Hi Anil,

To calculate the band gap, you need to follow the following steps.

Plot the graph between (ahv)^(1/n) versus photon energy (hv).

where a: is the optical absorption coefficient,

To calculate "a" you need to use following relation (a=2.303A/t)

where A is absorbance and t is thickness of the sample.

For calculation of hv, you can use (hv = 1240/wavelength)

wavelength can be seen from the absorbance graph

The value of power factor varies for different sample

n = 0.5 for allowed direct transition

n = 2 for allowed indirect transition

n = 1.5 for forbidden direct transitions

n = 3 for forbidden indirect transitions.

Now, extrapolate the straight line portion of the curves to zero absorption coefficient value gives the energy band gap value.

Hope, this is beneficial for you.

regards

raeesh 

Thanj You Raeesh Muhammad sir..it is helpful for me

You can substitute the absorbance data in the excel file which contains conversion function already and correspondingly you will  get the the data of tauc plot in other two columns. if you have already got then it is fine otherwise i can provide you if you needs.just intimate me

https://www.instanano.com/2017/01/uv-vis-spectroscopy-band-gap-calculator.html

Anil Arya

Tauc used an equation in 1968 to calculate the absorption edges (bandgaps) of amorphous Ge and Si from their absorption data.

(αhν)γ=A(hν-Eg)

In this equation, α is the absorption coefficient, h is Planck’s constant, υ is the frequency of the incident photon, A is a proportionality constant (which is determined by the index of refraction, electron, and hole effective masses; however, it is usually taken as 1 for amorphous materials), and Eg is the bandgap energy. The important term is the exponent γ, which denotes the nature of the electronic transition, that is, when γ=2 it is a direct allowed transition, and when it is equal to 1/2, it is an indirect allowed transition. For γ=2/3 it is a direct forbidden transition, and for γ=1/3 an indirect forbidden transition. Typically, the allowed transitions dominate the basic absorption processes, giving either direct or indirect transitions.

Thus, the basic procedure for a Tauc analysis is to acquire optical absorbance data for a sample in question that spans a range of energies from below the bandgap transition to above it.

Plotting the (αhν)γ versus (hν) is a matter of testing γ=2 or γ=1/2 to compare which provides the better fit and thus identifies the correct transition type.

I have provided the Template file (Origin file) in the video description. Thanks

https://youtu.be/LLESVSsZmlg