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Through my spectroscope July 2010

Crystal of neodymium pentaphosphate

The spectrum of the rare earth element neodymium is seen in several minerals and man made artificial products. Often it may be only partially seen as a weak absorption of the yellow when a small percentage is present, as in apatite. Artificial materials such as pink YAG may resolve the group of fine lines in the yellow but often the lines in the red and blue are less well defined. In some gemstones lines in other areas of the spectrum may be obscured due to strong absorption by the host material. The above biaxial crystal of the man-made laser material neodymium pentaphosphate, kindly on loan from John Koivula, produced three variations of spectra according to the optical direction in which they were viewed. In some directions the groups of lines in the blue, green and yellow could not be resolved as they coalesced to form a broad dark absorption band. All these lines are not visible together in any one direction but to let you see the extent of the truly dramatic spectrum I have linked several images together ensuring that the complete spectrum has been carefully calibrated to give a true representation.

Through my spectroscope April 2010

Try a little magic with your spectroscope

For those with a spectroscope with a built in wavelength scale you may wish to check out it's accuracy and compensate if necessary. Even if it is a more simple instrument you may need a marker to compare the position of absorption lines in a gemstone spectrum. Here I have simply rubbed some household salt into the wick of a candle which, when lit, shows the bright emission lines of the sodium doublet. As you can see candle light consists of mainly red and orange light with weak transmission in the green and almost no blue. For this reason Alexandrite worn by the Russian aristocracy in candlelight would have exhibited such a magical red glow.

Through my spectroscope March 2010

BNX0980. Xenotime crystal from Pakistan

ώ - the ordinary ray vibrating at right angles to the "C" axis

ε- the extraordinary ray vibrating parallel to the "C" axis

As you can see the above somewhat unattractive brown crystal produced one of the most outstanding rare earth spectra I have seen. The material is of interest mainly to the spectra enthusiast or to the mineral collector. This yttrium phosphate often contains small traces of cerium, erbium and thorium which are probably responsible for the striking spectrum. If you can observe it's spectrum do so while rotating a polarising filter and watch certain lines dance from side to side, as each of the two vibration directions come into line, according to the tetragonal symmetry. These spectra are the "Colour signature" of this particular specimen but may be seen to some degree in other samples of Xenotime.

Through my spectroscope Jan. 2010

A colleague of mine described this as "Beautiful" and I then that realised that most spectra are. I was so taken up with the technical aspects of spectroscopy that I had missed the obvious as so often can happen with our work. This is the diffraction type emission spectrum of a triphosphor fluorescent tube commonly called an "Energy saving lamp" Have a look with your spectroscope and enjoy the spectacular view. The brightest line in the orange lies at 611nm. The one in the deep violet at 405nm. has been captured by the digital camera but you may not be able to resolve it by eye. Some of my colleagues say they can see it but I can't - Perhaps it's something to do with age? Have fun while you can!

Through my spectroscope Nov. 2009

Now what do think this one might be?

It's what you might see if you are holding a gemstone in your fingers while you search for a spectrum. Stray light enters your spectroscope which has transmitted through the edge of your skin. Yes it's blood, not just any old blood but my last drop sweated for you in the service of gemmology.