Phosphorescent

Phosphorescence is a type of photoluminescence related to fluorescence. Unlike fluorescence, a phosphorescent material does not immediately re-emit the radiation it absorbs. The slower time scales of the re-emission are associated with "forbidden" energy state transitions in quantum mechanics. As these transitions occur very slowly in certain materials, absorbed radiation is re-emitted at a lower intensity for up to several hours after the original excitation.

History

The term "phosphorescence" was originally coined by 17th-century chemist Robert Boyle to describe the phenomenon of substances emitting light without burning or without being noticeably heated. Boyle was experimenting with luminescence and a glow-in-the-dark substance known as "Bolognian phosphorus".

Mechanism

Phosphorescence is a process in which energy absorbed by a substance is released relatively slowly in the form of light. This is in contrast to the rapid re-emission of light following absorption known as fluorescence. Whereas fluorescence is a process that only occurs while the absorbing substance is being bombarded with the exciting atoms or molecules, phosphorescence continues for a time after the exciting source has been removed.

Applications

Phosphorescent materials are known for their use in radar screens and glow-in-the-dark toys, whereas fluorescent materials are common in cathode ray tube (CRT) and plasma video display screens, sensors, and white LEDs.

See also

• Luminescence
• Fluorescence
• Photoluminescence

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