Dear Yulia, I don't know how to calculate R(hv) value. I have % reflectance and wavelenght, if you see my attachment I have attached you can understand. From this % Reflectance value, how can I get R(hv) value. Please tell me.

You can use the Kubelka-Munk equation for this.

It is used to convert DRS data into "absorption data". Then you can simply plot the converted data and you will see the strong absorption band correlating with the optical band gap.

Beware though - optical band gap and electrical band gap may / will differ!

Thanks for your concern! Could you give me a ference or a web link? Some works reported that the optical band gap can be obtained by drawing two lines in the diffuse reflection spectrum. The crossing point shows the location of the optical band gap, as shown in the blow picture. Is it right?

You might want to check this PDF file here:

http://www.piketech.com/files/pdfs/DiffuseAN611.pdf

It gives you a brief description of the equation and the respective parameters.

The major question is - what did you measure? Usually for a bulk material you can't just measure the absorption, therefore one measures the reflection which then can be converted into what is equivalent to an absorption spectra.

From there you can obtain the band gap as given in your graph, although in my work we have determined the band gap as shown in this graph:

http://www.azom.com/work/U2PRC2H9a2KSYhny8h67_files/image007.gif

I hope this helps!

Thanks for your help! However, I do not know how to get 2.57eV for my graph. What should I deal with S, K and R? Would you like to give me an explaination process as a word form?

The main question is - what did you measure?

Without a detailed knowledge of how the data you gathered looks like it is very hard to give you any further advise.

If you can sent me an image of your data or the data itself I could help you by applying the Kubelka-Munk equation on your data.

Here is what you do in words - maybe this helps in addition.

If you have a reflectance measurement as intensity versus the wavelenght you first convert the wavelength into energy in eV (1240/lambda).

Second you calculate k by dividing the intensity (100%) by 100 and then doing ^2. k = (Intensity / 100)^2

f = intensity / 100

Finally it's just k / f which gets plotted versus the respective energy in eV.

I hope this helps!

Thanks for your help! I measured the diffuse reflection spectrum of our sample. The data is attached. The abscissa is wavelength (nm), and the ordinate is diffuse reflectance (%). Please help us by applying the Kubelka-Munk equation.

Dear Xiangfu,

find attached the applied Kubelka-Munk equation.

From my interpretation the band gap of your material is ~2 eV. This should correspond to a red color of the compound.

Please consider this carefully! Since I have no idea if you calibrated the instrument on 0% and 100% reflection I can't give you any help on how precise the interpretation I made is.

In the data sheet you can find the mathematical step how I applied the Kubelka-Munk equation.

Thanks for your help.

 Oliver, 

Do you have any document for color vs band gap value?

Oliver, when you calculate using Kubelka-Munk equation, what's the mean of f, why it can not using f(R)=(1-R)^2/2R directly?

Thank you

Dear Oliver,

You had taken the intersection of tangents as a point for determining Eg(band gap). But some literature suggests that intersection of y=0 (zero absorbance) and tangent at inflection point would give Eg value.

Please help me to clarify the ambiguity.

Thank you

hi

thanks alot

i hope a clear future for u

Hi

I have the same question that  Mr Abhishek Agarwal has, please  can anyone help us?

thank you

We are studying solids. UV-visible measurements are performed with a Diffuse Reflectance cell and it is then a reflexion of light that is measured.

Using the Kubelka Munk expression is an approximation to convert the measured signal in something equivalent to absorption, as measured with solutions.

I have in mind that the conversion was made using: (1-R^2)/2R and the mathematical expression given in your document is different (1-R)^2/2R. Do you know which expression is correct? I will check

but for me, i got negative value. what can i do for that. is there any remedy? pls explain 

Dear all.

May be, these articles will help you.

The spectral dependence of reflectivity can be directly converted to one for absorption coefficient and then using the Tauc equation the band gap can be determined, as it is discussed in the attached publications.

This link may help,

http://www.instanano.com/characterization/theoretical/uv-vis-spectroscopy-band-gap-calculation/

Thank you.

Hi please tell me how to calculate band gap by using Kubelka munk function. Here I am attaching my data. How to plot graph between F(R) hv versus hv. What values I need take for plotting. Please explain.

Dear Sangeetha,

If you have the reflectance data R(hv), it is possible to calculate the Kubelka-Munk function using following equation:

F(hv)=(1-R(hv))^2/(2R(hv))

And then you can plot F(hv) versus hv. The Kubelka-Munk function is proportional to absorption coefficient, so one can use the Tauc equation:

(F(hv)*hv)=A*(hv-Eg)^n, where steepness "n" depends on type of electron interband tranitions (direct or indirect, allowed or forbidden). If the linear region in plot (F(hv)*hv)^(1/n) versus hv will be determined, you can obtaine the value of band gap by approximation this linear region up to the abscissa axis.

Dear Yulia, I don't know how to calculate R(hv) value. I have % reflectance and wavelenght, if you see my attachment I have attached you can understand. From this % Reflectance value, how can I get R(hv) value. Please tell me.

Dear Sangeetha, here I attached the file with Kubelka-Munk's function (second column) that depends on photon energy (first column). The wavelength values in your data I convert to energy as Energy=1240/Wavelength. Then the % reflectance was converted to absolute values by divided on 100%. And then I use following equation:

F(hv)=(1-R(hv))^2/(2*R(hv)) for determine the F(hv)-Kubelka-Munk function. So in attached file F(hv) dependence is presented.

 Hi Yulia, How to calculate (F(R))hv)2 from the reflectance

I recommend the book "Photoelectrochemical Water Splitting Standards, Experimental Methods, and Protocols" by Zhebo Chen, Huyen N. Dinh

& Eric Miller for of UV Visible characterization and band gap analysis. its a very good read.

@ Yulia Kuznetsova I need your help please

It's very interesting. Thank you so much.@

Dear Yulia Kuznetsova Thank you so much ,I have enough understanding for defuse reflectance data.