Jablonski diagram:

Chemiluminescence is other phenomenon which falls in the category of luminescence. This refers to the emission of radiation in during a chemical reaction. Thus, in such cases the excited state is not a result of absorption of electromagnetic radiation. An oxidation of luminol (3-aminophthalhydrazide) in an alkaline solution is an instance of chemiluminescence.  An aqueous solution of luminal is oxidised through a solution of sodium chlorate (commercially available bleaching powder) and gives out a blue glow without rise in temperature. Luminol is oxidised to aminophthalate ion that is generates in an excited state and emits blue light on dropping to the ground state. The reaction could be written as below.

The processes included in the excitation through radiation and the radiative emissions can be understood along with the help of Jablonski diagram. Now let us learn about Jablonski diagram and see how it elaborates the phenomena of fluorescence and phosphorescence.