EFFECT OF LOW-TEMPERATURE ANNEALING ON STRUCTURE AND OPTICAL PROPERTIES OF AMORPHOUS TRIS(8-HYDROXYQUINOLINE) ALUMINUM FILMS

Needle-shaped nanostructured tris(8-hydroxyquinoline) aluminum nanowires (Alq(3)) have been obtained by annealing Alq(3) amorphous films at 150 degrees C which is lower than the glass transition temperature of Alq(3) (172 degrees C). The growth of Alq(3) nanowires is attributed to the migration and stacking of Alq(3) molecules which acquire thermal energy from the annealing process. X-ray diffraction analysis and scanning electronic microscopy spectra show that the Alq(3) nanowires are composed of the well-known alpha-phase Alq(3). The intensity of the photoluminescence spectra firstly increases and then decreases as the annealing time increases, along with a spectral blue shift. The optical transmittance spectra of the annealed Alq(3) films show a smaller average absorption in the visible range and a wider optical bandgap compared with that of the amorphous films, as a result of the decrease of pi overlapping in the Alq(3) molecules.