Fluorite fluorescence - new red component

This is the fluorescence spectrum of one of a mass of blue-green fluorite (Ca F_2) crystals. The word 'fluorescence' was coined by George Stokes in 1852 following his observations of this mineral when he realised it emitted light of a longer wavelength than the illuminating source. ("On the Change of Refrangibility of Light", G. G. Stokes, Phil. Trans. R. Soc. Lond. 1852 142, 463-562). [note. actually the coining of the term is in a footnote to a subsequent short paper on an extension to his experimental method: the use of 'crossed filters']

The fluorescence was excited using a defocussed 20 and 500mW 404nm (violet) diode lasers and the spectrum observed with a 350-1000nm Ocean Optics JAZ spectrometer - the input fibre of which is seen in the photograph.

By making two observations, with and without a yellow filter to block the laser light, I was able to build a fluorescence spectrum from 400 to 1000 nm with a dynamic range (range of brightness) of over 4000:1. This is shown as the logarithmic plot. The blue peak at just over 420nm is the well-known divalent Europium fluorescence which was seen by Stokes.

At a much lower intensity, between 550 and 800nm, there are a series of seven or eight spectral ripples similar to the sulphur (S_2^-) bands in sodalite and other sulphur ion containing minerals (hackmanite and delhayelite). In addition, there are narrower lines at 567, 573, 586, 591, 604, 613, 652 and 759nm, presumably arising from the lanthanide rare earths: these are seen in the inset linear plot.

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