PHOTOELECTRIC PROPERTIES OF THIN FILMS OF ALKALI METALS

Abstract

Measurements are reported on the color sensitivities of various photoelectric tubes having cathodes made of alkali metals. A composite surface of R-Ag-RO-Ag of any alkali metal R shows a higher sensitivity over a wider range of wave-lengths than R-RO-Ag and has two peaks, one between 330 and 370 mμ, and one at about 500 mμ for potassium and 550 mμ for rubidium and between 700 and 800 mμ for caesium. If a gas filled lamp at 2700°K is used as a light source, photoelectric currents from vacuum photo-tubes are obtained sometimes as large as 29μa per lumen for potassium, and 10–15μa per lumen for rubidium, and 40–50μa per lumen for caesium. It is also reported that the potassium cell in combination with a proper filter would constitute a means for an ideal photometer.