Luminescence properties of type-II quantum well light-emitting diodes formed with NPB and Alq3

The organic quantum well devices which are similar to the type-II quantum well of inorganic semiconductor have been fabricated. In the electroluminescence, the blue shift of spectrum with increasing applied voltage is observed, which is interpreted by exciton confinement effect and polarization effect, and the generation of exciton, including carrier injection and energy transfer, is discussed. This energy transfer from barrier to well is studied by photoluminescence and is interpreted in terms of Fo¨rster energy transfer. The electromodulation of photoluminescence demonstrates the quenching mainly comes from the dissociation of exciton in NPB and that in Alq3 is very stable.