Spontaneous emission and photon release describe a fundamental radiative transition mechanism wherein an isolated quantum system decays from a higher energy eigenstate to a lower one without external perturbation, resulting in the stochastic liberation of electromagnetic radiation quanta known as photons. The process is governed by Fermi's Golden Rule within Quantum Electrodynamics, defining the emission rate via interaction Hamiltonians and density-of-states factors inherent to free space vacuum fluctuations. This principle constitutes the foundational decay mechanism for excited states across atomic, molecular, optical physics, and solid-state spectroscopy domains.
Prerequisite chain context: requires Absorption Process for Electron Excitation.