Thermoluminescence experiments were performed on charged and uncharged polyethylene terephthalate films. Four peaks have been identified at -140, 0, 110 and 160 °C. With the help of different techniques, it was possible to identify possible molecular processes responsible of the radiative recombination of trapped charge carriers. The peak at -140 °C has been associated with the β1 relaxation (carboxyl groups). The peak at 0°C can be related to charge carriers stored in traps at 0.36 eV, which are possibly stimulated by the β2 relaxation. The third peak (110 °C) is to the α relaxation. At 160 °C, it is possible to observe the fourth TL-glow peak, which could be related to the movement of the crystallites as a whole entity.