How to calculate band gap energy from UV-Vis reflection (DRS) data in origin

[@ashfaqahmad2987]

Thank u so much, dear sir. You have set aside a few minutes for the day's task.

[@SAYPhysics]

Thanks for the appreciation dear 😊

[@mayernashat446]

You have helped me in my graduation project. God bless You.

[@SAYPhysics]

Thanks for the acknowledgement. Please share it with others as well.

[@kumarshivesh4336]

Thanks, Dr. Shahid Ali Sir for another useful video on bandgap calculation.

[@SAYPhysics]

Thanks dear for being in touch.

[@kumarshivesh4336]

@@SAYPhysics Your videos are beneficial for my current manuscript, based on the synthesis and characterisation of metal oxide nanoparticles. I'll keep in touch with you.

[@SAYPhysics]

Yes, sure. You're welcome

[@Almeidov]

Thank you so much. Very good explanation.

[@SAYPhysics]

Thanks for the appreciation 😊 and you're most welcome dear.

[@yuwarajkhatri7585]

The bandgap seems to be wrong because the origin of the vertical axis has not been set at zero. Vertical axis MUST start from zero. Otherwise the tangent line intersects the horizontal (eV) axis at a point less than the actual bandgap.

[@SAYPhysics]

You're principally right, and in my case thee difference isn't more than 0.01 eV However, for a simplest case this is true only. In this playlist, I have a bunch of videos on the brandgap, you may watch them to get idea about some complex cases.Thanks

[@Kasen-l3c]

Thank you for your explanation. I just have one more question. If my material is direct, should I use (F(R)hv)2 or (F(R)hv)1/2? It should be the former one according to the absorbance video but there is no specific explanation in the reflectance one. It should be the same right? Thank you!

[@ibrahimnazemqader9153]

Thanks. The minimum y-axis should be 0, then the extrapolation line is correct.

[@SAYPhysics]

Yes, you're right, provided offsets are not involved. Thanks

[@MuhammadIsmail-yq4qq]

Waiting for QM lectures Which subject u will upload in this semester

[@SAYPhysics]

In a month IA, we'll start uploading from Lecture 51 onward, as per Griffiths book content. Thanks

[@MuhammadIsmail-yq4qq]

@@SAYPhysics also upload another course in parallel to QM

[@SAYPhysics]

Yes, I'll in relativity, IA

[@antonioculebro8038]

Sir, I have an existential doubt and I would really appreciate your prompt response, why are the units Ev*cm-1? I am confused, the wave number is the inverse of the wavelength, but when dividing 1240 / nm, we do not have Ev*cm-1, please explain to me. :(

[@SAYPhysics]

The units of eV·cm⁻¹ may have caused some confusion. When you divide 1240 by the wavelength in nm, the result is in eV, not eV·cm⁻¹. The factor 1240 comes from converting between energy in eV and wavelength in nm (since 1 eV ≈ 1240 nm for photons). The term "cm⁻¹" refers to the wave number, which is the inverse of the wavelength in cm. If you're calculating the band gap in eV, you don't include the "cm⁻¹" unless you're specifically converting to wave number. Thanks

[@antonioculebro8038]

@@SAYPhysics Thank you very much doctor, but then, why in the video in the bandgap graph the y-axis has units of ev*cm-1, if the conversion was not made? 🥹

[@SAYPhysics]

@antonioculebro8038 because on the y-axis, we don't have energy but alpha hv. The cm-1 comes there due to the absorption coefficient alpha. Thanks

[@thephysicspoint]

Nice, elaborated, and to the point.

[@SAYPhysics]

Thanks for the appreciation dear

[@namrathanammu4899]

Hello Sir, I'm Namratha from India. Now I have started my PhD journey. For UV-related things, I always refer to your video. I wrote one paper(UV part) based on your Tacu plot video. Thank you for sharing your knowledge. I have one doubt in this video. I have wavelength and reflectance, and I can find an energy gap. But can I calculate absorbance from reflectance? I referred many papers but I didn't get the answer. One says it's A=1-T while others say it's A=1-(R+T). Here I don't have the transmittance and absorbance data. How can I calculate absorbance? In case we don't calculate absorbance from UV DRS data. Can you please send me one research paper that includes all your explanations? I need to write the reference.

[@SAYPhysics]

Hi Namratha, thank you so much for your kind words! I'm glad to hear my videos have been helpful for your research. Regarding your question about calculating absorbance from reflectance, you're right that different sources provide slightly different approaches. When dealing with reflection (R) and transmission (T), the general formula is (A = 1 - (R + T)). However, in cases like UV-Vis DRS where you don’t have transmittance data, the common approximation is (A = 1 - R), especially for opaque or highly scattering samples. This is widely accepted for such cases. If you are only working with reflectance data, you can apply this approximation, assuming the transmittance is negligible. For further reading, I suggest looking into papers that cover Kubelka-Munk theory, which is often used in DRS analysis. It provides a good explanation of how reflectance can be related to absorbance. Feel free to ask more questions if needed, and best of luck with your PhD!

[@namrathanammu4899]

@@SAYPhysics Thank you so much sir. And i couldn't find UV DRS for fibres. fibre is a non conducting material. But im getting 3.80eV energy gap value. I think it is incorrect. can you please suggest one paper which includes UV DRS of a fibre?

[@SAYPhysics]

Thank you again for your questions! I understand your concern about the 3.80 eV band gap for a non-conducting fiber material. It does seem high, especially for typical fibers, which are usually insulators or semiconductors, depending on their composition. Fiber materials like polymers often have lower band gap values, usually ranging from 2.0 to 3.5 eV, though there can be exceptions depending on the specific material. For UV-Vis DRS measurements, the Kubelka-Munk theory is indeed a useful approach to consider. It relates reflectance to absorbance, particularly in scattering samples, and can give a more accurate determination of the band gap for non-transparent materials. In your case, with fibers, scattering is likely significant, and using the Kubelka-Munk function (F(R)), where (F(R) = (1 - R^2) / 2R), may provide better insight than directly using the approximation (A = 1 - R). Regarding your energy gap value, it’s possible that the value you are obtaining might be influenced by the scattering properties of the fiber or an incorrect assumption about the reflectance spectrum. Verifying the reflectance data with a Kubelka-Munk transformation could give you a more accurate band gap estimation. As for research papers, while there may not be a paper that exactly fits your fiber material, I recommend looking into studies that apply UV-Vis DRS with the Kubelka-Munk method for non-conducting materials, like polymers or oxides.

[@Powolice]

since both the direct and indirect bandgap looks the llinear you concluded that this is qusai direct bandgap then use indirect bandgap. Is this always true where when the direct and indirect looks the same linear you use indirect bandgap?

[@SAYPhysics]

In general, when both direct and indirect bandgap data appear linear, it's safer to use the indirect bandgap for calculations. This is a common practice to ensure more accurate results in cases of ambiguity. Thanks

[@wazirs_world]

Sir well explained 🤗❤

[@SAYPhysics]

Thanks dear

[@wazirs_world]

My plxr sir ❤

[@MrMRbarati]

Excellent presentation. Thanks for sharing and deciding your time to learn us. God bless you. 🙏🌸

[@SAYPhysics]

Thanks for the appreciation dear. I really enjoy doing these. Aameen

[@shwetachahal6667]

Can you explain the extra drop in ahv1/2 and ahv2 on higher hv value? I didn't get it

[@SAYPhysics]

Would you please let me know the exact location of the video so that I can respond accurately to that. Thanks

[@organiccookingmore9071]

good.. dear I have absorbance data from uv spectroscopy... can I convert this data into reflactance and solve it for and gap

[@SAYPhysics]

Yes. Check the following playlist which has some videos on this. Thanks Bandgap Calculation in Origin: kzbin.info/aero/PLeWSImvDbplfORnYYdjb0DLiLpyi7VWY1

[@organiccookingmore9071]

@@SAYPhysics it is very well explained.. but sir actually I have absorbance data and I want to convert it into reflactance... is it possible or not?

[@SAYPhysics]

I told you Yes. With the help of K-M function, you can do so, as explained in these videos. Thanks for the appreciation 😊

[@organiccookingmore9071]

@@SAYPhysics but there is no video in which absorbance A is converted into Reflactance R... in K-M function the parameter is R which means we need reflactance.. but issue is that I have absorbance vs wave length data

[@organiccookingmore9071]

sorry for so many questions

[@montserratdelahoya4410]

What does F(R) means physically? It's the ratio between k/s but, what is that?

[@SAYPhysics]

In addition to my explanation in the beginning of the tutorial, let me add that K is the absorption coefficient, and S is the scattering coefficient. However, due to the difficulty in measuring the absolute reflectance R∞, in practice, the comparative reflectance r∞ with respect to a standard powder of which K is near zero (0) in the actual measurement range. Thanks

[@areejfatima2807]

@@SAYPhysics If F(R) = K/S , Then how are you putting cm with eV in the unit on y axis.

[@SAYPhysics]

In the first 5 min part of the tutorial, I'm explaining all this. If your confusion yet continues, let me know, I will elaborate it further. Thanks

[@areejfatima2807]

@@SAYPhysics How absorption co efficient have unit per meter? If this is from R . Then R is simple the ratio of reflectance fromt the sample to standard. So it should be unitless.

[@SAYPhysics]

@areejfatima2807 Absorption Coefficient (α) is measured in units of cm-1. This is used when dealing with the Beer-Lambert Law in contexts where concentration is not expressed in molarity. It's a measure of how much light is absorbed per unit path length. Thanks

[@mushahidhussain2460]

Wonderfull Sir, Sir kindly make vedio to calculate Response and Recovery time, and hysteresis loop calculations.

[@SAYPhysics]

Thanks for the appreciation dear. Sure, I'll do so as per my schedule tutorials.

[@mushahidhussain2460]

@@SAYPhysics thank you sir waiting for your lecture

[@SAYPhysics]

Sure dear. Thanks

[@snehareddy4826]

Hello, thanks for the video. Is this method applicable for specular reflectance? Also, From the tauc plot (alpha h v)2 vs (hv), how can we measure the energy band gap if we have multiple peaks? I mean it’s difficult to choose a point to extrapolate if we have multiple peaks. So, how can we decide?

[@SAYPhysics]

Thanks for the appreciation dear. In multiple peaks, you may choose the first one as a band edge. It's a diffused reflectiance . If your material is a modified perovskite, it possess different bands corresponding to different energies.

[@snehareddy4826]

@@SAYPhysics If I choose first one as the band edge, it results in very low band gap. I work on ferroelectric (PLZT) thin films for photovoltaic applications. Yes, it’s a perovskite material. I could measure the specular reflectance on my films using UV-VIS. Is this method applicable only for diffuse reflectance?

[@snehareddy4826]

@@SAYPhysics If it has different bands corresponding to different energies, then how can we put the accurate band gap? The PLZT material has a bang gap (3-3.5 eV). I was considering the peak within that range. But I am not sure if it’s the right way to do. I can share the data with you if you want to look at it.

[@snehareddy4826]

@@SAYPhysics please respond.

[@SAYPhysics]

For such materials, you can't use the familiar R+A+T=1 equation to get reflectance (which is specular in nature). You need to have DRS data, and then use the guidelines provided in this video. Thanks

[@soniaahlawat9130]

How can we find which band gap is correct( direct or indirect) ??

[@SAYPhysics]

In UV-Vis spectroscopy, direct bandgap materials typically exhibit sharp absorption peaks, while indirect bandgap materials show broader absorption bands. By analyzing the shape and intensity of the absorption spectrum, along with theoretical modeling, you can determine whether the bandgap is direct or indirect. Additionally, plotting the absorption coefficient versus photon energy can help identify the nature of the bandgap. That's, we will check in which case a steep knee is formed. If for both 1/2 and 2, a steep knee is formed, it will mean it's a quasi band gap ie both direct and indirect. Thanks 😊

[@kagakuyy4311]

what the significant different ahv2 and ahv1/2, sir?

[@SAYPhysics]

This decides about the directi and indirect bandgaps, respectively. Thanks

[@gauravrajak007]

some people asking about the normalizing of K-M functions in comments, why do we need to normalise and when to.

[@SAYPhysics]

When we're only to decide about the location of a peak or its shifting, it's better to normalize the KM values. In the case of intensity discussion, we avoid to normalize as the data loses its importance then. Thanks

[@syedraza6108]

How can you calculate energy in ev where is the absorption A?

[@SAYPhysics]

Thank you for watching the video! I've included all the necessary details and calculations in the video description. You can find an Excel template there that demonstrates how to calculate the band gap energy from UV-Vis reflection (DRS) data, including the absorption (A) values. Please check it out, and if you have any further questions, feel free to ask. Thanks again for your interest.

[@sayraruvalcabamanzo9419]

How can I normalize the K-M function?

[@SAYPhysics]

Take the data in a separate column and apply the normalization as 0-1 or 0-100. Inside my playlist, You'll find some videos on the normalization. Thanks

[@mbusiprimemafu2155]

after processing the data how do I analyze the data

[@SAYPhysics]

The video explains how to get values for explaining/analyzing your data. I'll soon explain in another video how to interpret UV-Vis data, once all the values extraction is completed. Thanks

[@MuhammadIsmail-yq4qq]

Plz sir start QM lectures my 7th semester is start

[@SAYPhysics]

From tomorrow IA we'll start uploading relativity lectures and then in a month the QM. Thanks

[@nadaaliya4229]

where does 1240 come from?

[@SAYPhysics]

It's based on some calculations which I have done in detail in the following video tutorial. Thanks kzbin.info/www/bejne/gn2ohImJqL-gosk

[@gauravrajak007]

thank you very much

[@SAYPhysics]

You're welcome dear

[@rosezroseful]

Hello, i am using origin 8.5... In this how to insert f (x) row??

[@SAYPhysics]

You're using an old version. The f(x) insertion is available in version 9.0 and above. However, you need not to worry that I have already uploaded a video on how to legally install the latest version of OriginLab. Thanks kzbin.info/www/bejne/gpLQc6SQl7hmfJI

[@parimalasowmianarayanan5203]

thank you very much

[@SAYPhysics]

Welcome dear 😊

[@sayraruvalcabamanzo9419]

How can I normalize the K-M function?

[@SAYPhysics]

Take the data in a separate column and apply the normalization as 0-1 or 0-100. Inside my playlist, You'll find some videos on the normalization. Thanks

[@sayraruvalcabamanzo9419]

@@SAYPhysics Thank you, although I need a procedure for the normalization of K-M function with respect to Reflectance for the transmittance obtention.

[@SAYPhysics]

Right. You can send me your data on [e-mail] if the videos are not helping you. Thanks