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Calcite, two step actiavtion of Mn via Ce

Calcite skalenohedron, Beez, Namur, Belgium. This a special crystal. Instead of the usual organic yellow fluorescence, it shows an orange Mn2+ fluorescence under 365 nm excitation (black solid line). The orange fluorescence is enhanced via a two step mechanism, in this case Ce3+ (instead of Pb2+). We can see this clearly at 275 nm excitation. The intense purple fluorescence is caused by Ce3+ (black dashed line). It is this Ce that transfers its energy from the excited level to the Mn2+, intensifying that fluorescence. Excitation at 255 nm shows a more yellowish colour, caused by the simltaneous presence of multiple bands (grey dotted line).

The crystal is also interesting because it shows a twin line, but it is not a twin. On the visual foto you can see than an oblique angle at the top part has an obtuse counter part in the lower part. This is typical for a single crystal skalenohedron. We assume there is an (invisible) microtwin in the centers that annihilates the twinning effect in the major parts.



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