Fundamental Optical Absorption, Electrical Conductivity, and Thermoelectric Power of Calcium Oxide

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Abstract
The opacities of thin backed films of CaO were measured at room temperature over the energy range 5.5 to 11.3 eV. At energies below 6 eV the opacity was low. A sharp peak, attributed to the formation of excitons, was observed at about 7.0 eV. A second strong peak was observed at 8.3 eV. This peak appears to have a doublet splitting of about 0.2 eV and probably should also be ascribed to excitons. Other peaks were observed at higher energies but were less reproducible. The width of the forbidden band was estimated to be near 7.7 eV. The electrical conductivity and thermoelectric power of sprayed aggregates of CaO were measured, as a function of temperature, for several states of activation and were found to exhibit the characteristics of a pore conductor. Using these data and the theory for pore conduction, the electron affinity for CaO was estimated to be 0.7 eV.