Thermoluminescence and electroluminescence of annealed polyfluorene layers Dessislava Sainova a,b , Dieter Neher b, * , Ewa Dobruchowska c , Beata Luszczynska c , Ireneusz Glowacki c , Jacek Ulanski c , Heinz-Georg Nothofer d , Ulli Scherf e a Fraunhofer Institute for Applied Polymer Research, Geiselbergstrasse 69, D-14476 Golm, Germany b Institute of Physics, University of Potsdam, Am Neuen Palais 10, D-14469 Potsdam, Germany c Department of Molecular Physics, Technical University of Lodz, Zeromskiego 116, 90-924 Lodz, Poland d SONY International (Europe) GmbH, Materials Science Laboratories, Advanced Technology Center Stuttgart, Heinrich-Hertz-Str. 1, 70327 Stuttgart, Germany e Department of Chemistry, University of Wuppertal, Gaußstr. 20, 42097 Wuppertal, Germany Received 17 September 2002; in final form 21 January 2003 Abstract As-prepared and annealed layers of polyfluorene were studied by thermoluminescence (TL), photoluminescence (PL) and electroluminescence (EL). Upon annealing at the transition to the liquid-crystalline phase, the green emission in PL and EL becomes more pronounced. At the same time the TL spectrum broadens towards higher temperatures, indi- cating the introduction of additional trapping sites. In contrast, photooxidation does not broaden the TL spectrum, even so it significantly affects the emission spectra. We conclude that annealing causes the formation of non-/weakly emitting aggregates which compete with the undisturbed chains with respect to charge carrier capture and exciton recombination. Ó 2003 Elsevier Science B.V. All rights reserved. 1. Introduction Polyfluorene (PF) homopolymers are an im- portant class of emitting materials exhibiting bright blue emission of high efficiency [1–4] com- bined with thermotropic liquid crystallinity. The latter property allows for the orientation of PF onto suitable alignment layers [5–8]. Therefore, PFs are particularly attractive candidates for ap- plications in state-of-the-art light-emitting diodes (LEDs) and displays. However, the polyfluorene emission in the solid state often exhibits an undesirable green contri- bution. It is now well established that this partic- ular band origins from the radiative decay of excitons on PF segment carrying a fluorenone unit (keto-defect) [9]. Fluorenone formation has been shown to occur via the oxidation of fluorene dur- Chemical Physics Letters 371 (2003) 15–22 www.elsevier.com/locate/cplett * Corresponding author. Fax: +49-331-977-1290. E-mail address: neher@rz.uni-potsdam.de (D. Neher). 0009-2614/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0009-2614(03)00180-5