Charge carrier traps in tris-(8-hydroxyquinoline) aluminum

Thermoluminescent measurements between 40 and 300 C revealed two traps in the irradiated Alq3 powder synthetized from Al(OH)3, at 0.8 and 1.1 eV below the conduction band. These two traps have been assigned with the Alq3 facial and meridional isomers and the trapping process stand for a long time after the switching off the irradiation source. The spectra recorded an hour after switching recover 60% from the photoluminescence and also decreasing the TL signals. A theoretical model was proposed in order to explain the trapping and de-trapping processes in both meridional and facial Alq3 isomers based on the XPS measurements for the HOMO, LUMO, ionization potential and optical bandgap, completed with the DFT calculated parameters and similar experimental results concerning the evidences of the triplet states in Alq3 compound.