Temperature dependence of the photoluminescence in polymeric solidC60

Photoluminescence (PL) spectra of several polymeric phases of solid ${\mathrm{C}}_{60}$ synthesized under high pressure and high-temperature conditions have been studied in the temperature range between 300 and 15 K. The PL spectra of polymerized ${\mathrm{C}}_{60}$ show significant redshift and broadening relative to the PL spectrum of pristine ${\mathrm{C}}_{60}.$ Results on photopolymerized ${\mathrm{C}}_{60}$ films are also presented for comparison. A peak at 1.75 eV in the room temperature PL spectrum is found to be a characteristic of the rhombohedral phase. This peak is moderately strong at 300 K and disappears below 100 K in contrast to the behavior of other PL peaks, particularly the emission at about the same energy in pristine ${\mathrm{C}}_{60}.$ The 1.75 eV PL peak is absent at all temperatures in the photopolymer and in the orthorhombic phase. Our results show that the room temperature PL spectra and the temperature dependence of the PL can be used to distinguish the various polymeric phases.