OPTICAL-ABSORPTION OF CUGEO3

The absorption coefficient of CuGeO3 was measured in the energy range of 1-4 eV, in a temperature interval between 300 and 20 K, for light p olarized along the b and c crystal axes. A weak absorption band at 1.7 eV is attributed to copper d-d transitions partially allowed by elect ron-phonon interactions; this is followed by a region of transparency leading to a strong exponential edge above 3 eV, which is identified w ith the onset of charge-transfer transitions.