If I have nanostructure metal oxide, how can I determine optical band gap from luminescence spectra?
Unless you're observing defect luminescence the luminescence peak position is your bandgap.
Hi Ahmed,
you don't need calculate anything, the center of your peak luminescence is the optical bandgap.
PL emission do not give exact band gap. It is better to calculate it from absorbance study. The band gap calculated by PL study will always less than the original band gap.
I think Dr Dharmendra pratap has a point. PL emission is mostly affected by the polarity of the solvent system and shifted with change in polarity of solvent. On the other hand absorption spectra is comparatively much less affected by change in solvent polarity. So it would be better choice for calculating band gap.
This link may help you sir,
http://www.instanano.com/characterization/theoretical/uv-vis-spectroscopy-band-gap-calculation/
I think , by using tauc plots we can find bandgap energies for available absorbance coefficient values.
what if we have UV-visible spectra instead of DRS spectra, is it working with tauc plot. Please could you answer me.
Dear Shinwar Ahmed Idrees,
I think Tauc plot should work even if we have UV-Visible spectra.
Hello everyone,
I hope the following book chapter on fluorescence Spectrometry (https://link.springer.com/chapter/10.1007/978-981-33-6084-6_17) would be helpful for you.
Chapter Fluorescence Spectrometry
Thank you for reading and sharing it.
Thanks, for all your valuable comments. I realized nowadays that DRS or its modified form is more reliable in determining the optical bandgap of nanomaterials.
Ahmed Galal Abdelrehim When a semiconductor or a dielectric material is excited above the bandgap energy and as a result of relaxation, luminescence is observed is called photoluminescence. As a result of relaxation, if only photons are emitted, the bandgap will be a "direct" bandgap, while, if in addition to photons, phonons are also emitted, the bandgap will be an "indirect" bandgap. Since, the phonons emission is due to the defects, impurities, and dopants between CB and VB. When only photons are emitted, the relaxation is called radiative, while, when only phonons are emitted, the relaxation is called nonradiative. We can only find the bandgap energy from PL data in the case of radiative relaxation (direct bandgap). In nonradiative relaxation, when an electron passes its energy to the phonons, is called Shockley–Read–Hall recombination and when a relaxing electron passes its energy to another electron or hole is called Auger recombination. From PL data, intensity, line edge, and FWHM are the characteristics parameters i.e. higher intensity means low defect density and greater FWHM gives poor structure and vice versa. In addition to all the above, the energy bandgap calculation from PL data is subject to many limitations. For example, PL emissions do not give an exact bandgap like UV-Vis absorbance (Tauc plot). The bandgap calculated by the PL study will always be less than the original bandgap. Emission spectra are usually solvent dependent and are shifted with the change in solvent polarity due to solvent relaxation, the excitation spectra are usually preferred for bandgap calculations.
In the following video, I have explained all the above discussions in detail. Links to the files used in the Origin tutorial video have been provided in the video description. Thanks
https://youtu.be/WCPSil8uryg
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