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Scheelite, Pingwu, China fluorescence | by The^Bob
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Scheelite, Pingwu, China fluorescence

This shows the fluorescence spectra of a sample of Chinese scheelite excited by three lasers and two Hg discharge lamps covering from 254 to 633nm. The HeNe spectrum (grey line) is shown since it contaminates the 633nm laser spectrum. Regions containing strong Hg emission lines have been removed. The intensity scales are different and have been adjusted for display.

 

The green (300mw) laser measurement used a BG38 filter before the sample to remove the pumping wavelength and an orange filter in front of the spectrometer input to remove the scattered laser line.

 

In addition to the strong, broad blue fluorescence under 254nm excitation, due to [WO_4]^2-, the trivalent rare earth emissions from Dy, Sm, Nd and, possibly, Eu, Tb and Pr can be seen. I have made these identifications using the spectra plotted in the book by Gorobets and Rogojine (2002) "Luminescent Spectra of Minerals", particularly their measurements of synthetic CaWO_4 doped with individual lanthanides. [Note that the marked wavelength scales in the G&R book plots can be in error by more than 10nm: my JAZ wavelength scale has an error of less that 0.5nm.]

 

Looking at the 404nm excited spectrum (green line), the four complex emission bands between 550 and 720nm are predominantly due to Sm^3+ but with components from Eu^3+ at 524, 589 and 702nm. The weak doublet at 479, 488nm is due to Dy^3+. This, and the feature at 575nm (also Dy^3+?) is strong in the 254nm excited spectrum. The emission seen between 543 and 550nm in the 254nm and weakly in the 365nm excited spectra may be due to Tb^3+.

 

Most of the lines at longer wavelengths are due to Nd^3+ although the significabnt emission at about 933nm does not appear in my own spectra of Nd YAG (see: www.flickr.com/photos/bob_81667/6045754362/lightbox/ ). I have not yet been able to identify the emission band between 800 and 820nm seen in the 532 and 633nm excited spectra but this may also be due to Nd. The strong triplet emission between 910 and 920nm does not appear in my Nd YAG spectra.

 

It is possible that the Pr^3+ lines at 605 and 650nm are lurking amongst the Sm lines but I can't be sure.

 

[Replaced by version with new flux calibration (#5) on 28 Sep 2012]

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Taken on September 28, 2012