Hi everyone,
I am reading an article which has measured "extinction spectra" for a dispersion of MoS2, but hasn't explained the details. I wish to measure the same spectrum for a dispersion of graphene flakes obtained by aid of a surfactant. Actually, I don't know much about the difference between "extinction spectra" and "absorption spectra".
I would be deeply appreciated if someone could explain the concepts and the applicable way to measure an extinction spectra.
For definitions check https://goldbook.iupac.org/
extinction This term, sometimes used as equivalent to absorbance, is no longer recommended. (https://goldbook.iupac.org/html/E/E02293.html)
absorption spectrum The wavelength dependence of the absorption cross-section (or absorption coefficient); usually represented as a plot of absorption cross-section versus wavelength of the light (https://goldbook.iupac.org/html/A/A00043.html)
Sea also for "extinction coefficient", "attenuation coefficient," "molar absorption coefficient"
Read textbooks for "the concepts and the applicable way to measure an extinction spectra. "
extinction coefficient attenuation coefficient
Analogous to absorption coefficient but taking into account also the effects due to scattering and luminescence. It was formerly called extinction coefficient.
For definitions check https://goldbook.iupac.org/
extinction This term, sometimes used as equivalent to absorbance, is no longer recommended. (https://goldbook.iupac.org/html/E/E02293.html)
absorption spectrum The wavelength dependence of the absorption cross-section (or absorption coefficient); usually represented as a plot of absorption cross-section versus wavelength of the light (https://goldbook.iupac.org/html/A/A00043.html)
Sea also for "extinction coefficient", "attenuation coefficient," "molar absorption coefficient"
Read textbooks for "the concepts and the applicable way to measure an extinction spectra. "
extinction coefficient attenuation coefficient
Analogous to absorption coefficient but taking into account also the effects due to scattering and luminescence. It was formerly called extinction coefficient.
Actually, if you use a conventional FT-IR or UV-Vis spectrometer, you never measure absorption! What is usually meant with absorption or extinction spectrum is that you measure the transmittance T and convert it to absorbance A by A = -log T, which is in many cases a very bad approximation (see e.g. Article Employing Theories Far beyond Their Limits-The Case of the (...
). Absorbance is nevertheless used, because it seems to be linearly proportional to the concentration. In fact in many instances this is the case, but not in general:Article Beer's Law – Why Absorbance Depends (Almost) Linearly on Concentration
Preprint Beer's law derived from Electromagnetic Theory
If you have a sample that is highly absorbing in the spectral range of interest, I would go for absorptance A instead, which is defined as 1-R-T, so it could be that you have to carry out two measurements instead. Furthermore, you have to apply a wave optics-based evaluation scheme. You can read about this in https://www.researchgate.net/project/Book-Project-Wave-Optics-in-Infrared-Spectroscopy (not yet complete, but the missing parts will be added in the course of next year).
An extinction spectrum is equivalent to an absorbance spectrum. If you want to study the photochemical properties of graphene, you will have to either study its spectroscopic properties in the solid state or in solution state. UV-Visible absorbance and fluorescence spectroscopy will give you data on the ground --> excited state and excited --> ground state transition energies. IR spectroscopy will provide information on the different types of functional groups present in the compounds.
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