The photoluminescence (PL) of heavily Te-doped GaSb has been investigated for different free carrier concentrations. A careful line shape analysis of the dominant free-to-bound transition has been performed using nonparabolic bands and taking into account the band tailing through the Kane model. The Fermi level and the band edge position have been determined from the fit of the PL band. Our results show that the energy gap value is significantly lower than in lightly doped and undoped material. This band-gap narrowing can be well understood taking into account both manybody interaction (exchange) and the random impurity distribution, that induces a rigid shift of the bands toward each other and tail states into the forbidden gap, respectively. Measurements have been performed at different temperatures and excitation power densities to evidence the role of the acceptor fluctuation and of the minority carrier distribution in determining the optical emission energy. Simple relations connecting the band-gap narrowing and the PL linewidth to the free carrier concentration are proposed in GaSb. ©1997 American Institute of Physics.