View Full Version : Why is Neodynium Added for Color?
10-31-2001, 10:54 AM
What is it about neodymium that they add it to glass and cz's in order to make them change color in different light? They put it in glass and cut stones out of it called alexandriums. The stones I have are blue in one kind of light and pink in another! The two kinds of light are fluorescent and incandescent, and I can't remember which one causes which color. Imagine my surprise when after buying this weird blue stone and getting it home it was bright pink! I have since found color cz's that do the same thing. Also there is an old-fashioned kind of glassware called by some special name I can't remember, and it is the same shade of weird blue in one light and pure pink in the other!
What is it about neodynium that does this, and wouldn't praseodymium do as well, or some other so-called "rare" earth? How could something in the atomic structure of something make something else change color?
10-31-2001, 12:25 PM
If you want a good book on the physics of color, get Kurt Nassau's The Twelve Causes of Color (actually, I can't remember the number).
It's neodymium that's added to several crystals and glasses. Originally, I believe it was added to welder's glasses to absorb bright IR light that could damage eyes. Later it was found to be laser-active by Elias Snitzer and other folks at American Optical (before they got out of the laser business). It emits light at 1.06 microns, outside of the human visual range in the InfraRed. It has also been made to lase successfully in a variety of incredibly dangerous and corrosive liquids. I've never heard of it being added to crystals just for the color, but it wouldn't be a bad idea. Nd adds a pleasing purple or purple-bluish color.
Neddymium is not used in alexandrite. The active ion in that is Chromium, I believe (not a rare earth). The Alexandrite crystal structure is not isotropic, so you get different colors as you look at it along different directions. Alexandrite looks greenish along one axis, and red along another. It, too, is laser active, producing slightly tunable light in the near IR.
Other rare earths are also laser-active, and are added to a variety of crystals that are identified by annoying, cacophonous acronyms like YAG, YLF, and GSGG.
10-31-2001, 03:25 PM
I know it's alexandrite for beryllium oxide gems, but they really have invented the term alexandrium for the gem made out of glass that has neodymium in it. The gem I bought was cut by a lapidary very sharp and perfect and nice and big and was only 30 bucks. He said it was a kunzite and even supplied a little printed explanation of it that said
it was lithium aluminum silicate with neodymium. But I'm sure it's glass with neodymium in it. At any rate it doesn't look like kunzite even though its shade of pink is somewhat close. They also put neodymium in windows on rocket ships in the space program.
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