OPTICAL GAP OF CUO

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