PHOTOOXIDATION EFFECTS ON PICOSECOND PHOTOLUMINESCENCE AND PHOTOCONDUCTIVITY IN TRIS-(8-HYDROXYQUINOLINE) ALUMINUM (ALQ3)

The photogeneration of radiative excited states and charge carriers in pristine and photooxidized tris-(8-hydroxyquinoline) aluminum (Alq(3) ) was studied by measuring both its photoluminescence and photoconduct ive response simultaneously, with subnanosecond resolution. 25 psec la ser pulses at 355nm were used for excitation of vacuum evaporated 2-4 mu m thick films of Alq(3). We observed that photooxidation of Alq(3) with oxygen and UV Light substantially decreases the fluorescence life time and quantum yield as well as the photoconductive response. This d ecrease is shown to be a result of quenching of singlet molecular exci tations by products of photooxidation of Alq(3).