Interaction Range for Photoexcitations in Luminescent Conjugated Polymers

Low threshold solid-state lasers and high-efficiency LEDs (light-emitting diodes) based on semiconducting polymers would represent a major achievement. However, this entails identifying the nature of the excitations responsible for spontaneous and stimulated emission, a subject of continued controversy. Towards this end the time evolution of the emissive species in thin films of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene), MEH-PPV, was studied. A fast decay is observed at high excitation densities but disappears when the polymer is pumped at low fluence.