Density of Color Centers in Barium Oxide as a Function of the Vapor Pressure of Barium

Single crystals of barium oxide were exposed at a temperature of 1423°K or 1473°K to barium vapor of different pressures ranging from 3.4×10−5 mm Hg to 7.6×10−2 mm Hg. The resulting blue coloration was measured in an absorption spectrometer, which provided estimates of the number of color centers per cm3, NF. The relation between NF and the number of barium atoms per cm3 in the vapor, Nv, was NF=1.5×1013Nv13. This relation can be tentatively explained by assuming total dissociation of the color centers into oxygen vacancies and free electrons at the temperature of formation.