Free and localized excitons in the luminescence spectrum of C60 crystals at high pressure

The luminescence spectra of C₆₀ single crystals are studied at T≅10 K and pressure up to 4.0 GPa. It is observed that as the pressure increases, one fine-structure band in the spectrum intensifies sharply and dominates at pressures P≥1.7 GPa. The pressure shift of this band is much larger than the shift of other bands in the spectrum, and its magnitude correlates with the pressure dependence of the band gap. It is shown that this band could be due to radiative recombination of free Frenkel excitons. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 3, 234–238 (10 August 1998)