fotoelektrisen

Fotoelektrisen refers to phenomena related to the emission of electrons from a material, typically a metal or semiconductor, when it is illuminated by light. The most studied aspect is the external photoelectric effect, where photons deliver energy to bound electrons, enabling their ejection into vacuum. The process depends on the photon energy relative to the material’s work function, the minimum energy required to liberate an electron from the surface.

The basic relation is E = hν, where h is Planck’s constant and ν is the light frequency. An emitted electron can have kinetic energy KEmax = hν − φ, with φ representing the work function. If hν ≤ φ, no emission occurs. In addition to energy thresholds, the emission rate increases with light intensity up to a saturation current, where all accessible electrons at the surface are being emitted. The threshold frequency ν0 = φ/h marks the cutoff below which photoelectric emission does not occur.

Historically, the photoelectric effect provided crucial evidence for the quantum nature of light. It was first observed by Heinrich Hertz and later explained by Albert Einstein in 1905, a cornerstone in quantum theory for which Einstein received the Nobel Prize in Physics in 1921.

Variants of the phenomenon include the internal photoelectric effect, or photoconductivity, where light excites electrons within a solid, altering its electrical conductivity rather than causing emission into vacuum. Practical applications include photodetectors, photocathodes in devices such as vacuum tubes and image sensors, and various light-sensing technologies. Ongoing research explores photoelectric processes in novel materials and surfaces, with implications for sensors, energy conversion, and surface science.