The band gaps can be calculated via UV-Vis spectroscopy using Tauc Plots. Attached you can find one file for your assistance. Here we plot the graph between (ahv)1/2 on y-axis and hv on x-axis. a (alpha) is the absorbance calculated from UV and hv can be calculated by following way... hv = 1240/wavelength. Then you will extraplot the vertical sagments of the plot to intersect on x-axis where y-axis is zero. That value is your band gap. It might be direct or indirect depending upon the formula.

Good luck!

The direct band gap were obtained from extrapolating the straight portion of

the plot of (αhν)2 versus hν on hν axis at α = 0.

For a simply calculating, the bandgap of TiO2 is the lowest point at the absorbance edge. Then, you can calcutate following, Eg=1240/wavelength.

You may also have interference fringes, which you might need to simulate to account for. In this case you may need fitting software, which is pretty common commercially, or you can write your own (many of us have in order to account for special cases). Also if you are looking for a theoretical expression for an increasing bandgap due to increased (heavy) doping, you might want to look into the Burstien-Moss shift, which can be calculated in terms of the doping level and effective mass.

Jun Pan - Your answer is good, but you have to watch out for excitonic effects near the bandgap (especially if the bandgap is large).

Kiran,

Are you asking about how to measure the bandgap or about how to make a theoretical calculation accounting for strain, etc?

you can use parallel synthesized TiO2 to calculate the bandgap of the thin film deposited on glass plate, the bandgap of the TiO2 coated on thin film and parallel synthesized TiO2 will be nearly same.

The plot of (αhν)2 versus hν on hν axis at α = 0 gives you the direct band gap when you extrapolate the straight line fitted portion of the graph.

You can measure the band gap of a thin film by a Mathlab program. But unfortunately I have lost the program. If possible you can find it to measure the same.

Well, I have few questions here. Sorry for asking questions, instead of giving answers.

i) Kiran has mentioned the system as TiO2 and doped TiO2. Is there any way to make sure whether the case is for direct allowed, indirect allowed, direct forbidden or indirect forbidden? Because, depending on the assumption for the kind of transition, we have to choose the exponent 'n' and do Tauc plotting. Many a times, I have found that the initial part of Tauc plot seems to be straight for more than one 'n' value ( i.e. if you vary the exponent n and make Tauc plot).

ii) In the same system, can we have two kind of transitions at the same time?

iii) Recently, we synthesized some TiO2 based thin films. In few films, in Absorbance spectra, the absorption edge is very flat and in Tauc plot, there is a very small part (not enough points are there) on the high energy side which can be taken as straight..How to estimate the band gap correctly in these cases?

you can get band gap from UV-VIS SPECTRA BY PLOTTING A TAUC PLOT.YOU CAN REFER TO MY PAPER: P. G. Kale, Aneesh C. Gangal, R. Edla and P. Sharma, “Investigation of Hydrogen Storage Behaviour of Silicon Nanoparticles”, International Journal of Hydrogen Energy 37 (2011) 3741-37

In the (ahv)^(1/n) versus photon energy (hv).you need to substitute various n values and check for the good fit. If one find that the experimental curve fits for many values of ‘n’ then better not use this method to find the band gap. More over you can cross check the thickness of the film by the interference fringes at higher energy value.

Can we not use the corresponding energy of lamda max as HOMO-LUMO gap?

Dear Kiran,

As has been suggested by several the UV-Vis absorption spectra can be used for band gap measurement of a TiO2 thin film and its complexes (composite?).

It is not very clear what you mean by the term "complexes". Are your films a homogeneous mixture of two materials, or TiO2 doped with some other element, or its a new compound reaction with other material?

In case of a mixture (I mean composite), you can get two band edge absorption corresponding to the two materials. In case of a doped TiO2 film, you will get single absorption edge (shifted from the band edge of TiO2) and you will get a completely different band edge in case of a new compound.

Hello, Please see our articles where we have calculated the band gap of TiO2 thin films from UV-Vis spectra. Hope, it would help. Please dont hesitate to ask again in case of confusion.

Article Characterization and hydrogen gas sensing properties of TiO2...

Hello, Please see our articles where we have calculated the band gap of TiO2 thin films from UV-Vis spectra. Hope, it would help. Please dont hesitate to ask again in case of confusion.

Article Effect of Post-Deposition Annealing Treatment on the Structu...

The answer submitted by Muhammad Ihsan

The answer submitted by Muhammad Ihsan is the best

You can take UV absorption, by using simple equation

band gap (eV)= (1240/absorption wavelength nm)

hope this will help, mean while for more accuracy you go for tauc plot.

I still don't find clear answer of my question no. (iii).

I dont use glass substrate! instead I use quartz, then I go with thin film attachment in UV-Vis spectrometer or simply put the plate instead of cuvette.

One simples method is to consider the absorption onset (departure from zero in the second derivatives of the absorption spectra) to

define the optical gap ( eV) since it is

the minimum energy where an optical absorption occurs

and corresponds to the transition between the upper and

lower edges of the conduction and valence bands.

The UV-Vis spectrum of TiO2 can be used to measure the band gap energy of this semiconductor. Just note the highest peak and then using the Plank’s quantum theory the band gap energy can be calculated as

E = hc/λ

Where h is the Plank’s constant, c is the velocity of light and λ is the wavelength (in nanometer) of absorption.

Dear Mr. Shejale,

You could read the paper of Changsi&Feng (L. Changshi, L. Feng, Opt. Commun., 2012, 285, 2868) where you will find details of a really reliable method for this purpose.

Antonio Eduardo H. Machado

Universidade Federal de Uberlândia

Many Authors have suggested references, so I need not refer to our Papers, already on Research Gate. It is so simple.

The optical band gap can be calculated from the absorption coefficient “alpha” applying so called power low making the plot of (alpha*E)^n vs. E (E is photon’s energy) and extrapolation of (alpha*E)^n to 0. First step of this procedure is to determine the spectrum of imaginary part of complex refractive index or so called extinction coefficient, k. The value of the extinction coefficient can be calculated from UV-Vis-NIR specrophotomeric or ellipsometric measurements. The absorption coefficient “alpha” can be calculated by simple equation “alpha” = 4*pi*k/(lambda). “Lambda” is wavelength.

The second way for calculation of “alpha” is from UV-Vis-NIR specrophotomeric using transmittance, T and reflectance, R spectra. Most often using formula is “alpha” = -1/d (1-R)/T. (d is film’s thickness). This formal is valid only in case if “alpha”*d > 1. If the film’s thickness is smaller for other relation of “alpha” with transmittance, T and reflectance, R, you can found in T.S. Moss, Optical Properties of Semiconductors, Butterworth, London (1959).

The power factor n possesses different values for allowed direct and indirect or forbidden direct and indirect transitions.

Are there any method to calculate band gap of thin film by other method except of Uv-Vis like FTIR or XRD or...?

You can find a discussion of band gaps of TiO2 rutile and anatase in

Phys. Rev. B 82, 045207 (2010).

or

http://journals.aps.org/prb/abstract/10.1103/PhysRevB.82.045207

You need to consider the nature of the band gaps that you are searching for (direct vs indirect; electronic vs optical). It is not straightforward even for the bulk materials.

Hojjat, You can use cyclic voltammetry.

Hi

may some one help me to get the energy gape from uv-vis

i sent file in origen

Hi Hussam, after you calculate abs. coefficient alpha from A, you need to plot a graph with (αhµ) to the power 'r' in the Y axis vs hµ (eV) in the X-axis and extrapolating the linear portion to [(αhµ) to the power 'r' ] = 0:. The value of the exponent 'r' will depend on the nature of transition. It is '2' for direct, allowed transition. Please refer to our paper: Journal of Crystal Growth 261 (2004) 77–81.

THANKS FOR ALL

but is the value of the absorption is the max value of y axis (in Abs.-wavelength) curve some one may open the above attachment file and do this using origin software

Hassam, you need to take the value of A and calculate alpha from 369.8 nm towards higher wavelength. Then plot the graph with (αhµ) to the power 'r' in the Y-axis with wavelength (nm) in the X-axis. Your Abs. curve is shallow, does not show a strong fall in the low wavelength region and so, the extrapolation is likely to yield quite low value of Eg. Do you expect such low value?

thanks for all i did and get the Eg

i will send how to calculate theEg step by step using origin

nice Hussam Musleh

İnformation is attached in pdf. 

The paper provided by M. Celalettin Baykul is very useful in calculating Eg.

There is a templete you can apply on it but is complicated so far. i tried it and the results were positive

see the application note:

Simple Method of Measuring the Band Gap Energy Value of TiO2 in the Powder Form

using a UV/Vis/NIR Spectrometer

After you measured the UV-vis-NIR absorption spectrum, you can take the wavelength as the the absorption intensity start to take off .Then you can calculate the band gap energy by using equation: Eg (eV) = 1240/(wavelength in nm). For example, if the intensity arises from the baseline at 340 nm, then you have a material with band gap of 3.65 eV.

All of the above is well and good but there are a couple of caveats:  (1)  In my experience most TiO2 preparations are indirect band gap, so the spectrum must be analyzed accordingly; (2) if the deposit is polycrystalline its extinction may include a significant scattering component so the observed spectrum may require Kubelka-Munk analysis to extract the "true" absorption spectrum.  

The actual formula for calculating band gap is Eg= hc/ λͅ , 

3.2. Optical properties of semiconductor thin films

The optical absorption spectra of semiconductor thin films must be obtained

in the wavelength range 300 to 600 nm. The optical absorbance can be

measured from these spectra. According to Tauc, the dependence of the

absorption coefficient α on the photon energy hν for near- edge optical

absorption in semiconductors takes the form

(αhv)1/m =k(hv-Eg)

where Eg is the optical band gap, k is a constant and m=1/2 for an

allowed direct energy gap and m=3/2 for a forbidden direct energy

gap. In order to determine the optical band gap of a semiconductor thin film, taking m=1/2, (αhν)2 must be plotted versus hν using the

data obtained from the optical absorption spectra. The direct band gap

of the semiconductor thin film is obtained by extrapolating the linear

part to the zero of the ordinate.

thanks

is Taucs relation valid for crystalline films only?

can we use it for semi crystalline films also?

band gap energy formula Eg = 1240/λ ( wavelength)....

Thank you for reply Mr. Kiran

The formula you mentioned is for energy which is hc/λ.....not the band gap energy....

Thank you Omed for reply and its very useful...

i would like to calculate the band gap of polymer sample using simple uv visible spectrometer. is it possible to calculate using following graph....

The graph you have shown in the image is of Absorption vs Wavelength. For Band gap measurement we have to plot Absorbance square vs Energy... Another point that graph you have shown it is of dual band gap material because this have two absorption peaks..so its band too double..

1.  Kiran--you must be careful that you have actually measured absorbance and not extinction; the latter may be artifactual insofar as it includes components from multiple reflections at the air-sample interface and the sample-substrate interface. The geometry of your measurement is critical here. An alternative approach would be to place the sample against a white background and measure the reflectance spectrum; then calculate the absorbance component using the Kubelka-Munk transform.

2. Vaishali--Ravi may not be quite correct. One of the two transitions you observe may be to (or from) a localized surface or impurity state and not associated with the bandgap at all. The question is which one. If the lower energy transition is the bandgap transition then the procedure described in Ohmed's answer can be followed. If it's the higher energy transition, then the two components need to be deconvoluted. One can do this on the assumption that the lower energy transition gives rise to a Lorentzian absorption envelope...but that's a big assumption.  You might get some guidance from a computational chemistry study of your material.

 Hi all, 

I find this discussion so helpful to me. I have some problems in calculating the band gap for MgO incorporated TiO2 which shows two peaks. one for TIO2 and another for MgO. But my problem is, the absorbance value changes even though i have prepared the samples by dissolving same amount of the MgO-TiO2 precursors. Can i take the absorbace value as it is to calculate the alpha value?  

With reference to your statement, I want to ask you one thing: two peaks in which plot?

@suchitrs sen ... The two peaks were observed in the plot of absorbance vs. Wavelength.

However, when i plot for ahv vs hv the curve seeems smooth.

here is the excel file which will plot the alpha hf square calculated from dffuse reflectance spectra for some _______semiconductor to calculate the band gap

With UV- Vis data you can use the Tauc's plot. 

Magnetic fault current limiter

You can use the relation 1240/cutoff wavelength obtained from the absorption spectra.  Perkin Elmer is adopted this approach. 

Here you can find good explanation and band gap calculator,

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

If your sample is transparent. You can use UV-Vis spectrophotometer. You can get the data which is the plot of absorbance versus wavelength of the light. from  UV-Vis spectr. Then, using the Tauc method. You can determine the band gap. But unless your sample is not transparent, you can use the photoluminescence technique.

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

I had given the answer already to that question. But again You must use UV-Vis spectrophotometer. You can get the data which is the plot of absorbance versus wavelength of the light from UV-Vis spectr. Then, using the Tauc method. You can determine the band gap. Again If the thin film on the substrate, is transparent you get the Absorbance spectra. So from the plot of absorbance vs wavelength of the light will be used as data in the TAUC method. I suppose that you know what the TAUC method is. Unless you konow how you use TAUC law you can look at my paper. The title of my paper is "AFM and SEM studies of CdS thin films produced by spray pyrolysis method". microlectronic engineer which was published in 2000.

you can use the UV-Vis spectrum to calculate the band gaps of semiconductor material (allowed direct, allowed indirect, forbidden direct, and forbidden indirect transitions), by plotting the graph between (alpha hv)^(1/n) versus photon energy (hv).

where alpha : is the optical absorption coefficient, which can be calculated from absorbance(A), and thickness of the sample(t) using: (alpha=2.303A/t); and (hv) can be calculated form wavelength using: (hv = 1240/wavelength); The power factor (n) takes the values of (0.5, 2, 1.5, and 3) for allowed direct, allowed indirect, forbidden direct and forbidden indirect transitions.

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

Gap energy can be obtained from Tauc plot base on UV-Vis data (transmittance v.s. wavelength). Somehow, the researchers use Tauc equation:

(alpha) hv =  A*(hv - Egap)^n

where: 

alpha = linear absorption coefficient; h = Planck's constant; nu = frequency of light; A = the proportionality constant; Egap = gap energy; n = 1/2 for direct band gap material.

i have got two different band gap values of same data in transmittance mode and absorption mode.i am unable to understand how  to solve this issue.

anyone kindly help me

can you please help me, is the above same formula work for colloidal nanoparticles? if in the case of colloidal nanoparticles of absorption spectra, how much thickness I have to consider? Thank you.

pls see the file

 Dear Mr. Azad Kumar

There is no file attached. Please re-upload the file/article. Thanks in advance.

The direct band gap were obtained from the plot of (αhν)2 versus hν, then extrapolated the straight portion on hν axis at α = 0.

If you want to calcualte the band gap of any semiconductors materials, Firstly you should take any one of the data for the Transmittance, Reflectance or absorbance using UV-Vis spectrum to calculate the band gaps of semiconductor material. After taking any one readng for those of those then you can calculate absortion coefficient, α=-ln(T)/t , α =(ln [(1-R)2/T]/t where, T, R and A are the transmittance , absorbance and reflectance, t is the thickness, respectively. After gatting absorption coefficient then you can use Tauc equation: (αhν)= A*(hv - Eg)^n

where A is constnat and n is the index number or power factor, for n=0.5, 2, 1.5 and 3( allowed direct, allowed indirect, forbidden direct, and forbidden indirect transitions). using this equation you can plot (αhν)2 vs photon energy (hν) for allowed direct band gap and (αhν)1/2 vs photon energy (hν) for allowed indirect band gap and extrapolation the straight line portion of the curves to zero absorption coefficient value gives the energy band gap value (Eg).

thanks alot

guys, what if my sample is liquid? does it works with liquid?

In the name of God

For calculation of Band gap energy of semiconductors and insulator materials ,you need a UV-Vis. absorbance spectrum of your samples.Then ,using Tauc equation the band gap energy will obtained.

you can use the following references for band gap calculation:

,RSC Adv., 2014, 4, 59764–59771.

Thin Solid Films 516 (2008) 4953–4957

Dear Alireza Goudarzi,

thank you very much for your help,

I appreciate it so much.

dear I wants to asked one questions that how we calculate band gap for powder every thing is ok but what value we put for thickness

This article will be helpful.

Hi All,

I am just wondering whether anyone of you can help to determine the band gap from the attached data. I took the solid-state UV-VIS reflectance data. Then Used Kubelka-Munk theory to get direct or indirect band gap. This data seems like much more complex compared to other materials. Also, can I determine whether it is direct or indirect from this UV-VIS reflectance data? Is there possible multiple band gap? you can send me email: [email protected]

dear all, just read this information in this link below

........

Article The calculation of band gap energy in zinc oxide films

maytham

Following articles will be helpful for you.

http://iopscience.iop.org/article/10.1088/1361-6528/aacee0/meta

Article Facile one-step economical methodology of metal free g-C3N4 ...

Article Synthesis of Environmentally Encouraged, Highly Robust pollu...

Tuac calculation

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

You can measure absorption of the thin film on the glass by UV-vis spectrometer. Then, you can calculate the band gap using the Tauc plot.

The optical band gap of semiconductor can be estimated from the intercept of the extrapolated linear fit for the plotted experimental data of (αhν) n versus incident photon energy (hν) near the absorption edge.

thans

You can use taux plot: by tthe estimation from thé interceptions of thé extrapolated linear fit for thé plotted expérimental data of (alpha.h.nu) n versus incident photon energy near thé absorption edge

Or by the différentielle reflectance.

Whats wrong in just using E=hc/lambda, and get the energy in joules and then convert it to eV ???

Plot the Tauc Plot for the absorbance. Slope of this will give you the energy gap

You can follow

ArticleThe calculation of band gap energy in zinc oxide films

simply with the help of Solid state UV spectra (DRS). Plot the Tauc plot and the slope will give you the band gap energy.

Plot the Tauc plot and the slope will give you the band gap energy.

Tauc plot is a good one for this aspect

You can look into the following article:

Article Optical Properties and Electronic Structure of Amorphous Ge and Si

How much is the index of m for MWCNT, GNP , GO and SWCNT in the attached equation?

Dear Kiran,

In order to obtain information about the energy band gap of TiO2-Ge and also about the influence of deposition conditions the absorbance spectra of the thin films with different content of Ge were recorded. The optical absorption edge was analyzed with Tauc equation ,

αhν= A(hν-Eg)m……………………….Equn…1

where A is the optical constant, α is the absorption coefficient, Eg is the optical band gap and m value is 1/2 for direct transitions and 2 for indirect transitions.

The direct band gap energy Eg of 3.6 eV, can be calculated using Tauc Eq. for m=1/2, from the intersections of the straight line with the energy axis.

Hope it is helpful for you.

Ashish