We have measured the photoluminescence (PL) decay time of free exciton (FE) and bound excitons (BE) related to nitrogen in epitaxial 4H-SiC layers with different doping concentration. It is shown that the recombination mechanism for FE is not connected with capture of e-h pair to defects related to nitrogen. The PL decay times for the Q BE, as well as for excitons bound to Ga, Al or B, are determined by the FE recombination time with the PL decay time values about 8 - 15 ns at low temperature. That is different for P BE, for which the time decay is about 40 ns at T = 2 K. In addition, detailed temperature studies of the PL decay were performed.