Relaxation dynamics into two types of luminescence states in C 60 single crystals below 80 K

Abstract

Luminescence spectra from pure C 60 single crystals and their time behavior have been studied in the temperature range below 80 K under the excitation into two distinctive energy ranges. In case of the excitation into the higher-lying band states, two kinds of fluorescence bands, called types A and B, were observed with their onsets at 733 and 684 nm around LHeT. These bands exhibit the anti-correlated temperature dependence, indicating thermally activated population transfer from the initial state of type B to that of type A. On the other hands, the selective excitation into the tail part ( ~ 733 nm) below the fundamental absorption edge stimulates not only a series of Raman lines but also the resonant luminescence which evolves into the type A luminescence with inhomogeneous behavior. It is noteworthy that for just resonance a novel vibronic structure with Δ ~ 120 cm −1 is clearly resolved. The present study strongly suggests that fluctuation in the local intermolecular orientational correlation of molecules is essential to the relaxation processes of photo-excited states in C 60 single crystal.