Temperature dependence of photoluminescence efficiency in doped and blended organic thin films

The temperature dependence of photoluminescence (PL) efficiency in fluorescent dye-doped tris(8-hydroxyquinoline)aluminum (Alq3) layers and blended Alq3 layers was investigated. Results show that the PL efficiency in the fluorescent dye-doped Alq3 layers has only weak temperature dependence, which is in contrast to the dramatic decrease of PL efficiency observed upon increasing temperature for undoped Alq3. This phenomenon is attributed to the narrower energy bandgap of the dopant, as compared to that of Alq3, which leads to the ‘trapping’ of mobile excitons on dopant molecules, hence impeding their migration by thermally activated diffusion, thereby decreasing their encounters with randomly distributed non-radiative recombination (i.e. quenching) sites.