I have data for reflectance vs wavelength by uv vis nir. I want to calculate R∞ for our sample and after that I want to calculate K-M (Kubelka-Munk) function (f(R∞)).
Well, it is easier to measure it than to calculate - you would just need a layer thick enough that the reflectance would not change, if you further increase the thickness. If you cannot produce such a thick layer, than you need to measure the reflectance for at least two different and known layer thicknesses. With this, you could try to derive the scattering coefficient provided that the absorption coefficient is negligible for the chosen wavelength. If absorption is strong, things get even more complicated. You can find out more for example in the "Phosphor handbook" (eds Yen, Shionoya, Yamamoto). Maybe there is also some useful literature on pigments. Not an easy task, I'd better measure a thick sample.
Apply the following relations as required with the experimental data.
[I] The well known relation is:
R+A+T=1.
Because the sum of Reflectivity (R), Absorbance (A) and
Transmittance (T) is equal to one.
[IIKnowing α (the optical absorption coefficient ), calculate the thickness (t) of the optical material by applying the relation:
α. = 2.303A/t
Or
If thickness of the material is given, calculate A, the absorbance.
Or
Still there is another way to calculate α if band gap of the material is known as:
α = (h. ν -Eg) ^1/2.
[III] Again, knowing α, calculate k; the extinsition coefficient as:
k= α λ/4π .
I[V]T is exp’tlly known.
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