For some time I've been investigating the fluorescence spectra of various minerals using a 405nm laser diode pointer. These devices are available from China at very reasonable prices, and produce a very nice monochromatic line with a width of less than 20 nm. The brightness of these lasers causes a very nice response in many minerals that do not show normal fluorescence in short, medium or long-wave UV. Minerals that do fluoresce in LW UV tend to give an overwhelmingly bright response.

Data for this study were collected using an Ocean Optics HR2000 spectrometer that has been upgraded to the equivalent of an HR4000 ES. Typical integration times ranged from 200 milliseconds to 4 seconds for very weak fluorescence. The spectra were captured using OO's Sectra Suite software. The spectra were saved as .jdx files and processed using SpecWin32 software. SpecWin32 allows stacking of spectra and output as .bmp files which can be coverted to .jpeg files for use in Mindat. Neither program allows direct annotation of the output. SpecWin32 will output a separate file listing the spectral peaks.

Collection of the data was quite easy. I constructed a holder for the HR2000 collimator feeding the fiber optic connector. The sample was placed about 1 cm from the collimator and illuminated with the laser. Adjustment of the integration time was used to bring the spectrum into the normal graph limits pre-set into Spectra Suite. A one-shot capture was used to collect the spectrum. This set up was found to work with everything from 3mm micromounts to large (7cm+) specimens. A laser with a lockable on-off switch would make the data collection a lot easier. I'm working on that one.

Here are some examples of spectra I've collected (the strong peaks at 405nm and 810nm are first and second order lines from the laser).

Fluorapatite from several locations showing strong REE lines and broadband emission. Interestingly, the strongesst SW fluorescence was in the specimen with the broadband emission.



Here is a comparison of REE lines in a sample of scheelite from China and an interesting fluorapatite from Yukon, Canada. Both samples glow a pink color when illuminated by the laser. The REE lines are essentially identical in both samples, which argues that little shifting of REE lines occurs between mineral species.




Here is a comparison of two specimens of spodumene from Minas Gerias, Brazil. One is pink kunzite variety, the other green hiddenite variety. They demonstrate rather different spectra. The most unusual thing is the distinct Cr line in the hiddenite. Chromium is an element, like rare-earths, that is strongly stimulated by the 405nm laser.



Here is an example of Cr lines in two specimens of kyanite, a blue-green sample from Brazil and a orange sample from Tanzania. Tests of other blue and green kyanites show identical lines.



Here is an example of several other fluorescent minerals under 405nm laser illumination. The two calcites are from Naica, Mexico and the Wessels Mine in South Africa. Both luminesce a deep red using the laser. The adamite is from Mapimi, Mexico and fluoresces a blindingly bright green color using the laser. The fluorite a a yellow sample collected from Bedford, Indiana that fluoresces a strong blue white in both SW UV and with the 405nm laser



I hope these examples will demonstrate the power of such lasers. I'm awaiting development of inexpensive devices in still shorter wavelengths!