Regensburg 2004 – scientific programme

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SYOH: Organic and Hybrid Systems for Future Electronics

SYOH 5: Poster

SYOH 5.89: Poster

Thursday, March 11, 2004, 18:00–21:00, B

EPR spectroscopy on different phases of electroluminescent Alq₃ — •A. Mirea^1,2, M. N. Grecu², M. Cölle¹, and M. Schwoerer¹ — ¹Experimentalphysik II, Universität Bayreuth, D-95440 Bayreuth — ²National Institute for Materials Physics, R-76900 Bucharest, Romania

Tris(8-hydroxyquinolino)aluminum (Alq₃) is one of the most extensive used electron conductor and emitting layer material in organic light-emitting devices (OLED’s). We report on X- and Q-band temperature dependence EPR experiments on different crystalline Alq₃ phases formed by using the train sublimation method. The room temperature X-band EPR spectra show two types of signals centered at g=2 and g=4 whose relative intensity are dependent on the crystalline phase nature. The g=2 signal is of a very particular nature - its intensity is temperature independent between 10-300 K for all phases, and increases of 4-6 times under room temperature e⁻- or γ -irradiation. By choosing appropriate annealing conditions (663-673 K temperature range, inert atmosphere) of as prepared Alq₃ phases, new features in the Q-band EPR spectra appear. Their simulation and analysis based on a spin Hamiltonian appropriate to a high spin system (S =1, S=3/2) is in good agreement with the existence of triplet and quartet spin states in annealed Alq₃. The D and E zero field parameters are evaluated. The EPR results, correlated with others investigation methods, are discussed in terms of different molecular models.