UV-Vis Spectroscopy is an optical technique that measures change in UV and visible light intensity upon interaction with matter as a function of the wavelength. UV-Vis spectroscopy mostly probes electron transitions. Typical examples are: transitions from π and n orbitals to anti-bonding π* and σ* orbitals in conjugated organic molecules; d-d transitions in transition metal ions; charge transfer transitions in some organic and transition metal compounds; band gap transitions in semiconductors.
How it works — In a traditional transmittance geometry, a collimated beam of monochromatic light passes through a sample. The intensity I of the transmitted light is measured and compared with the reference intensity I0. A ratio I/I0 as a function of the wavelength is the result of the measurement (UV-Vis spectrum). In many cases the light absorption in a material is proportional to the concentration of absorbing molecules. This phenomenon is formalized in the Bouguer-Lambert-Beer (or Beer-Lambert) law. It is the basis for using UV-Vis spectroscopy for quantitative analysis.
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Instrumentation Available
Key Attributes
- UV wavelength range: 190-400 nm, visible range: 400-700 nm, NIR range: 700-2500 nm. Refer to description of a specific instrument for available wavelength range.
- Typically room temperature measurements.
- Testing of a broad range of materials – solids, liquids, and gases – depending on the accessories available.
- A range of measurement geometries are possible, including transmittance, reflectance, scattering.
Strengths
- Fast sample analysis
- Non-destructive technique
- Relatively small sample size
- Quantitative analysis possible
- Well developed mature technique; a variety of instruments and accessories are commercially available
- Clear physical meaning of the results
Limitations
- No direct information about structure
- Relatively low sensitivity
Applications
- Quantitative analysis
- Kinetics of chemical reactions
- Band gap measurements
Additional Reading
