I have data of reflecatnce and transmittance. Direct band gap energy can be calculated by plotting Photon energy (hv) versus square of absorption coefficient*photon energy and then drawing a tangent line on the linear portion towards energy axis.
But sometimes its is difficult to guess the transition edge in the plot, please suggest any other method to accurately find the band gap energy.
There is another standard method to find out the band gap from reflection data alone but the errors in taking relectance data may lead to errors in band gap calculations. Reflectance data can have errors due to multiple reflection from mirrors and you have to normalize it before using for band gap calculations.
Modulation spectroscopy (e.g., Photo-reflectance or electro-refletance) measures changes in reflectivity can provide much sharper transitions at critical points such as band gap energies. This is because modulation spectroscopy generate spectra that are change of R divided by R which is similar to taking the derivative of a function, rather than the function itself, this generating much sharper spectra.
Hai,
First convert the transmission into absorbance data simply 1 by t -value equal to abs value. then, You have to find out the values of Energy (E=hv), alpha value, then, alphahv2 value from the UV-Vis abs data simply in exel sheet.. then plot is plotted between energy (x-axis) and alphahv2(y-axis). Afterthat, draw a tangent line for that graph, the point at which the line in the x-axis shows the band gap the material....
Yes you can use Transmittance & absorbance, BUT after you have eliminated reflectance. A standard UV/VIS/NIR spectrometer will come with all 3 set-up where you perform 2 experiments. 1. reflectance & transmittance and 2.transmittance & absorbance. From the T & A data you eliminate the R to arrive at the exact T & A values - which then yu can use to determine band-gap.
Thanks to all for their good suggestions
I learned many things and I think now I can overcome my mistakes
When not reflections take place in your data absorbance and is difficult to trace the tangent, I suggest you take the derivative of your data. See for example our recent publication MaterialsLetters139(2015)63–65.
Best regards.
Dr. Narcizo
Hi, Professor Dr. A. Kumar
You had added the answer, I need some more guidance that how to Normalize the data. I just have converted the % Reflectance data to Reflectance dividing 100.
May be for you this is very easy but I am new in research. Need your cooperation.
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