Heterogeneous fullerene thin films as unconventional light emitters

Fullerene thin films can be made to emit broad, intense white light under l aser irradiation by the introduction of heterogeneous structures, unlike th eir homogeneous or pristine state, which only gives very weak luminescence arising from the dipole forbidden transition. The broad spectrum is well fi tted to Planck's formula for blackbody radiation, showing that the emission is of thermal origin. Our previous works showed that inhomogeneous structu res spontaneously formed in C-60/Si layered composite films are involved in this extraordinary properties. In the present study, intentional scratchin g of either composite or pure C-60 films is found to induce similar effects . To gain an insight into the relationships between the thin film structure s and light emission, we measured cathodoluminescence (CL), that is, lumine scence induced by electron beam irradiation, making it possible to assess e missive properties on a microscopic scale. The results show that the format ion of a different phase of carbon as indicated by a change in the CL spect rum is responsible for the emergence of the white light emission. We also f ound that oxygen intercalated in C-60 thin film plays a role in such chemic al modification.