From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.chem
Subject: Re: Glow-in-the-dark chemicals/mixtures
Summary: Phosphorescence and chemiluminescence
Keywords: phosphorescence, chemiluminescence
Date: 26 Mar 91 04:25:03 GMT

In article <16034.27ea0d06@levels.sait.edu.au>
yaadmin@levels.sait.edu.au writes:

>What are the chemicals used to create "glow-in-the dark" products?
>The kind that you expose to a light source to charge them up and then they
>emit a green glow for a while, but not really bright enough to be useful
>as a light source.
 
	You are referring to phosphors (the material) and phosphorescence
(the characteristic).  The useful lifetime of such phosphorescence for
paints is on the order of hours.
 
	Most phosphorescent paints use inorganic crystal phosphors,
which are usually mixtures of metallic sulfides and/or oxides.  Other
metals, such as bismuth and copper, may be added as "activators".
 
	A typical green phosphor found in "luminous paint" is a mixture of
zinc sulfide and cadmium sulfide.  The resultant emission spectrum shifts
toward longer wavelengths as the percentage of cadmium sulfide in the
mixture is increased.  Persistence (i.e., phosphorescence lifetime) of
such mixtures range from 1 to 10 hours.
 
	A typical blue phosphor found in luminous paint is a mixture of
calcium sulfide and strontium sulfide.  Persistence may be as long as 12
hours.
 
	In general, as the emission wavelength of a phosphor increases
(i.e., shifts toward red), persistence decreases.  While yellow and red
phosphors exist, they are not common because of the short persistence.
Cadmium sulfide, in fact, has emission energy in the near-IR region.
 
>Also, does anybody know why they only seem to come in green...I have never
>seen red or blue or....etc
 
	See above reason for lack of persistence at red wavelengths.
Blue pigments are not as common as green since the human eye is much more
sensitive to green wavelengths.
 
>The other kind of luminous stuff is in light sticks. (A plastic tube
>containing two chemicals - one in a glass vial - which you have to
>bend to break the glass and shake.)  The resulting chemical reaction
>emits a very bright glow for ~2-3 hrs.  I have seen these in green and blue.
 
	You are probably referring to the chemiluminescent lightsticks
manufactureed by American Cyanamid under the tradename "Cyalume".  While
I don't know the exact ingredients in the Cyalume product, I can give
you a clue.
 
	Chemiluminescence is exhibited by many cyclic hydrazides when such
are oxidized in the presence of a strong base.  The resultant light is
emitted due to excitation of the amino-phthalate dianion.  The most
common example of a suitable cyclic hydrazide is o-aminophthalylhydrazide
(I'll pass on the IUPAC for the moment), better known as luminol.
 
	The luminol loses the hydrogens from the hydrazide groups due to
the -OH radicals from the strong base.  The oxidizing agent knocks out
the nitrogens (liberating elemental nitrogen), destroying that ring, and
creating the amino-phthalate dianion.
 
Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
VOICE: 716/688-1231       {boulder, rutgers, watmath}!ub!kitty!larry
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