Editing Photoelectric effect (section)

{{short description|Emission of electrons when electromagnetic radiation hits a material}}
{{distinguish|Photovoltaic effect}}
{{Primary sources|date=July 2024}}
[[File:Photoelectric effect in a solid - diagram.svg|alt=|thumb|Photoemission of [[electron]]s from a metal plate accompanied by the absorption of light quanta – [[photon]]s]]
The '''photoelectric effect''' is the emission of [[electron]]s from a material caused by [[electromagnetic radiation]] such as [[ultraviolet light]]. Electrons emitted in this manner are called photoelectrons. The phenomenon is studied in [[condensed matter physics]], [[Solid-state chemistry|solid state]], and [[quantum chemistry]] to draw inferences about the properties of atoms, molecules and solids. The effect has found use in [[Electronics|electronic devices]] specialized for light detection and precisely timed electron emission.

The experimental results disagree with [[classical electromagnetism]], which predicts that continuous light waves transfer [[energy]] to electrons, which would then be emitted when they accumulate enough energy. An alteration in the [[intensity (physics)|intensity]] of light would theoretically change the [[kinetic energy]] of the emitted electrons, with sufficiently dim light resulting in a delayed emission. The experimental results instead show that electrons are dislodged only when the light exceeds a certain [[frequency]]—regardless of the light's intensity or duration of exposure. Because a low-frequency beam at a high intensity does not build up the energy required to produce photoelectrons, as would be the case if light's energy accumulated over time from a continuous wave, [[Albert Einstein]] proposed that a beam of light is not [[Light#Wave theory|a wave]] propagating through space, but discrete energy packets, which were later popularised as [[photon]]s by [[Gilbert N. Lewis]] since he coined the term 'photon' in his letter "The Conservation of Photons" to Nature published in 18 December 1926.<ref>{{Cite book |url=http://www.aps.org/publications/apsnews/201212/physicshistory.cfm |title=December 18, 1926: Gilbert Lewis coins "photon" in letter to Nature |language=en}}</ref><ref>{{cite journal |last=Lewis |first=Gilbert N |date=18 December 1926 |title=The Conservation of Photons |url=https://www.nature.com/articles/118874a0 |journal=Nature |volume=118 |issue=2981 |pages=874–875 |doi=10.1038/118874a0 |bibcode=1926Natur.118..874L |access-date=18 April 2025|url-access=subscription }}</ref>

Emission of conduction electrons from typical [[metal]]s requires a few [[Electronvolt|electron-volt]] (eV) light quanta, corresponding to short-wavelength visible or ultraviolet light. In extreme cases, emissions are induced with photons approaching zero energy, like in systems with negative electron affinity and the emission from excited states, or a few hundred keV photons for [[core electron]]s in [[Chemical element|elements]] with a high [[atomic number]].<ref>{{Cite web|title=X-Ray Data Booklet|url=https://xdb.lbl.gov/|access-date=2020-06-20|website=xdb.lbl.gov}}</ref> Study of the photoelectric effect led to important steps in understanding the quantum nature of light and electrons and influenced the formation of the concept of [[wave–particle duality]].<ref name="serway_1">{{cite book
 |last1=Serway |first1=R. A.
 |year=1990
 |title=Physics for Scientists & Engineers
 |edition=3rd |page=1150
 |publisher=[[Saunders (imprint)|Saunders]]
 |isbn=0-03-030258-7
}}</ref> Other phenomena where light affects the movement of electric charges include the [[Photoconductivity|photoconductive]] effect, the [[photovoltaic effect]], and the [[photoelectrochemical cell|photoelectrochemical effect]].