Fluorescence Excitation-Emission Spectra of Chromium-Containing Gems: An explanation for the effectiveness of the crossed filter method, Hoover, D.B., F.G.A., and Theisen, A.F., May 1993, The Australian Gemmologist. pp 182-187.
|Shown here are a series of Sweetgum leaf fluorescence
measurements for progressive stages of senescence and chlorophyll loss
or conversion. While these are grossly different and visually obvious,
this spectral method, and the compatible 2-D spectra obtained from the
PolyChromatic, provide a way to sense the subtler transitional changes.
|Another use of laboratory fluorescence collected and displayed as Excitation- Emission-Matrix (EEM) plots is shown here. Oils from different sources are seen to differ spectrally. Even though they are very similar, such as the first three on the left. Two oils from Alabama are seen to be very different, while the Chunchula oil is seen to be very similar to the generic 45 API gravity crude.|
latest Excitation-Emission-Matrix (EEM) data are collected with a Fluorolog-3® Research
Spectrofluorometer (FL-3). This instrument Includes:
o a 450 W ozone free Xenon source and power supply,
o a double Czerny-Turner excitation monochromator with a 1200 g/mm grating blazed at 330 nm,
o a double Czerny-Turner emission monochromator with a 1200 g/mm gratings blazed at 500 nm,
o a multi-alkali Photomultiplier Tube (PMT) emission detector (R928P) with photon counting
electronics and an output range from 190 nm to 860 nm,
o computer controlled, continuously adjustable entrance and exit slits,
o a T-format sampling module with reflective optics and photodiode reference detector,
o a secondary single monochromator with 600 g/mm grating blazed at 1000 nm,
o an extended infrared capability with liquid nitrogen cooled InGaAs solid state detector with an
output range from 1 ìm to 1.5 ìm at 77K (-196 ºC), and
o a fiber optic sample chamber platform with a 2 m, bifurcated, randomized, fiber optic bundle.
FL-3 is autocalibrating, upon initialization, based on a
file. However, the accuracy of this file is checked regularly. Unencumbered
and non destructive fluorescence measurements of samples that do not
fit standard accessories, loose granular materials, powders, or even
liquids require horizontal placement. This configuration is
accomplished through the use of a large external sample chamber and a
bifurcated fiber optic cable.The chamber system was originally
developed for the repetitive measurement of live plants undergoing long
term stress treatments.