A time resolved study of electrolummescence in fullerene crystals

Summary form only given. Earlier work has shown the ability of fullerene crystals to electroluminesce under DC conditions with a highly nonlinear current-intensity characteristic above a certain threshold voltage [1]. This is similar to the nonlinear phenomena found in the highly excited luminescence and photoconductivity, that are discussed in terms of many body effects [2]. To develop this theoretical model and to investigate the temporal behaviour of electron-hole recombination, measurements of the electroluminescent response of a silver-C60-silver device to triangle and rectangular voltage pulses of different frequencies were performed in the present case. The experiments show the occurence of a phase shift between the voltage pulse and the luminescence signal. This phase shift approaches asymptotically the value of /spl pi//2 with increasing frequency, corresponding to a time delay of about 100 /spl mu/s. In addition an accompanying drop of the luminescence intensity is observable. A theoretical analysis of these processes is proposed, taking into account the dependence of the accumulation and recombination time on the charge carrier concentration.