What is Fluorescence Spectroscopy and Why is it Important?
Light interacts with matter in a few basic ways: reflectance, transmission, and absorption. In some cases when light is absorbed it will be re-emitted as light at a longer wavelength. The most obvious example of this is ultraviolet fluorescence. The sample absorbs UV light (invisible to the human eye) and emits light in the visible region. This causes the sample to have a unique color only when observed under UV light. Measuring this reaction using spectroscopy gives insight into a sample’s composition.
Fluorescence spectroscopy is commonly used across the sciences for a variety of purposes. This technique enables researchers to quantify or identify materials using low cost and portable instruments called fluorimeters. This method is also non-destructive and does not require extensive sample preparation. The benefits of fluorescence spectroscopy make it ideal for biological, chemical, and environmental applications.
Fluorescence Spectra of Fluorite (blue), Wernerite (yellow), Calcite (pink), & Tremolite (orange) using a StellarNet preconfigured Fluorescence System
Fluorescence spectroscopy is vital to geology, gemology, and mineralogy. It can be used to characterize fluorescent minerals in the field and authenticate different materials. For example: natural rubies, emeralds and diamonds fluoresce in the red region when long wave UV light is absorbed. This method can be implemented to rapidly identify counterfeit gems.
The type of fluorescence of a sample can also indicate its makeup and detect impurities. Sphalerite is a mineral made up of many elements. The ratio of the common elements like magnesium, Zinc, and others determine whether its fluorescence is a pale yellow, or a bright orange. Using a calibrated fluorimeter is an easy analytical method for accurately determining sample composition.
Here are some examples of fluorescent minerals and their fluorescent emission color responses when excited by long and short wave UV light:
Fluorescent Minerals |
||
| Mineral | Short Wave | Long Wave |
| Hackmanite | Pink | Orange |
| Wernerite | Dark Yellow | Dark Yellow |
| Opalite | Light Green | Light Yellow |
| IcelandSpar (Calcite) | White – Pink phosphorescent | Cream –Pink |
| Chalcedony | Bright Green | Yellow- Green |
| Albite | Dull red | Dull pink |
| Sheelite in Tungsten ore | White | — |
| Willemite | Orange-red | — |
| Tremolite | Orange | Pink |
| Fluorite | — | Blue-Purple |
| Turritella Agate | Cream-Yello | Cream-Yellow |
| Fossil Algae | Cream-Orange | Cream-Yellow |
| Scapolite | Deep red | — |
| Calcite | White- Pink Phosphorescent | Cream-Pink |
| Resinous Coal | Yellow-White | Yellow-White |
Compact spectrometer systems preconfigured for fluorescence may consist of an LED excitation source with various UV wavelengths, a fluorescence probe, and a high sensitivity TE cooled compact spectrometer such as the BLACK-Comet-TEC or SILVER-Nova models. These spectrometers are designed to analyze a wide range of fluorescent signals from the UV into the NIR. Samples with weak fluorescent response are eahttp://BLACK-Cometsily detectable with the instrument’s high sensitivity and large dynamic range.
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Application Note- Fluorescence Spectroscopy of Rocks and Minerals
