Phosphorescence

Phosphorescence is a specific 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 substances that shone in the dark without burning. Boyle was fascinated by the phenomenon and conducted several experiments using barium sulfide.

Mechanism

Phosphorescence occurs in a manner similar to fluorescence, but with a longer time scale. When a material is illuminated with ultraviolet light, electrons in the material are excited to a higher energy state. In fluorescent materials, these electrons immediately return to their ground state, emitting a photon in the process. In phosphorescent materials, the process is much slower. This is due to the fact that the electrons undergo a "forbidden" transition, meaning that it is statistically unlikely. As a result, the material continues to glow for a period of time even after the light source has been removed.

Applications

Phosphorescent materials are used in a variety of applications. They are used in glow-in-the-dark products, such as toys and clock faces. They are also used in safety and emergency signage. In recent years, phosphorescent materials have been used in television screens and other electronic displays.

See also

• Luminescence
• Fluorescence
• Photoluminescence
• Chemiluminescence

References

Phosphorescence Resources
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