Photoelectric Emission from Barium Oxide

Abstract

Photoelectric emission measurements were made on sprayed coatings of BaO in several states of thermionic activity and at different temperatures. The yield from active cathodes shows a rise at a quantum energy of 3.8 ev ascribed to exciton-induced emission and another rise at 5 ev attributed to electrons ejected from the filled band. A magnetic velocity analyzer was used to determine the energy distribution of emitted electrons. The data indicate that the emission at low quantum energies arises primarily from direct ionization of impurity levels located photoelectrically about 2 ev below the vacuum level. For higher incident quantum energies, where exciton-induced emission is expected, a new energy distribution appears which peaks at very low energy. This peak does not shift with increasing $h\nu$ and is similar to the slow-group distribution observed in the alkali halides.