X-ray fluorescence is the process in which photons emitted from an x-ray radiation source cause photoelectric fluorescence in a sample. When primary X-rays is illuminated to a sample, it excites the atoms. This causes ionization and ejecting electrons from the inner (usually K and L) energy orbitals. The ejected electrons are replaced by electrons from the higher energy orbitals. When this happens, secondary energy is released due to the decreased binding energy of the inner electron orbital compared to the outer one. The energy emitted is characteristic to the type of atom involved. Due to this characteristic transition between specific electron orbitals of an element, the resulting fluorescent X-rays can be used to quantify the elements that are present in a sample.
