Electronic excited states in C/sub 60/ thin film as revealed by luminescence measurement: excitation spectra and temperature dependence

Summary form only given. Important information pertaining to electronic excited states and their relax ation processes in solid C60 can be obtained by the measurement of luminescence and photoconductivity. We have recently succeeded in obtaining a hither to unknown luminescence excitation spectrum of C60 thin film exhibiting well resolved vibronic structures In the optical edge region. These structures can be assigned and compared with a corresponding absorption spectrum showing less resolution. A mirror-image like relationship was established between peaks in the emission and excitation spectrum, indicating a 0-0 transition around 670nm. We also found that the excitation spectrum showed strong peaks at 440-500nm, well corresponding to the solid-state specific absorption structures in the same wavelength region. These peaks exceeded that arising from the allowed transition at 350nm. Another newly found solid-state effect was that an emission intensity vs. temperature curve In 77-450K showed a change of slope at the phase transition point (250-260K), below which luminescence increased more steeply, the first example of an optical property of solid C60 perturbed by the phase transition. Relationship between photoconductivity and luminescence in C60 thin film will also be discussed.