What is the Difference Between UV Vis and Fluorescence Spectroscopy

The key difference between UV vis and fluorescence spectroscopy is that UV-visible spectroscopy measures the absorption of light in the UV-visible range, whereas fluorescence spectroscopy measures the light emitted by a sample in the fluorescence range after absorbing light at high energy than the emitted energy level.

Spectroscopy is a technique for the measurement of the absorption and emission of light and other radiation by matter.

CONTENTS

1. Overview and Key Difference
2. What is UV Vis Spectroscopy
3. What is Fluorescence Spectroscopy
4. UV Vis vs Fluorescence Spectroscopy in Tabular Form
5. Summary – UV Vis vs Fluorescence Spectroscopy 

What is UV Vis Spectroscopy?

UV visible spectroscopy is an analytical technique that uses the absorption or reflectance of a part of the UV range and complete adjacent visible regions of the electromagnetic spectrum. This technique comes in two types; they are absorption spectroscopy and reflectance spectroscopy. It uses light in the visible and adjacent ranges.

Generally, the absorption or reflectance of the visible range of light can directly affect the perceived colour of the chemicals that are involved in the process. At this range of the spectrum, we can observe that atoms and molecules can undergo electronic transitions. Here, absorption spectroscopy is complementary to fluorescence spectroscopy, where fluorescence deals with the transitions of electrons from the excited state to the ground state. In addition, absorption measures the transitions from the ground state to the excited state.

This spectroscopic technique is useful in analyzing different samples quantitatively, such as transition metals ions, highly conjugated organic compounds, and macromolecules in biological systems. Generally, spectroscopic analysis is carried out using solutions, but we can also use solids and gases.

What is Fluorescence Spectroscopy?

Fluorescence spectroscopy is a type of electromagnetic spectroscopy that is useful in analyzing fluorescence from a sample. This technique involves the use of a beam of light (such as UV) to excite electrons in molecules of some compounds, and it can cause them to emit light. Typically, this emission is visible light but not necessarily the same.

Typically, molecules have different states that are known as energy levels. This technique is primarily concerned with electronic and vibrational states. Often, the analyte sample has molecules in a ground electronic state and an excited state of higher energy. These two electronic states have various vibrational states between them. During the process of fluorescence, the chemical species are excited by absorbing photons and move from a ground state to a higher energy level. Thereafter, the collisions between other molecules cause the excited molecules to lose vibrational energy until it comes to a low vibrational state from this excited state. This emits photons with different energies and different frequencies. This is called fluorescence. We can analyze these different frequencies emitted in this manner to determine the different vibrational levels.

What is the Difference Between UV Vis and Fluorescence Spectroscopy?

Spectroscopic techniques are useful in studying the properties of different chemical substances. The key difference between UV vis and fluorescence spectroscopy is that UV-visible spectroscopy measures the absorption of light in the UV-visible range, whereas fluorescence spectroscopy measures the light emitted by a sample in the fluorescence range after absorbing light at high energy than the emitted energy level. Moreover, fluorescence spectroscopy is more sensitive than UV-visible spectroscopy.

The below infographic presents the differences between UV vis and fluorescence spectroscopy in tabular form for side-by-side comparison.

Summary – UV Vis vs Fluorescence Spectroscopy

Spectroscopy is an important analytical technique. There are different types of spectroscopies, such as IR spectroscopy, UV visible spectroscopy, fluorescence spectroscopy, etc. The key difference between UV vis and fluorescence spectroscopy is that UV-visible spectroscopy measures the absorption of light in the UV-visible range, whereas fluorescence spectroscopy measures the light emitted by a sample in the fluorescence range after absorbing light at high energy than the emitted energy level.

Reference:

1. “Fluorescence Spectroscopy.” UCI Department of Chemistry.

Image Courtesy:

1. “UV-vis” By Jaeger5432 – Self-published by Jaeger5432 (CC BY-SA 3.0) via Commons Wikimedia
2. “PSA 2” By Karelj – Own work (Public Domain) via Commons Wikimedia