Lyoluminescence
Encyclopedia
Lyoluminescence refers to the emission of light while dissolving a solid into a liquid solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...

. It is actually a form of chemoluminescence
Chemoluminescence
Chemiluminescence is the emission of light with limited emission of heat , as the result of a chemical reaction...

. The most common lyoluminescent effect is seen when solid samples which have been heavily irradiated by ionizing radiation
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...

 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 lyoluminesce; these include spices, powdered milk
Powdered milk
Powdered milk is a manufactured dairy product made by evaporating milk to dryness. One purpose of drying milk is to preserve it; milk powder has a far longer shelf life than liquid milk and does not need to be refrigerated, due to its low moisture content. Another purpose is to reduce its bulk for...

, 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 solution. Lyoluminescence intensity can be increased by performing the dissolution of the solid in a solution containing conventionally chemoluminescent compounds such as luminol
Luminol
Luminol is a versatile chemical that exhibits chemiluminescence, with a striking blue glow, when mixed with an appropriate oxidizing agent...

. These are thus called lyoluminescence sensitizers.

The idea that free radicals underlie the production of light was confirmed in a paper (title: "Lyoluminescence characteristics of trehalose dihydrate") published in the journal Applied Radiation and Isotopes in 2001 by a group at the Bhabha Atomic Research Centre in Trombay, Mumbai
Mumbai
Mumbai , formerly known as Bombay in English, is the capital of the Indian state of Maharashtra. It is the most populous city in India, and the fourth most populous city in the world, with a total metropolitan area population of approximately 20.5 million...

, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

.
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