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

We present comprehensive Raman spectra for thin films of Alq(3), annealed at various temperatures up to 300 degreesC, over the range of 70-1800 cm(-1). These spectra give strong evidence for structural rearrangement of thin films of Alq(3) upon annealing at temperatures above 200 degreesC. Needle like crystals are observed to grow in the films and confirmed to be comprised of the alpha-Alq(3) polymorph using the low energy Raman spectra. Furthermore, no evidence of the fac isomer or thermal interconversion between the mer and fac isomers of Alq(3) 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 Alq(3). (C) 2002 American Institute of Physics.