Fluorescence lifetime of tris-(8-hydroquinoline) aluminum thin film and solution

The emission lifetime of tris-(8-hydroxyquinoline) aluminium (AlQ(3)) as a powder or a thin film from vaporization is measured at excitation wavelengt h similar to 400 nm. According to decay curves recorded with time-correlate d single photon counting, the lifetimes are 17 and 12 ns for powder and fil m, respectively. Because films formed by sublimation contain microcrystals (C. W. Tang, S. A. Van Slyke and C. H. Chen, J. Appl. Phys. 65, 3610 (1989) ), the measured lifetime reflects the structure and quality of the film. De cay curves of electronically excited AlQ(3) dissolved in methanol, ethanol, acetonitrile, trichloromethane and benzene are measured; the lifetimes are 9.3, 11, 9.9, 18 and 20 ns, respectively. The lifetime of excited AlQ(3) d ecreases with increasing solvent polarity; this trend is attributed to a di pole-dipole interaction associated with relaxation of AlQ(3). The quantum y ield of fluorescence of AlQ(3) in ethanol is measured to be 9.4 %.