EFFECTS OF LASER IRRADIATION ON PHOTOLUMINESCENCE OF C-60 SINGLE-CRYSTAL WITH WITHOUT AIR EXPOSURE/

The photo-induced effects of C-60 Single crystals with/without air exp osure have been studied in detail by photoluminescence measurements at 80 K. The laser irradiation onto the sample without air exposure at 8 0 K caused the intensities of the photoluminescence bands to reduce st rongly, e.g. similar to 1/6 for the band at 1.68 eV. The intensities o f the photoluminescence bands were not recovered to the original ones even after the temperature was raised to room temperature. The observa tion suggests that the laser irradiation causes the lowering of the mo lecular symmetry due to the distortion of C-60 molecules. This is cons istent with the results obtained by Raman scattering measurements. On the other hand, the photoluminescence intensity of the 1.68 eV band fo r the sample with air exposure increased with laser irradiation at roo m temperature. The change was reversible at room temperature. The resu lt could be related to the diffusion of oxygen molecules in the C-60 l attice. (C) 1997 Elsevier Science Ltd.