ELECTRONIC-TRANSITIONS IN KXC60 (0 LESS-THAN-OR-EQUAL-TO X LESS-THAN-OR-EQUAL-TO 6) FROM INSITU ABSORPTION-SPECTROSCOPY

In situ optical absorption measurements at room temperature are reported for KxC60 (0 less-than-or-equal-to x less-than-or-equal-to 6). The main results are a strong bleaching of the peak at 3.5 eV, an increase and line broadening in the spectral range between 2 and 2.7 eV, an increase of a new structure around 1.3 eV and a strong change for the absorption at 0.47 eV with increasing potassium concentrations. From a fit of the absorption spectra of the three stable phases C60, K3C60 and K6C60 with a Kramers-Heisenberg dielectric function a definite assignment of the electronic transitions was found, which is in excellent agreement with LHS and LDA calculations. The line broadening in the C60 metallic phase is explained as resonating valence fluctuations.