A photocathode's a negatively charged electrode in a light detection device such as a photomultiplier or phototube that's coated with a photosensitive compound. When this's struck by light, the absorbed energy causes electron emission due to the photoelectric effect. Coatings Although a plain metallic cathode will exhibit photoelectric properties, the specialized coating greatly increases the effect. A photocathode usually consists of alkali metals with very low work functions. The coating relea… (More on Photocathode)