Observation of phosphorescence from tris(8-hydroxyquinoline) aluminum thin films using triplet energy transfer from iridium complexes

Strong phosphorescence from tris(8-hydroxyquinoline) aluminum (Alq(3)) was observed in amorphous Alq(3) thin films doped with phosphorescent molecules, fac tris(2-phenylpyridine) iridium [Ir(ppy)(3)]. The energy-transfer and light-emission mechanisms were studied in the Ir(ppy)(3)-doped Alq(3) thin films. The triplet energy of Alq(3) was determined to be 2.03 eV from the highest-energy peak of the phosphorescence spectra, and the phosphorescence lifetime was 5.3 ms at 8 K. The phosphorescence lifetime and intensity significantly decreased With an increase in temperature, especially at temperatures above 100 K. From this study, we have found that the triplet energy transfer from Ir(ppy)(3) enables us to characterize the phosphorescence properties of Alq(3), and that Ir(PPY)(3) plays the important role of a phosphorescent sensitizer for Alq(3).