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Fluorescence & Phosphorescence

April 24, 2008

A listener asks: What is the difference between fluorescence and phosphorescence?


The lasting glow of phosphorescence…I’m Bob Hirshon and this is Science Update.

On a previous show, we told you how scientists identify blue diamonds by the phosphorescent glow they emit after exposure to ultraviolet light. This story prompted listener Joules Haglund of Sweden to ask us to explain the difference between phosphorescence and plain old fluorescence. Well, applied physicist Tom Giallorenzi of the Optical Society of America says that both phenomena are caused when photons from a light source excite electrons within certain materials. As the electrons return to a lower energy state, light is emitted. Once the light source is removed, fluorescent materials immediately stop glowing.

TOM GIALLORENZI (Optical Society of America):
This is not the case with the phoshorescent material, because the phoshorescent material stores energy to be released at a later time.

This is why some phosphorescent objects can retain their glow for hours. I’m Bob Hirshon for AAAS, the Science Society.