Properties of Electronic Excited States of C₆₀ Thin Films as Seen from Photoconductivity and Luminescence Behavior: Dependence on Excitation Wavelength and Temperature

N. Minami, S. Kazaoui, and R. Ross
[Mol. Cryst. Liq. Cryst., Vol.256, p.233, 1994]

Photoconductivity and its temperature dependence have been measured for both oxygen-exposed and nonexposed C₆₀ thin films. A constant activation energy for different wavelengths, together with the insensitivity of luminescence emission spectrum to excitation energy, suggest a molecular excitonic nature of solid C₆₀'s electronic states. Luminescence excitation spectra show that emission efficiency is higher for the excitation of forbidden states than allowed states. A turning point at 250-260K has been found in a luminescence vs. temperature curve and is discussed in relation to the phase transition from fcc to sc.