CHAPTER XIII 



CHEMILUMINESCENCE 



Introduction 



THIS TYPE of luminescence requires no previous exposure to radia- 

 tion of any kind, no gentle heating, and no mechanical excita- 

 tion. The energy for light emission comes from a chemical reaction, 

 usually involving considerable change in the composition of the 

 chemiluminescent material. The reaction may occur in gas phase 

 or in a liquid. The so-called " cold flames " of ether or carbon 

 disulphide or metal vapors in contact with oxygen or halogens are 

 examples of gaseous chemiluminescence. The various flame reac- 

 tions called pyroluminescences, the yellow of sodium, green or blue 

 of copper salts, etc., in the Bunsen flame are additional examples of 

 gas reactions, at one time regarded as chemiluminescences connected 

 with recombination of ions to molecules or change of monovalent 

 to bivalent ions. They are sometimes called indirect chemilumi- 

 nescences to distinguish them from the direct chemiluminescences, 

 where actual splitting of a molecule occurs. The observation of 

 these colors is as old as alchemy itself.^ 



The outstanding example of a gaseous chemiluminescence is the 

 glow of solid phosphorus in air. When dissolved in organic liquids 

 or as a colloidal solution in water, phosphorus does not luminesce; 

 the light of a solution comes only from a gaseous layer near its 

 surface or from bubbles of air in suspension. Chemiluminescence 

 which accompanies oxidation of organic compounds dissolved in a 

 liquid is a much later discovery, connected with the spectacular 

 development of organic chemistry in the late nineteenth century. 



^Vannuccio Biringuccio (1480-1539?) of Sienna, in his De la pirotechnia (Venice, 

 1540) , translated by C. S. Smith and M. T. Gnudi (New York, 1942) , used the color 

 of flame to identify metals. He wrote: " on a well burning fire it [ore and lye] 

 develops the color of the fumosities which issue from it." E. Mariotte (1688) cited a 

 number of green flames and Thomas Melvill in 1752 called particular attention to 

 the yellow color of sodium. His account was published in 1756. David Brewster intro- 

 duced the monochromatic sodium lamp in 1822. 



423 



