Effect of swift heavy ion irradiation on photoluminescence of Tris-(8-hydroxyquinoline)aluminum thin films

We report the effect of swift heavy ions (SHI) of 40 MeV Li3+ ions on Tris-(8-hydraxyquinoline) aluminum (Alq3) thin films deposited by thermal evaporation process on glass substrates. To understand the effect of the temperature-dependent optical properties, these thin films were irradiated both at 300 K and ~ 77 K and were characterized by photoluminescence (PL), Infrared (IR) and time resolved photoluminescence (TRPL) spectroscopy. The PL and lifetime of SHI irradiated both at 300 K and ~ 77 K Alq3 thin films were found to decrease with ion fluences compared to as-deposited Alq3 thin films. This is due to the quenching of excitons by the defects created by SHI irradiation. The significant decrease in PL and lifetime of SHI irradiated (~ 77 K) Alq3 thin films is attributed to the increased defect density, caused by the frozen charge carriers and poor molecular overlap resulting in weak bonding between Alq3 molecules at low temperature.