Photoelectric processes in calcium oxide coated cathodes

The spectral sensitivities of photoelectric emission and photoconductivity in probe diodes containing cathodes coated with calcium oxide have been determined over the range of photon energies from 1.4 to 3.1 eV. The two spectral sensitivities are similar in form, showing a rapid rise below about 2.2 eV, followed by a more gradual increase. Structure at about 2.5-2.6 eV is insensitive to the state of thermionic activity of the cathode, and is attributed to the presence of an impurity level at this depth below vacuum potential in the optical energy level scheme. Experiments involving studies of the recovery of photoelectric emission and photoconductivity after oxygen poisoning and of magnetoresistive effects in dark and illuminated conductivity suggest that the greater part of the photoconductivity current is carried by a process of photoelectric emission across the cathode pores. Thermal activation energies have been determined by measurements of the thermionic emission from, and the electrical conductivity of, the cathodes as functions of temperature.