Structural aspects of electroluminescence in fullerene crystals

The emission of broadband electroluminescence from fullerene crystals is described. The intensity is nonlinearly dependent on the current. Observation of electroluminescence requires crystals of comparatively high conductivity and it is noted that the conductivities of crystals from the same batch can vary by orders of magnitude. When driven by high currents, the crystals undergo an irreversible increase in their conductance. In the region of the irreversibility, the electroluminescence output becomes unstable, and the current threshold for the onset of emission increases in a sample which has been driven to progressively higher currents increases. The process is discussed in terms of a current driven increase in the active volume of highly conducting crystalline pathways in the crystal.