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405nm laser pointer mineral spectra

Last Updated: 2nd Apr 2011

By Henry Barwood

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!




Article has been viewed at least 14455 times.

Comments

Henry,
Thanks so much for sharing this. The 405nm laser just went higher on my wish list.
Have you thought about looking at the temperature effect on the fluorescence spectra? Perhaps you have access to a thermos of liquid nitrogen from work. Also, how about relative polarization of the fluorescence relative to the laser polarization? For that matter directional spectra from anisotropic fluorescent crystals.
-Dean Allum

Dean Allum
7th Apr 2011 3:48am
Hi Dean,
I'm working on a number of things, but just don't have the time to pursue them all. I have been curious about polarization and may set up to test for it. The lasers are surprisingly useful for all sorts of studies, but my main objective is CL spectroscopy. OO has suggeested that I make a cell with a fixed 90 degree illumination/observation angle and I may set up for that.
Henry

Henry Barwood
7th Apr 2011 12:38pm
Quite impressive, Dean! Thanks for sharing this with us...
I have been working with cathodoluminescence and I found it really impressive!
Can you post a couple of pictures with the settings of your device?perhaps the size of the sample or something for scale would be helpful...

Chris

Chris Mavris
8th Apr 2011 6:19pm
Hi Chris,

I'm using an ELM-2 Luminoscope made by Nuclide. I've actually got three of them, but only use the one regularly. The design has not really changed much since the 1970's and more modern configurations are still available from Don Marshall. I can accomodate everything from sand sized grains to large thin sections or rock slices (2X3 inches). Settings depend on what I'm examining. I like to work at a minimum 12KV and .6 MA, but often push it up to around 16KV. I have a sapphire window so that I can do spectroscopy into the UV, but only put it in when I'm doing spectroscopy to keep X-rays down.

I'm preparing samples for CL spectroscopy, but this time of the years is crazy with tests and advising and registration, so it is taking a fairly long time to get everything ready for examination. I plan on ordering some UV LED's to continue with the fluorescence research, but that will have to wait until May.

Henry

Henry Barwood
8th Apr 2011 9:57pm
Hi Henry,

very nice work!!! It is great that intense lasers are now available at low costs.

405 nm is the strongest absorption band for Sm3+, and the fluorapatites and scheelite clearly shows the typical Sm3+ emissions. I agree that the REE emissions do not move around as much as those originating from transition metals, but your comparison between fluorapatite and scheelite also illustrates that the REE emissions are influenced by the coordination, i.e. site symmetry of the site the occupy. This is something that we often forget/ignore in mineral luminescence.

Looking very much forward to your next articles here.

cheers

Henrik

Henrik Friis
10th Apr 2011 11:57pm
Thanks Henrik,

This is the end of the term here at Troy and in my online classes. That means I have to prepare and grade finals from 9 classes that I teach. That tends to cut into my research time, but it also pays the bills!

While I have conducted emission and absorbtion spectroscopy for many years (along with XRF spectroscopy), this is my first foray into fluorescence. I'm also looking forward to my cathodoluminescence work as soon as my teaching load dies down. In the meantime, I'm trying to prepare samples for analysis. I'm also studying the literature (notably Russian) on spectroscopic examination of minerals.

I had a lot of fun with the laser at Tucson (and annoyed a lot of dealers and exhibitors!). My hope is that they come out with true UV diodes before too long.

Henry

Henry Barwood
11th Apr 2011 4:21am
Hi Henry,

I used some 300 nm and just before I finished my PhD I think we got some 250 or 260 nm diodes. Not cheap but that is already some years back. I used them to try and convert our PL (using a Xe-lamp) into an instrument that would do time-resolved with different wavelengths. Although old (but upgraded) our PL did some excellent luminescence excitation and emission spectroscopy.

I went to my first Tucson this year, so a shame I didn't see you. Your idea with name tags would have been good there.

henrik

Henrik Friis
11th Apr 2011 6:22am
Hi Henrik,

I hope to order diodes in 250, 310 and 340 nm soon. The prices for single units have dropped under $200 now. Of course, if you want to order a million of them, the price gets very reasonable! I tried to retrofit a UV spectrometer to use the UV monochromator, but the intensity output was disappointing. I haven't entirely given up on it, but have only faint hope of making a useable instrument out of it.

Tucson is a fascinating experience. Sorry I missed you, and, yes, nametags would have helped with "distance recognition".

Henry

Henry Barwood
12th Apr 2011 8:35pm
Impressive, Henry!
Many thanks for your infos. It could be quite a handy tool to consider!

Chris

Chris Mavris
14th Apr 2011 2:41pm

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