Luminescence methods

Among the more technically demanding, but very sensitive optical methods are procedures that use 'light emitted by the determined substance. Strictly speaking, this would also include flame emission photometry, in which an electron is excited to a higher energy state by a flame and emits light when it returns to a lower energy level. Mostly, however, the electron is excited by radiation (photoluminescence, used in fluorimetry, and phosphorescence), or a substance with an excited electron is created in a chemical reaction (chemiluminescence, used in luminimetry).