Optical absorption in Alq

In this paper, we report on the optical absorption of tris(8-hydroxyquinola to) 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 th at above 2.5 eV the absorption in solution and in the thin film are very si milar to each other. The absorption falls off exponentially with energy fro m 3.18 eV in both thin film and in solution. Below 2.5 eV the absorption sp ectrum of the thin film changes qualitatively and is nearly independent of energy down to 0.7 eV. Exposure of the film to atmosphere significantly aff ects the subband gap absorption and causes an increase in the defect densit y. (C) 2001 Elsevier Science B.V. All rights reserved.