Heterogeneous fullerene thin films as unconventional light emitters

Fullerene thin films can be made to emit broad, intense white light under laser irradiation by the introduction of heterogeneous structures, unlike their homogeneous or pristine state, which only gives very weak luminescence arising from the dipole forbidden transition. The broad spectrum is well fitted to Planckʹs formula for blaokbody radiation, showing that the emission is of thermal origin. Our previous works showed that inhomogeneous structures spontaneously formed in C60/Si layered composite films are involved in this extraordinary properties. In the present study, intentional scratching of either composite or pure C60 films is found to induce similar effects. To gain an insight into the relationships between the thin film structures and light emission, we measured cathodoluminescence (CL), that is, luminescence induced by electron beam irradiation, making if possible to assess emissive properties on a microscopic scale. The results show that the formation of a different phase of carbon as indicated by a change in the CL spectrum is responsible for the emergence of the white light emission. We also found that oxygen intercalated in C60 thin film plays a role in such chemical modification.