Synchronized surface plasmon generation and scattering in organic light emitting diodes: measurements removing optical interference effect

It has been believed that the energy transfer of one exciton arising in an organic layer creates one SPP on a proximally-positioned metal surface. However, because excitons in the organic layer are close to one another, there is the possibility that multiple SPPs are generated in phase, entering an appearance of constructive interference among the scattered electromagnetic waves. This should lead to an increase in SPP scattering probability effectively. To investigate the possibility and light enhancement associated with this, we prepared a device consisting of Alq₃ on a quarter-wavelength dielectric multilayer film/glass as a reference instead of the usual Alq₃/glass substrate. This reference device eliminated the influence of complicated optical interference, and made it possible to calculate SPP-mediated light enhancement accurately. The contributions of SPPs and non-radiative components to light emission were adjusted in the calculation as the results corresponded with the measured enhancement dependence on Alq₃ thickness. As a result, it was found that the SPP scattering rate was larger than the ordinary calculation based on the assumption that excitons create SPPs randomly. In-phase energy transfer from excitons to SPPs is supported by evidences obtained from this study. (paper)