Photoinduced energy transfer in poly(trimethylene terephthalate) (PTT) was investigated by examining its excitation wavelength and concentration dependences of fluorescence in solutions. Accordingly, critical quench concentration and critical trap formation concentration were identified. Besides, studies of temperature effect on photoluminescence (PL) behavior of amorphous PTT film from -183 to + 177 degrees C revealed that both fluorescence and phosphorescence emissions at low temperature can be attributed to monomers and traps. Phosphorescence quenching originated from the discontinuous increase of nonradiative processes. The corresponding quenching activation energies were estimated to be 13.5 kJ/mol for monomer phosphorescence quenching and 17.2 kJ/mol for exciplex phosphorescence quenching, respectively. Furthermore, the PL method proved to be able to monitor molecular relaxations (including gamma-, beta-, and alpha-transitions) and cold crystallization in PTT film, which used to be measured by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC), respectively.