Photothermal deflection spectra of crystalline C60Sx and RbC60

The optical absorption spectra of C-60, C60Sx single crystals and polymeriz ed crystalline RbC60 in the weak-absorption region (from 0.6 to 2.3 eV) hav e been measured by photothermal deflection spectroscopy (PDS). The optical energy gaps, E-opt, corresponding to optically forbidden transitions of wea k absorption, were derived from Tauc plots as 1.63 and 1.72 eV for the sing le crystal C-60 and C60Sx, respectively. The weak-absorption characteristic s of crystalline C-60, C60Sx and RbC60 are discussed. With respect to prist ine C-60, the absorption edge of the single crystal of C60Sx shows a blue s hift of about 0.1 eV, indicating that C-60 is electronically isolated in th is compound. The absorption edge of polymerized RbC60 crystal, however, red -shift significantly in PDS, implying that there is electronic interaction between the host C-60 molecules and the guest Rb atoms. (C) 2000 Elsevier S cience Ltd. All rights reserved.