ON THE TEMPERATURE-DEPENDENCE OF THE OPTICAL-ABSORPTION EDGE IN NICKEL-OXIDE

Results are reported of a high-temperature investigation (up to 1000 d egrees C) of the optical absorption edge in NiO. An approximately expo nential dependence of the absorption coefficient on photon energy is o bserved. The absorption coefficient is found to be independent of oxyg en partial pressure, i.e., of native lattice defects. The temperature dependence of the edge gives evidence of strong exciton-phonon couplin g in NiO.