Unusually broad and intense photoluminescence from morphologically modified C60 films

As an attempt to develop novel optically functional materials, C60Si layered composite was prepared by the alternate repetition of the thermal evaporation of C60 and the sputtering of Si. For the Si content higher than 0.5wt%, we found that under Ar ion laser excitation (514.5nm) the composite demonstrated strong white photoluminescence that could be seen by the naked eye. Its emission spectrum, after the correction for the detection system, was shown to increase monotonically from the visible to near infrared (up to 1.5μm) without any specific spectral features. For the lower Si content, the photoluminescence was weak and peaked around 750nm resembling that of pristine C60 films. The spectral shape analysis of the white luminescence based on the Planck distribution gave good fit and yielded surprisingly high black-body temperatures of 1400–1600K. The fact that the replacement of the Si layer with other sputtered materials gave essentially the same results suggests that factors essential to this phenomenon are the C60 layer and its modification induced during the process of sputtering, but not the Si layer. We discuss the present results in terms of similarities and differences with the previously reported white luminescence from C60 powder or crystallites and their implications are considered.