We discuss the temperature dependence of various photoluminescence transitions observed in undoped and doped GaN in the 9 to 300 K range. Samples grown using different techniques have been assessed. The mechanism underlying the various quenching behaviors observed is investigated using simple rate equations. In undoped GaN, the temperature dependence of the band edge excitonic lines is well described by assuming that the A exciton population is the leading term in the 50 to 300 K range. The activation energy for free exciton quenching is of the order of the Rydberg, suggesting that free hole release leads to non-radiative recombination. In slightly p-doped samples, the luminescence is dominated by acceptor-related transitions, whose intensity is also governed by release of free holes. For large p-type doping (p(300 K) greater than or equal to 10(17) cm(-3)), the activation energy for quenching is in the 60 to 90 meV range.