fotoelektrische

Fotoelektrische, or the photoelectric phenomenon, denotes the emission of electrons from a material, typically a metal surface or a suitable semiconductor, when it absorbs light. The effect provided pivotal evidence for the quantum nature of light and has been exploited in a range of detectors and energy devices.

In its ideal description, emission occurs only when the incident light has a frequency above a threshold determined by the material’s work function φ. The kinetic energy of emitted electrons is given by E_k = h f − φ, where h is Planck’s constant and f the light frequency. The emission rate increases with light intensity above threshold, while the maximum kinetic energy depends mainly on frequency rather than intensity.

Historically, the effect was observed by Philipp Lenard and explained by Albert Einstein in 1905, introducing the concept of photons. Einstein’s theory provided substantial support for quantum theory and earned him the Nobel Prize in Physics in 1921. The photoelectric effect is distinct from, but related to, the photovoltaic effect in semiconductors, which generates electrical energy without ejecting electrons into vacuum.

Applications include photoelectric detectors, photomultiplier tubes, and vacuum phototubes used in early instrumentation, as well as photovoltaic cells and light sensors. The study of the photoelectric effect remains central to quantum electrodynamics and the broader understanding of light–matter interactions.