Red spinel, continuum transmission structure
This is an experiment to look at the transmission spectrum of natural red spinel in the region of the characteristic red 'organ-pipe' fluorescence of this chromium containing allochromatic mineral. In order to minimise the strength of the white light fluorescence, the lamp used for the transmission was filtered with a Schott RG610 red-pass filter.
The continuum transmission structure in the region from 600 to 750nm is of very low amplitude but is clearly detected in this average of high s/n spectra of two natural red spinel samples (orange line). To make the structure more visible, I fitted the transmission continuum continuum with a polynomial (6th order) to flatten it by division. I then subtracted 1 from the ratio, multiplied by an amplification factor (20) and added a constant (60) to shift it up the plot (thin red line).
The thin light blue line shows the polynomial fit and the thin green line shows the 404nm laser excited fluorescence spectrum. The region of the amplified continuum longward of 750nm can be used to judge the noise level of these spectra
The transmission and fluorescence spectral features above 700nm appear to track one another quite closely. Below 700nm however, there are clear wavelength shifts between the absorption and emission structures that are very reminiscent of the Fano (anti-)resonance structures seen in other Cr3+ minerals such as kyanite, emerald and tanzanite.
Red spinel, continuum transmission structure
This is an experiment to look at the transmission spectrum of natural red spinel in the region of the characteristic red 'organ-pipe' fluorescence of this chromium containing allochromatic mineral. In order to minimise the strength of the white light fluorescence, the lamp used for the transmission was filtered with a Schott RG610 red-pass filter.
The continuum transmission structure in the region from 600 to 750nm is of very low amplitude but is clearly detected in this average of high s/n spectra of two natural red spinel samples (orange line). To make the structure more visible, I fitted the transmission continuum continuum with a polynomial (6th order) to flatten it by division. I then subtracted 1 from the ratio, multiplied by an amplification factor (20) and added a constant (60) to shift it up the plot (thin red line).
The thin light blue line shows the polynomial fit and the thin green line shows the 404nm laser excited fluorescence spectrum. The region of the amplified continuum longward of 750nm can be used to judge the noise level of these spectra
The transmission and fluorescence spectral features above 700nm appear to track one another quite closely. Below 700nm however, there are clear wavelength shifts between the absorption and emission structures that are very reminiscent of the Fano (anti-)resonance structures seen in other Cr3+ minerals such as kyanite, emerald and tanzanite.