Characterizing coherence lengths of organic light-emitting devices using Newton's rings apparatus

We investigated the temporal coherence properties of organic light-emitting devices (OLEDs) by characterizing their coherence lengths. The interferometry based on the Newton's rings apparatus was adopted to characterize the coherence lengths of various OLEDs, including non-doped/doped OLEDs and non-cavity bottom-emitting/cavity top-emitting OLEDs. The types of OLEDs investigated exhibit coherence lengths of 3-10 mu m, depending on the device structures/emitters and spectral bandwidths of the OLED emission. OLEDs using emitting molecules with more limited number of allowed vibronic transitions give narrower-band and more coherent emission. Introducing the microcavity into the device structure to induce resonance also narrows the emission spectra and meanwhile increases the coherence length. Such information may be useful for modeling, design, and optimization of optical properties of OLEDs. (C) 2009 Elsevier B.V. All rights reserved.