PhotoElectric

Photoelectric is an adjective used to describe phenomena and devices in which light interacts with matter to produce or influence electric charge. The most studied example is the photoelectric effect, in which electrons are ejected from a material, typically a metal, when illuminated by light with sufficient energy. The effect was first observed by Heinrich Hertz and explained by Albert Einstein in 1905, introducing the concept of photons and the quantum nature of light.

In the external photoelectric effect, emission occurs only if the photon energy hν exceeds the work function φ of the material. The number of emitted electrons generally increases with light intensity up to a saturation point, while the maximum kinetic energy of the emitted electrons rises with frequency above threshold. The phenomenon provided crucial evidence for quantum theory and remains a standard tool for probing surface properties and electron dynamics.

Photoelectric-based devices include photoelectric cells (photocells), photodiodes, and photomultiplier tubes, which detect light by inducing photoemission or photo-induced current. These sensors are used in automation, safety systems, measurement instruments, and display technologies. The term is sometimes used in broader contexts to describe light-induced electronic effects in solids.

The photoelectric effect is distinct from the photovoltaic (solar cell) effect, which converts light into electricity via semiconductor processes without emission of electrons into a vacuum. Both concepts are central to the study of light–matter interactions and optoelectronic applications.