Chemiluminescence

            Chemiluminescence is a general process that consists of a reaction that produces molecules that become excited and release light.  Some reactions that might have fluorescent or phosphorescent properties can also fall under the category of chemiluminescence.  This property is very broad.  All it involves is two molecules reacting to produce energy.  This energy excites the product of the reaction.  The excited molecule either releases a photon or transfers its energy to another molecule for emission.  Bioluminescence is a subcategory of chemiluminescence.  This process is how fireflies glow (7).

  One of the earliest studies of chemiluminescence was by Henry Brand.  This German alchemist was attempting to obtain gold from human urine.  Instead, he obtained phosphorous that glowed in the air.  This glowing was due to chemiluminescence.  Luminol is a chemical that is used in devices to measure nitrogen dioxide in the air.  Nitric oxide and ozone react together in a chemiluminescent reaction.

NO + O₃ = NO₂* + O₂

NO₂*= NO₂ + hv

In this reaction, nitric dioxide is produced in an exited state denoted by the asterisk.  This excited molecule emits a photon and completes the chemiluminescent reaction, which has about a ten percent yield.  This reaction was used in the 1970’s for detecting harmful nitric oxide exhaust in cars. Putting dry air through electric discharge easily creates ozone.  In these automobile tests, the sample exhaust and the ozone were mixed to create light.  This light was then amplified then measured.  The amplification allows for a broader range of samples of exhaust to be measured (7). 

            Glow sticks depend on chemiluminescence.  The U.S. Navy first developed them for stealth missions.  These sources of light are easily shielded if darkness is necessary. With this new technology, the U.S. Navy dropped behind enemy lines undercover.  Divers in murky waters also use these light sticks extensively (7). 

2H⁺ + C₂O₄^2- +H₂O₂ = 2CO₂ + 2H₂O

Hydrogen peroxide (H₂O₂) reacts with oxalate ester (C₂O₄^2- ) to produce two carbon dioxide (2CO₂) molecules, water, and energy.  This energy produced by the exothermic reactions is transferred to a fluorescent dye, which emits this energy as light.  The fluorescence makes the stick “glow.”  Another example of chemiluminescence at work is when metals glow blue when they get really hot.  However, the yellow flame from burning wood is not chemiluminescence.  Chemiluminescence is present in blacksmith’s shops all the way to the great depths of the ocean (7).