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[Parvin]

What makes calcite fluoresce blue under short wave? What trace element? What impurity?

[Mike Wood]

I have read (maybe an outdated source) that 'Iceland Spar' (presumably from Iceland?), sometimes shows a 'dull, blue luminescence' which was thought to have been caused by defect centres in the crystal lattice.
Calcite normally fluoresces yellow/orange/red and is usually caused by a small amount of Mn2+ substituting; in the range of a few hundred to a few thousand ppm. Apparently some REE such as Dy3+ and Sm3+ substituting in small amounts can produce a very similar colour range.
However, this info is over 25 years old and it is very likely there are more explanations available these days!
Mike

[Pete Modreski]

And, my understanding is that it is high Europium (Eu2+) that causes the blue fluorescence.

Pete

[Mark Ost]

Calcium is not intrinsically fluorescent and requires activators such as Uranium or Europium. I have the typical red fluorescing calcite, but also green, more rare due to uranium content, and some yellow. My Icelandic spar shows no trace of color or afterglow under any frequency of UV.

[Parvin]

Hi Pete,

I have tried to use Eu+2 in order to make calcite fluoresce blue, but it didn't work out. Also, Eu is very expensive, Do you have any idea like what other activators cause calcite emits blue color?
Thanks so much.

Parvin

[Rei]

Parvin: What exactly are you doing with europium? Just dipping the calcite in it? Colors are due to small amounts of impurities in the crystal lattice (or defects in the lattice) - they're not surface treatments.

For what it's worth, I find a lot of massive calcite on my land in Iceland, and I've never found a specimen that fluoresces under UV (I've tried two frequencies). I always do my tests in the laundry room, and bleached white socks kick off a lot more glow than my calcite ;)

Sometimes a specimen just is what it is. There are all sorts of ways you can handle specimens, and sometimes they can make a world of difference. But a lot of things about a piece just can't be changed. If you want to make glowing calcite rather than finding it, you're going to need to grow it from scratch. Or paint it with glow-in-the-dark paint. ;) Hey, if you wanted to shell out the money you could use tritium paint, that'd be pretty awesome - it'd look like something straight out of a comic book ;)

[lluis]

Hi, Parvin

For what I found, blue color seems due to Eu2+ and Eu3+, acting cerium as activator....
So, probably you should use the three elements

Maybe you find this article interesting for your purposes....
https://www.fluomin.org/galeriespectre/spectre.php?lg=fr&name=CALCITE
(link normalized by FMF)

With best wishes

Lluís

[Josele]

[Parvin]

Thanks, I will do.

[Parvin]

Josele,

So, you are saying that even with those three activators, it won't be possible to get the blue color? At what wavelength we should see the blue color?
Thanks.

Parvin

P.S. I am mixing the Eu doped in solution of chloride with ammunium carbonate in order to precipitate calcium carbonate.

[lluis]

Hi, Josele

I am not in fluorescence... Just chemist...

But, even with what you say, seems that in the article the blue calcite has the two states Europium. And the cerium.
Cerium is just the activator: it absorbs UV and transmits energy to Europium...
No color, no fluorescence... Just transmitting energy from UV to Eu... So, no Ce, no fluorescence....

Hi, Parvin: if you use only Eu, without activator, maybe you would not see fluorescence because no energy is transmitted to Eu.
By the way, the precipitation, seems that should be done at 70ºC, and precipitate should be treated thermally (in one I read at 1000ºC in CO2 atmosphere....).
Then, maybe you simply do not fit the required conditions....: thermal treatment and activator...

With best wishes

Lluís

[Parvin]

Hi Lluís,

Could you please tell me what article you are exactly referring?
Thank you.

Parvin

[Josele]

Will see blue color when emission is in 450 - 500 nm range

In the abstract of the cited article about blue luminescence you can read: ... Both centers have spectral-kinetic properties very unusual for mineral luminescence, which in combination with extremely low impurity concentrations prevent their identification with specific impurity related emission. The most likely explanation of these observations may be the presence of radiation-induced luminescence centers.
If Michael Gaft doesn't know it, who knows it?

I'm curious of a more detailed explanation of your system to obtain doped calcite.
Can you describe the procedure? Did you get any results? Can you post some photos here?

[lluis]

Parvin, the article is the one that I placed in my first message...
Long, besides.

Josele: Don is as human as us. He could be right...or he could be wrong.
In complex theory, were many, till last that seems right. Were the predecessors wrong? No, they just didn't have all the info.
When the wave function was generated by Schrödinger, Bohr said that it was the reality, and Einstein said that it was a way to explain reality....
As many heads, as many huts....

Anyway, I am fond to remember that a young lady was the one that showed that skeletal galenas were fake...when they have been sold by many seasoned experts....

So...

For colors..: Pt uses to be slightly yellow and with chloride ions, strong brown. But a cis-platinum is green..... (complex theory....).
Europium could be whatever. But if in calcite, in the right place, it creates the blue fluorescence.... As I said, if not wrong in such article, a blue fluorescent calcite had Eu2+, Eu3+ and cerium (as activator).
More.... Pb is in color...But amazonite is green due to Pb (color centers due to faults in crystal net due to different sizes....)
Then, nothing surprises me..... : things are and explanations, well, our work (the humans work, I mean)

With best wishes

Lluís

[Josele]

I've been checking all calcites in my collection looking for a blue fluorescence, without result. About a third part showed a significant fluorescence. In this benchmarking of some representative specimens, we can see a small part of the diversity of luminescence in calcite, due to different activators, co-activators and combinations, and this gives an idea of the complexity.

[Pete Modreski]

Josele, that's a nice assortment of calcites and a nice photo of them.

So, as you probably know, the blue-fluorescing calcite is very much the exception among calcites, even among fluorescent calcites. We often call it "Terlingua-type" calcite, and it has the unusual suite of properties of blue fluorescence SW, pink LW, and very bright and long-lived phosphorescence after the SW exposure. And there are only a few known localities where calcite with these properties occurs; the main ones being Terlingua TX, one locality in Mexico, and Hope, Indiana (there may be a few others, less well know). And my understanding is that it's divalent europium, Eu2+, that emits this blue fluorescence, though there may indeed by other rare-earth elements present that help absorb the UV light that is re-emitted by the europium (and thus, they would be co-activators). But I don't think there exists any hard data as to whether or not there are such co-activators, and just what they are or what their role may be. (There's still a lot of research left to be done to really understand this sort of thing!)

And of course, the only way to synthesize such calcite, would be to precipitate calcite from a solution that contains europium salts (and varying the oxidation state of the europium, Eu2+ or Eu3+, is another variable that one could experiment with), and see if the presence of other REE, or the temperature at which the calcite was deposited, etc., had any effects on the fluorescence. This type of synthesis experiment, unless done under high pressure hydrothermal conditions, would only produce a very fine-grained powdered form of calcite, not macroscopic crystals.

I'm about run out of ideas for a response, after saying this!

[Josele]

While it is true that some information talk about Eu as activator of blue fluorescence in calcite, I can not found any serious paper or reference confirming this assertion. Will appreciate any help to find it.

At the moment, after re-reading all relative to calcite in Luminescence Spectroscopy of Minerals and Materials of M. Gaft et al., must insist in uncertainty of which activator causes blue fluorescence in calcite.
Is well stablished that Eu2+ can activate blue fluorescence in fluorite, apatite, Baryte, danburite, feldspars, anhydrite, zoisite and charoite (page 331, Table 12.1, REE luminescence centers detected in minerals, where calcite is not listed in Eu2+ activated minerals). This does not mean that can't occur, just that the authors they have not found it.
In chapter Unidentified Luminiscence Centers (paragraph 5.11.4 Calcite, page 250), authors say: "Under short-weved UV lamp excitation (254 nm) visually observed luminiscence of calcite is violet-blue with very long phosphorescence time of several seconds. ..." whose characteristics closely resemble to Terlingua-type calcite. After a discussion of tests results they don't arrive to a consistent identification of the activator and concluded "Additional research needed in order to clarify this problem".

In other hand, regardless of activators, I think, as Pete, that must be not easy to crystalize fluorescent calcite with home-made systems. That's why I encourage Parvin to explain his method.

[Pete Modreski]

Josele, I want to retract/amend my statement that europium (Eu2+) is responsible for the blue fluorescence of some calcite. I agree with what you've quoted; there really is no hard evidence for this, it is just a statement that was based on supposition. I shouldn't have been making that claim without checking out the sources (if there even were any!). Thank you for pointing this out.

[Josele]

Thank you, Pete, for relating Parvin's question with Terlingua-type calcite. My knowledge is very limited but I became curious and I was lucky for having the right consulting book.

Let me take this thread to another question about fluorescence. I have understood that each activator emits in a determined range which corresponds to a color, then, what causes white fluorescence? White is the addition of all visible colors together. When we see a white fluorescence, that means there is three or more activators emitting in a range that added to others create white light?
Very strong emission in any color also is seen white, but usually can see the color in the edges of the piece. However sometimes fluorescence is pure white, how does it work?
Comments will be appreciated, thanks for your interest.

[CranCowan]

The most commonly blue fluorescing calcite (under SW) is probably the so called Terlingua-type.

It's activator is thought to be organic. (Robbins, Graft ...)