What makes glow-in-the-dark stuff glow?
Q:  In the old days radium was used to make
watch dials that would glow. Today we have a
million things from the plastic stars on my
daughter's ceiling to the watch on my wrist that
will give off light long after they are exposed to
light. What material now makes all these things
glow?
[© 1997 Charles Hoberman, used by permission] The glow-in-the-dark
Hoberman Mini Sphere.
A: The material is called phosphor. It has atoms with
a peculiar property: Shine visible light on a phosphor
and you excite the electrons in its atoms so they jump
to a higher energy state. They have enormous
difficulty radiating energy as light. So the excited
electrons stay there at the higher statestuck--for as
long as several hours. If you quit exciting the
electrons by turning off the light, then the electrons
eventually return to their original state by emitting
light. They glow in the dark. Toy makers commonly
use two phosphors: Zinc Sulfide and a newer one that
glows much longer, Strontium Aluminate.
Further Surfing:
How things work by Louis A. Bloomfield, University of Virginia
How stuff works by Marshall Brain
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