Luminescence in a fluorite or apatite group mineral

Last evening an individual showed me a picture of a specimen that he had purchased in Quilin, China. He said that this specimen was either a fluorite or a apatite group mineral with some rare earth elements in the structure. The curious thing about this specimen, is that it glows in the dark after being subjected to either incandescent light or sunlight. In fact, he said that as the specimen is exposed to the light it starts to glow very quickly and continues to glow for quite some time. Does anyone know anything about these specimens? A quick google search mentions that Europium can cause luminescence in fluorite.

Any other information would be of interest.
Brent Thorne



Edited 2 time(s). Last edit at 11/05/2009 06:38PM by Brent Thorne.

Phosphorescence is common in gypsums, especially those from the Red River Floodway in Canada. In my experience, the phosphoresence is sometimes still visible after 30 seconds or more.

Hi Brent,

Check out

[www.mindat.org]

and

[www.mindat.org]

Frank

Hello Frank,

Thanks for the images. Do you know what the REE is in the fluorite that causes the luminescence? Hopefully someone will know about the fluorites from China.

Brent

I had a combo piece from the Richardson fission mine in Wilberforce ontario. The fluorite and apatite were together in calcite and both fluoresced bright green and kept a glow after being exposed to UV. I've since lost the piece unfortunately

I assume it contained traes of uranium, perhaps REEs, or mineral inclusions that I couldnt see.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A buena hambre no hay pan duro



Edited 1 time(s). Last edit at 11/06/2009 07:32PM by Matt Neuzil.

Hi Brent,

SEM-EDS of a piece of the more luminescent fluorite from the Petrick Pegmatite showed a small amount of yttrium and strontium replacement (<1%), but not much else. These fluorites were irradiated by gamma rays emitted from uranium and thorium minerals in the pegmatite, so most of the luminescence is likely due to color center effects.

Frank

How is charge balance maintained in these minerals when REE replace Ca? Extra F?

I have phosphorescent fluorite as well, from the McGuire pegmatite in CO, another REE locality. Some if it will glow green all night long after being exposed to UV. However not all the fluorite from this locality glows, in fact most doesn't. The non-phopshorescent kind fluoresces orange, if the phosphorescent kind fluoresces orange as well, it is way overpowered by the strong green phosphorescence. The phosphorescent variety is an ugly brownish color, maybe just a hint of purple, the other is mostly green.

The piece that I saw luminesced for twelve hours after it was exposed to sunlight. The individual who had this specimen said the REE's in the fluorite were Europium and Ytterbium. I have done some more research on these specimens and it looks like they can either be natural or they can be manufactured. The individual who had this specimen said that it was natural. I still can not find where they come from in China.

I did a lot of research on the net when I found what my piece would do. Originally I thought normal light or sunlight caused mine to phosphoresce, as well as uv, but upon experimenting with mine, i found that natural light only increased the intensity of the phosphorescence and shortened it's duration, which was also what I read on the net on every sight that mentioned the phenomenon. The shorter wavelengths help knock the atoms down to a more stable level more quickly. It takes a wavelength which is longer(higher energy) than the wavelength which is emitted, to put the atoms in a higher energy state, which is why UV is usually required. I found a green laser pointer would excite it, but the duration was very short compared to uv excitation.

Jim,
You may want to heat a piece of your fluorite to see if it is thermoluminescent similar to Franklins. I found that 1 to 3 minutes in the microwave is sufficient.
-Dean Allum

Thermoluminescent fluorite is a variety called Chlorophane. It is quite popular in China, from what I hear. The Chlorophane that I have (from the US) is thermoluminescent a bright teal color, and is phosphorescent a nice green for several seconds after exposure to SW. I would suggest that you may have chlorophane. Does the specimen in question have any xtal faces? Chlorophane rarely (but on occasion) shows crystal faces.

Put it in water, and in the microwave, and yep, it glows green.

The specimen that I saw was stream tumbled and showed no crystal faces.

Hi Brent,

Pages 213-214 are pretty helpful. [books.google.com]

Ron

Hello,

Eu can occur as +2 and +3. Eu²⁺ can easily substitute for Ca²⁺ in many minerals. So, most of the Eu in Fluorite is +2. Only higher oxygen fugacity leads to a high Eu³⁺ concentration.

I've also read that it is Eu what leads to the green colour of Fluorite (colour center).

Y is a element usually enriched in fluorite. But usually a EDX system is not able to detect the traces of Eu and other REE very well. You need mass spectroscopy to get it.

Regards,
Sebastian Möller



Edited 1 time(s). Last edit at 11/17/2009 08:19PM by Sebastian Möller.

Dear Brent,

it is true that Europium (both divalent and trivalent) can cause luminescence in both fluorites and apatites, but most of the REE has this ability to work as activators of luminescence. Another well-known activator is Mn, but also structural defects are commonly related to luminescence of minerals. Be aware that the concentration of the elements causing luminescence may very well be below the detection limits of standard chemical analytical techniques (down to a few ppm).

As Frank mentions radiation can generate defects (like colour centres), which are often those causing the luminescence explored with thermoluminescence.

Alfredo,
the two main mechanisms for charge balance when REE³⁺ substitutes for Ca²⁺ in apatite are

2Ca²⁺ ↔ REE³⁺ + Na⁺ (basically what you see in the belovite family)
Ca²⁺ + P⁵⁺ ↔ REE³⁺ + Si⁴⁺ (like in britholites)

in addition structural defects can contribute to charge balance and therefore also luminescence.

Henrik