I have been working on ternary and quaternary Cu based chalcogenide nanocrystals. I have measured the UV-vis-NIR absorption spectrum to calculate the band gap. From literature I came to know that the well known method to calculate the band gap is to use the (αhν)2vs hν graph. Where "α" is the absorption coefficient.
How to calculate the absorption coefficient of colloidal nanocrystals from absorption spectra?
You should not be deceived by seemingly simple way of producing results from your experimental data. The coefficient of absorption of the bulk material (which is implied in the calculation method you describe above) and the coefficient of absorption of colloidal dispersion ain't the same thing. You can read more on that in my review on luminecsent nanoparticles, Sections 4.1 and 4.2:
https://www.researchgate.net/publication/259717755_Nanophosphor_Coatings_Technology_and_Applications_Opportunities_and_Challenges
I suggest that the best way to find the bandgap of your nanoparticles would be to produce a continuous dry film (or at least smooth highly concentrated wet film) and give it a Kubelka-Munk (google "KM theory") treatment (if the film is strongly scattering). If you obtain a transparent (that is, non-scattering) coating, you probably could substantially simplify the calculation by using the effective medium approach. You should determine the complex refractive index of your film and particle volume fraction in it. Using them (and assuming you know the refractive index of the solvent, if the film is wet) you can calculate the "bulk" refractive index of your particles (for example, by Yoldas mixiung rule) and then treat it the way you initially wanted.
Article Nanophosphor Coatings: Technology and Applications, Opportun...
The light absorbance coefficient , and films absorption coefficient are given by the equation:
αop=2.303A/d
Where (d) represent a thickness of film in the case the prepared material as a film but in collide can use the distance of propagation wave from the dimensions of collide billy runway.
In general to plot the Tauc Plot ((αhν)2vs hν) you can use the Y-axis values (from absorption spectrum) as α values in (αhν)2 calcualtion.
Dear Mr. Parthiban Ramasamy ,
we have only some ideas for a absorption coefficient in the radar range. You must use the mie absorption radar effect. It is to use the surface area , the frequency, the material bulk conductivity and so on.
The difference between the absorption coefficient of a nanoparticle and a bulk particle is the surface area effect.
All the best
F. Gräbner
The absorption coefficient α is expressed from the Beer-Lambert law
α =2.303A/d
Where A is known as the absorbance, d is the thickness
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