Morphological study of aluminum tris (8-hydroxyquinoline) thin films using infrared and Raman spectroscopy

We present comprehensive Raman spectra for thin films of Alq3, annealed at various temperatures up to 300 °C, over the range of 70–1800 cm−1. These spectra give strong evidence for structural rearrangement of thin films of Alq3 upon annealing at temperatures above 200 °C. Needle like crystals are observed to grow in the films and confirmed to be comprised of the α-Alq3 polymorph using the low energy Raman spectra. Furthermore, no evidence of the fac isomer or thermal interconversion between the mer and fac isomers of Alq3 was observed in either the infrared or Raman spectra of the thin films or powder. These results may have implications for the long-term efficiencies of organic light emitting diodes incorporating thin films of Alq3.