Chemiluminescence

Chemiluminescence (or Chemoluminescence) is a kind of luminescence. It is a process of making light from a chemical reaction. Chemiluminescence in biological systems is called bioluminescence. 

The light made in chemiluminiscence is not directly related to heat. A simple two step example of a reaction of A, and B, that produces; C, D, and light.
[A] + [B] → [C*] + [D]
[C*] → [C] + Light 
C* is an excited state of C. 

This reaction is simpler than most chemiluminesence reactions. The excited state happens when electrons are pushed into a  higher orbit by the energy of a chemical  reaction. The excited state is less stable than the ground state. The electrons in the excited state fall to the ground state (lower energy), emitting light. 

The amount of measurable light made is called radiant intensity: ICL (photons emitted per second). 

 Analytical applications
The device needed to measure the light made is simple. It needs something to hold the sample, and a photomultiplier tube. There are three ways for this to be used in chemical measurements. 
sometimes the product wanted makes light when it reacts with another compound, 
in another type the amount of light made drops when the wanted product is added, 
sometimes the wanted product when added to a chemiluminescence reaction makes more light(a catalytic reaction).

 Analysis of gases 
The method measures small amounts of atmospheric pollutants. A common method measures the amount of nitrogen monoxide by reacting it with ozone. The light made has a wavelength range of 600 to 2800 nm.

 Analysis of liquids 
Luminol is the most well known type of compound used for chemiluminescence in liquids. 

 Analysis of cell organelles 
Ca2+(calcium) inside of different parts of cells like the mitochondria can make light when it reacts with a protein from jellyfish named aequorin. Nitric oxide(NO) is in cells and is a way for cells to talk to each other, this can be measured with the compound luminol. 

Other examples
An example of chemiluminescence molecules in nature is firefly luciferin.
The process is used to make glowsticks.

References

Daniel C. Harris. In Quantitative Chemical Analysis Seventh Edition: 2007 by W.H. Freeman and Company.
Douglas A. Skoog, James F. Holler, Stanley R. Crouch. In Principles of Instrumental Analysis Sixth Edition:2005 by Thomson, Brooks, Cole.

Category:Chemical reactions
Category:Light sources