Electron excitation

The next rule follows from the Frank-Condon Principle, which states that the absorption of a photon by an electron and the subsequent jump in energy levels is near-instantaneous.

[8] Under some circumstances, certain selection rules may be broken and excited electrons may make "forbidden" transitions.

The energy and momentum of electrons in solids can be described by introducing Bloch waves into the Schrödinger equation with applying periodic boundary conditions.

The latter page contains a summary of the techniques that are nowadays available for modeling the properties of solid crystals at equilibrium, i.e., when they are not illuminated by light.

The behavior of electrons excited by photons can be described by the quasi-particle named "polariton".

A schematic of electron excitation, showing excitation by photon (left) and by particle collision (right)