Luminescence
Chemiluminescence
Chemiluminescence is known as the production of light as a result of a chemical reaction. The mixture of chemicals results in the production of a high-energy intermediate, which then breaks down and releases energy in the form of light (photons)
Diagram displays the movement of electrons between shells which results in the emission of energy as photons.
Examples of chemiluminescence
Luminol and Iron
C8H7N3O2 + Fe
Luminol is a powdery compound made up nitrogen, hydrogen, oxygen and carbon.
USE
Luminol is involved in a chemical reaction that is often used in crime scenes, as it reacts with Iron and is able to light up areas that invesigators believe may contain blood.
HOW IT WORKS
Scientists combine luminol with a liquid containing a mixture of hydrogen peroxide, hydroxide and other chemicals. This solution is then sprayed onto areas where investigators believe blood may have been present. If hemoglobin (the protein molecule found in red blood cells) is there, the iron that is present will accelerate a reaction between the hydrogen peroxide and luminol. In this reaction, luminol loses both nitrogen and hydrogen atoms and gains oxygen atoms. This change in make-up creates a molecule called 3-aminophthalate, where the electrons in the oxygen atoms are changed to higher orbitals, but quickly fall back to a lower state, which releases the extra energy as light photons.
Diphenyl Oxalate and Hydrogen Peroxide
C14H10O4 + H2O2
Diphenyl Oxalate and Hydrogen Peroxide are a combination of chemicals that react to form one of the most popular chemiluminescent reactions of all time.
USE
The reaction of diphenyl oxalate and hydrogen peroxide is commonly seen in the recreational use of glow sticks.
HOW IT WORKS
Although glow sticks appear to contain only one chemical, they actually contain 2 different chemicals in seperate sections. Inside in the tube there is mixture of diphenyl oxalate and a fluorescent dye (to give the colour of the glow stick). Floating inside that mixture is a glass tube that contains a solution of aqueous hydrogen peroxide. When the user bends the glow stick, the glass tube breaks and causes the two solutions to react. This reaction produce two molecules of phenol (C6H6O) and one molecule of 1,2-dioxentanedione (C2O4) which decomposes to create two molecules of CO2, simultaneously releasing energy. This energy is absorbed by the dye, which excites it to a vibrational state before relaxing back to its ground state, when it releases energy as a photon of light.
Nitric Oxide + Ozone
NO + O3
The reaction gaseous reaction of nitric oxide and ozone has proven itself useful in a huge way over time.
USE
Nitric Oxide and Ozone reactions are used to test environment air-quality. This reaction determines the concentration of nitric oxide within the air.
HOW IT WORKS
When nitric oxide and ozone are combined it produces nitrogen dioxide (NO2) in an excited state, and oxygen gas (O2). The excited nitrogen dioxide drops back to a lower energy state which releases light that is visible to infrared technology. Photomultipliers are then used to count the amount of photons which will be proportional to the number of nitric oxide molecules present. This information allows them to determine the concentration of NO based on the volume of gas tested.