What is "photocathode"

n. (context physics English) A cathode that emits electrons when exposed to light

n. a cathode that emits electrons when illuminated

A photocathode is a negatively charged electrode in a light detection device such as a photomultiplier or phototube that is coated with a photosensitive compound. When this is struck by a quantum of light ( photon), the absorbed energy causes electron emission due to the photoelectric effect.