I measure absorption spectrum using UV-Vis NIR and excitation spectrum using fluorescence spectroscopy for ruby crystal. Absorption spectrum shows the most absorb wavelength while excitation spectrum shows the best wavelength to pump the crystal. Should it be the same?
It is depend on the useful techniques and samples . As I know that there are 2 techniques for measuring the excitation and the absorption spectrum. the first is the absorption spectroscopy technique which is a standard technique always give a bad signal-to noise ratio and the second one is the technique that you use for your measurement " the fluerescense spectroscopy technique" which is a sensitive method for measuring the absorption profiles if the quantum yield of "the radiative decay" is very high and if the useful sample is with a high degree of condensation such as solid or crystal (which is the case in your experiment) or very intense beam of large cluster. In this case light emitted from the excited sample is taken as a monitor for the absorption and the measured fluerescence excitation spectrum is equivalent to an absorption spectrum. However this is not always correct especially if the sample is optically thin cause in this case the "nonradiative decay channels"
are of major importance and then the quantum yield of the radiative decay is very low. Here you have to distinguish the meaning of the excitation and absorption spectrum and take separately their measurements.
The difference is, that for an excitation spectrum you measure fluorescence (while changing the excitation wavelength) and for absorption spectroscopy not, there you measure, how much incoming light is absorbed.. If there is an absorbing species, that you can measure via absorption spectroscopy that does not fluoresce, there are differences in absorption and excitation spectra.
One example is H-dimerization of organic dyes: In high concentrated sample MR121 builds complexes that absorb blue shifted to the monomeric MR121. Both species exist in the high concentrated sample. Therefore you can see in the absorption peaks at 660 nm and 608 nm in water. Excitation spectra only show the 660 nm peak, because the complexes do not fluoresce.
There ishas been a very long thread in the topic Fluorescence, see there for a general discussion
What's the difference between an excitation spectrum and an absorption spectrum for the same molecule?
in topic
Fluorescence Spectroscopy; Spectroscopy
see there
Hello Dear,
Following link might help you.
https://www.olympus-lifescience.com/zh/microscope-resource/primer/lightandcolor/fluoroexcitation/
Best,
Shravan B Rathod
Absorption spectroscopy and excitation spectroscopy (through measurement of fluorescence) provides nearly similar spectrum. The technique of recording the spectra are different. However there may be some case that some molecule absorbs but don't provide fluorescence in that case spectrum may vary. This is the case when molecules de-excite through non-radiative transition.
Again
there are very extensive answers here:
" What's the difference between an excitation spectrum and an absorption spectrum for the same molecule?"
in the topic "Fluorescence"
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