The optical absorption edge of CuO single crystals has been investigated by reflectance and transmittance measurements at different temperatures. An exponential decay of the absorption has been detected, while temperature dependence of the edge and of the steepness between 10 K and room temperature indicate a large coupling of electronic states with lattice vibrations. At the lowest temperatures, excitonic structures have been revealed.

• Received 8 February 1995

DOI:https://doi.org/10.1103/PhysRevB.52.1433