Photoelectric Properties of Lead Sulfide in the Near and Vacuum Ultraviolet

Measurements of photoelectric yield and electron energy distribution have been made on natural crystals of lead sulfide, Peruvian galena, in spherical photocells at pressures of 10^-8 mmHg. Under these conditions maximum yields are found to be of the order of 1% in contrast to the much higher yields previously reported for this material. Yield data for cesium-coated samples are also presented, as are values of the optical absorption coefficient in the range 4-12 eV. Observed effects are interpreted as indicating the existence of an additional valence band whose maximum is located approximately 4 eV below the top of the higher bands. Such an assignment is found to be in qualitative agreement with the computed band structure.