Photothermal deflection spectra of crystalline C60Sx and RbC60 Original Research Article

The optical absorption spectra of C60, C60Sx single crystals and polymerized crystalline RbC60 in the weak-absorption region (from 0.6 to 2.3 eV) have been measured by photothermal deflection spectroscopy (PDS). The optical energy gaps, Eopt, corresponding to optically forbidden transitions of weak absorption, were derived from Tauc plots as 1.63 and 1.72 eV for the single crystal C60 and C60Sx, respectively. The weak-absorption characteristics of crystalline C60, C60Sx and RbC60 are discussed. With respect to pristine C60, the absorption edge of the single crystal of C60Sx shows a blue shift of about 0.1 eV, indicating that C60 is electronically isolated in this compound. The absorption edge of polymerized RbC60 crystal, however, red-shift significantly in PDS, implying that there is electronic interaction between the host C60 molecules and the guest Rb atoms.