Phase transition induced spectral tuning of dual luminescent crystalline zinc-phthalocyanine thin films and OLEDs

We analyze the impact of the first order structural phase transition between the α- and β-phases in crystalline zinc-phthalocyanine thin films on their luminescent behavior. Upon optical excitation, two intensity maxima governing the dual fluorescence can be attributed to thin film excimer emission of the α-phase at 930 nm and bulk Frenkel exciton emission of the corresponding β-phase at 780 nm. Comprehensive temperature and time dependent studies on the structural phase transition reveal a controllable shift of spectral weight between these two maxima. Applying this approach to thin film devices, we demonstrate the preparation of dual luminescent organic light emitting diodes with tunable emission characteristics in the near infrared, which are of interest as electro-optical units in future hybrid photonic devices.