luminescence decay time and quantum yield of a pyrene single crystal are observed by a pulse method between 40-300 k. The temperature dependence on the intrinsic life time of emissions shows a peculiar character. The abrupt change of the analyzed intrinsic life time corresponds to the critical temperature of the phase transition. The mechanism of the phase transition is attributed to the formation of the trapped excimer excitons which deform the lattice around them. Further, the phase transition is concluded as the first kind type.