Photon emission refers to the process where an atom or molecule releases energy in the form of photons (particles/waves of light).
Excited State: When an electron absorbs energy and moves to a higher energy level within an atom.
Fluorescence: The process where a substance absorbs high-energy photons and then emits lower-energy photons almost immediately.
Luminescence: The general term for any type of light emission from materials that have absorbed energy.