Fluorescence spectra of molecular guests at several temperatures are useful technique to study several types of polymer properties. In particular, it has been often employed to study polymer relaxation processes either in static or in dynamic conditions. In this work some applications of the steady-state fluorescence spectroscopy of different guests in polyethylene and in particular reports the photophysical behavior of 1,3-di(1-pyrenyl)propane (1Py(3)1Py) sorbed in low density polyethylene are shown. This molecular probe differs of pyrene by its ability to form intramolecular excimer species and we discuss the temperature dependence of this formation. In this study we recorded simultaneously the fluorescence spectra and the differential scanning calorimetry (dsc) traces. The relative dependence of fluorescence intensities on temperature of the higher energy vibronic band at 367 nm, of the isolated choromophore emission and of the excimer emission were discussed and associated with the polyethylene polymer relaxation processes. The influence of the macroscopic stretching upon the polymer relaxation processes and the fluorescence emission was also investigated and compared with previous results.