Workgroup    Fluorescence
Spectra Sulfates - Molybdates - Tungstates
 
Powelliet
This is an intrinsic fluorescence, analog to that of scheelite. It is typical of complex anions with a central metal ion that is surrounded by oxygen ions. The general term for this mechanism is 'charge transfer', in which electron transitions happen between oxygen and the central metal ion. Examples of such anions are: WO42-, MoO42-, VO43-, TiO68-, UO22+, etc... This mechanism invariably involves extremely broad emission bands.
Measured with: Ocean Optics Flame spectrometer, reflection/backscattering probe and a 255 nm LED light source.
Calibrated with Ocean Optics HL-2000-CAL
 
Powelliet - Cu (Cupropowelliet)
The fluorescent color appears, just like the color under ordinary light, somewhat greener than that of pure powellite. The difference is however very small when we compare the spectra. It's a similar effect as when sunlight shines through a green colored glass. A small amount of the red light in the powellite fluorescence is absorbed by the copper. As a result we perceive this fluorescence as a tad greener. However, the fluorescence mostly happens at the surface of the crystals. This renders the path length of light emission through the colored crystals and, as a result the absorption of red light, very small.
Measured with: Ocean Optics Flame spectrometer, reflection/backscattering probe and a 255 nm LED light source.
Calibrated with Ocean Optics HL-2000-CAL
 
Creedite
A strong peak is seen in the region just above 300 nm. Gorbets and Gaft both assign that to trivalent gadolinium. This massive fluorescence in the midrange UV triggers two other activators that appear to be present: Ce3+ and Eu2+. The fluorescence of cerium is seen in the violet and probably in the tailing of the gadolinium peak. Divalent europium causes a broad peak that runs from 380 nm to 450 nm. It thus overlaps with the emission of the humic acids. The comparision of the spectrum with that of a Bolivian specimen demonstrates the importance of the rare earth elements in this blue fluorescence.
 
Caracolite
The very strong emission peak of lead dominates this spectrum of caracolite under short-wave UV. The violet blue fluorescence that we see with the naked eye is but a few percent of the very strong fluorescence which manifests itself in the UV. A weaker emission is visible in the blue-green part of the spectrum. Presumably, it is due to some organic material. That lead can cause a strong fluorescence even in glass is demonstrated in the picture below.
Bohemian crystal "bonbonnière" under halogen and SW-UV light.
Copyright © 2014 by Axel Emmermann  ·  All Rights reserved  ·  E-Mail: fluorescentie@minerant.org
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