Optical absorption in Alq

In this paper, we report on the optical absorption of tris(8-hydroxyquinolato) aluminium (Alq) sublimed thin films between 0.7 and 5 eV and compare it with absorption in solution between 1.5 and 5 eV. Specifically, we show that above 2.5 eV the absorption in solution and in the thin film are very similar to each other. The absorption falls off exponentially with energy from 3.18 eV in both thin film and in solution. Below 2.5 eV the absorption spectrum of the thin film changes qualitatively and is nearly independent of energy down to 0.7 eV. Exposure of the film to atmosphere significantly affects the subband gap absorption and causes an increase in the defect density. (C) 2001 Elsevier Science B.V. All rights reserved.