fotoelektronisk

Fotoelektrisk refers to processes in which electrons are ejected from a material after absorption of light. In solids this includes the photoelectric effect at metal surfaces and related photoemission phenomena. When light of frequency ν shines on a material, photons carry energy hν. If hν exceeds the material’s work function φ, an electron can be emitted. The maximum kinetic energy of the emitted electron is KEmax = hν − φ, and the number of emitted electrons grows with light intensity, provided the frequency is above threshold. Emission is not observed below the threshold frequency.

Historically, the phenomenon was first observed by Hertz in 1887 and explained by Albert Einstein in 1905, who introduced the concept of light quanta and formulated the relations E = hν and KEmax = hν − φ. Einstein’s explanation helped establish quantum theory; he received the Nobel Prize in Physics in 1921 for this work.

There are external photoelectric effects (emission from a surface) and internal photoelectric effects in semiconductors. Photoemission spectroscopy uses measurements of the kinetic energy and angular distribution of emitted electrons to study electronic structure and surface properties.

Applications include photodetectors, photoelectric sensors, and photocathodes in vacuum tubes; related technologies underpin photovoltaic devices and certain imaging sensors.