Good evening everybody,
at present we are working on a sample of fluorine from the French Alps which displays two interesting phenomena:
(1) Initially colorless and transparent, the samples turn blueish (being still transparent) upon exposure to daylight.
(2) Upon exposure to UV-light (365 nm ) the samples display a bright red-rose fluorescence. No fluorescence at all is observed at shorter wavelengths.
I have read through most relevant literature, but could not find any example for above behaviour.
Any hints/suggestions are welcome !
Thanks in anticipation.
Harald
Good question Harald!
The colour and fluorescence (the term for this phenomenon descended from the mineral name fluorite) of fluorite is still under discussion.
Frequently impurities (rare earth ions) are made responsible.
Another explanation is photochemical reduction of Ca2+ to Ca (sometime referred as "metallic Ca" - which is nonsense a single atom cannot be a metal). I also doubt this and would discuss this reaction in terms of a reduction from Ca2+ to Ca+. However, the electron must come from F- which is the worst electron donating ion you can think of. Thus, irradiation with daylight should not lead to the observed colouration. Also no photochemistry is reported for pure CaF2 crystals (see e.g. http://www.diss.fu-berlin.de/diss/servlets/MCRFileNodeServlet/FUDISS_derivate_000000000200/;jsessionid=8092C8227C69F1423857B4FC8D4C932D?hosts=).
Therefore you should check for other metals as impurities (transition metals) by high-resolution elemental analysis, EDX or PEEM. At the same time you can check if temperature has an impact on the describe phenomena.
Best
:-) Sure, I can try. I have got an X-band Bruker with HQ cavity which means I can detect maybe up to conc. of 10-9 or 10-12 mol of spin-carrying species. If light-irradiation enhances the number of spins ...
Maybe this could also be an application for neutron activation analysis. For the most rare earth elements, the detection limits would be in a similar range of 10-12 to 10-9 mol for a sample of approximately 1g.
Dear all,
first of all THANK YOU VERY MUCH for the feed-back and answers !
As I have been travelling, somehow your replies were transferred to a private e-mail account (mystery of a digital world) which I consult occasionally only .
As to the question of the presence of impurities, there are analytical data: a semi-quantitative ICP-MS-OES-AAS analysis performed by Mikroanalytisches Labor Pascher gave an REE content of less than 0.1 ppm for all forteen REelements ! There seems to be no transition metals or actinides above the detection limit (except Cu, Th; 1 ppm each).
The samples contain Sr (500 ppm) and S (300 ppm), though.
Obviously, the Th-content is sufficient most likely to induce lattice defects on a geological time-scale ... one might speculate in this direction.
Usually, irradiation-induced defects disappear at daylight (or upon heating) - in the present case the inverse behaviour is observed.
Axel, if you could actually record an ESRF spectrum, I would happily accept your proposition.
Thanks again !
Best wishes
Harald
Harald, sure I can do this. Just send me a sample. I would like to test also the effec of crystyl size. So I need one crystal of approx. dimensions of max. 2 mm in width (for a quarz tube) and additional material which I can grind (ball-mill) to microcrystalline powder.
You can send it to: Prof. Dr. Axel Klein, Universität zu Köln, Department für Chemie, Institut für Anorganische Chemie, Greinstrasse 6, D-50939 Köln.
- Badges
- Science method