How can excitonic peaks be measured through uv-vis absorption spectroscopy?
It is understood that when light energy above bandgap is applied to a material, an electron-hole pair is generated, and exciton is generated as the electron-hole pair is bound by coulombic interaction. In this case, shouldn't the excitonic peak not appear in the absorbance? Because absorption requires only the energy for which the electron-hole pair will be made and then exciton will be generated by each other's coulombic force (i.e. exciton binding energy).
I'm confused, so please help me.
Dear Yongjin Kim ,
Although absorption and excitation spectra look (in general) quite similar they are fundamentally different terms, see for a pretty good explanation here: https://www.differencebetween.com/difference-between-excitation-and-vs-absorption/
See also https://www.edinst.com/blog/what-are-absorption-excitation-and-emission-spectra/
So, in ‘mechanistic terms’ different the absorption and excitation spectra show high resemblance in most cases, but there are examples where they differ (somewhat):
On, C., Tanyi, E. K., Harrison, E., & Noginov, M. A. (2017). Effect of molecular concentration on spectroscopic properties of poly (methyl methacrylate) thin films doped with rhodamine 6G dye. Optical Materials Express, 7(12), 4286-4295.
So, back to your question: you can get a pretty good idea about the excitation spectrum but strictly speaking you can only obtain an excitation spectrum by using fluorescence spectroscopy.
Best regards.
it would be best if you combined some spectroscopy instruments such as UV-Vis with solid proof and photolumenscence to examine electronic transition and ESR to know electrons with triplet states.
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