Lyoluminescence refers to the emission of light while dissolving a solid into a liquid
solvent
A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvÅ'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...
. It is a form of
chemiluminescence
Chemiluminescence (also chemoluminescence) is the emission of light (luminescence) as the result of a chemical reaction, i.e. a chemical reaction results in a flash or glow of light. A standard example of chemiluminescence in the laboratory se ...
. The most common lyoluminescent effect is seen when solid samples which have been heavily
irradiated
Irradiation is the process by which an object is exposed to radiation. An irradiator is a device used to expose an object to radiation, most often gamma radiation, for a variety of purposes. Irradiators may be used for sterilizing medical and p ...
by
ionizing radiation
Ionizing (ionising) radiation, including Radioactive decay, nuclear radiation, consists of subatomic particles or electromagnetic waves that have enough energy per individual photon or particle to ionization, ionize atoms or molecules by detaching ...
are dissolved in water. The total amount of light emitted by the material increases proportionally with the total radiation dose received by the material up to a certain level called the saturation value.
Many gamma-irradiated substances are known to produce lyoluminescence; these include
spices
In the culinary arts, a spice is any seed, fruit, root, Bark (botany), bark, or other plant substance in a form primarily used for flavoring or coloring food. Spices are distinguished from herbs, which are the leaves, flowers, or stems of pl ...
,
powdered milk, soups, cotton and paper. While the broad variety of materials which exhibit lyoluminescence confounds explanation by a single common mechanism there is a common feature to the phenomenon, the production of
free radicals
In chemistry, a radical, also known as a free radical, is an atom, molecule, or ion that has at least one unpaired electron, unpaired valence electron.
With some exceptions, these unpaired electrons make radicals highly chemical reaction, chemi ...
in solution. Lyoluminescence intensity can be increased by performing the dissolution of the solid in a solution containing conventionally chemiluminescent compounds such as
luminol
Luminol (C8H7N3O2) is a chemical that exhibits chemiluminescence, with a blue glow, when mixed with an appropriate oxidizing agent. Luminol is a white-to-pale-yellow Crystal, crystalline solid that is soluble in most polar organic solvents but ...
.
These are thus called lyoluminescence sensitizers.
References
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Luminescence