Fluorescence Spectroscopy

Fluorescence spectroscopy is a type of electromagnetic spectroscopy. Devices that measure fluorescence are called fluorimeters. Molecules have various energy states. Fluorescence spectroscopy is primarily concerned with electronic and vibrational states. The molecule being examined has one state of low energy and an excited electronic state of higher energy. Within each of these electronic states are various vibrational states. Collisions with other molecules cause the excited molecule to lose vibrational energy until it reaches the lowest vibrational state. Fluorescence spectroscopy analyzes the different frequencies of emitted light and therefore determines the structure of the different vibrational levels.

Measurement theory

A beam of light (usually ultraviolet light coming from lasers, LED, and xenon arcs or mercury-vapor lamps) excites the electrons within the molecules causing them to emit (not always visible) light. A laser only emits light of high irradiance at a wavelength interval under 0.01 nm. A mercury vapor lamp emits light near peak wavelengths. A xenon arc has a continuous emission spectrum in the range from 300-800 nm and a sufficient irradiance for measurements down to just above 200 nm.

The light passes through a filter or monochromator and strikes the sample. Is absorbs the light and the molecules in the sample fluoresce. This fluorescent light passes through a second filter or monochromator and reaches a detector, placed at 90° to the incident light beam to minimize the amount of transmitted or reflected light. The detector then measures the incoming light and its wavelength, characteristic for the specific organic compound.

Benefits
  • Quick respond to concentration changes
  • Analysis of various states of aggregation (liquid or solid, irregularly shaped)
  • Non-destructive to the sample
  • No hazardous by products
  • Well-suited for in-situ studies in the lab and directly on the field
Examples of use
  • Analysis of organic compounds in (bio-)chemical and medical research fields as well as in agriculture and food production
  • Detection of compounds present in air or water, even in very low concentrations
  • Heavy metal detection (e.g. mercury)
  • Redirection of photons
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