Photoemission is the ejection
from the surface of a material (metal) caused by an increase of energy, such as a photon
of light of sufficiently high frequency striking the surface. The inbound photon must have a frequency high enough such that it's energy, given by
where h is Planck's constant
and f is the frequency
, is high enough so that an electron in the valence band
can overcome the metal's work function
and be ejected.