Optical absorption in AlQ

In this paper, we report on optical absorption in thin films of tris(8-hydr oxyquinoline)aluminium (A1Q) between 0.7 and 5 eV. We report on the first m easurement of the sub-bandgap absorption in A1Q using Photothermal Deflecti on Spectroscopy (PDS) for different deposition conditions. The sub-bandgap absorption is not very sensitive to sample deposition temperature but incre ases on exposure to atmosphere. We present a simple model to explain the ab sorption data. We calculate the density of states in the gap to be about 6. 10(17)/cm(3) and present evidence that the fermi level lies in the upper ha lf of the band gap close to the LUMO level in A1Q. (C) 2000 Elsevier Scienc e S.A. All rights reserved.