  The photoluminescence spectra of band-edge transitions in GaN is studied as a
function of temperature. The parameters that describe the temperature
dependence red-shift of the band-edge transition energy and the broadening of
emission line are evaluated using different models. We find that the
semi-empirical relation based on phonon-dispersion related spectral function
leads to excellent fit to the experimental data. The exciton-phonon coupling
constants are determined from the analysis of linewidth broadening.
