Growth and photoluminescence spectra of C60 single crystals

Photoluminescence spectra of large size (about 0.5 cm) C-60 single crystals grown by vapour-transport technique in a sealed quartz ampoule, have been measured from 10 to 300 K. The main feature of the PL spectra is the splitting effect of the emission lines, related to the presence of two different molecular orientations. The zero-phonon line (ZPL) is observed, together with its phonon replicas. The ZPL is attributed to a self-trapped polaron exciton of intramolecular Frenkel type, typical of molecular crystals, in the singlet state. The relative triplet state is observed and its phonon replicas are located at lower energy. On the high-energy side of the ZPL two structures attributed to X-trap recombinations are present at low temperatures and they disappear at higher temperatures. (C) 1998 Elsevier Science B.V. All rights reserved.