i have a confusion on this matter as i have found that some of the paper in literature says that having low intensity for PL spectra is better as it indicates good inhibition of electron and holes recombination rates. however, i recently came across few paper on La doped TiO2 which says that higher PL intensity led to higher photocatalytic activity of the catalyst as more oxygen vacancies are available. Please help me on this matter.
thank ypu .
the confusion i have is that if having low PL intensity means low recombination of electron and holes which can give better photocatalytuc activity, then the opposite would be high PL intensity would increase recombination rate and reduce photocatalytic activity. but this is not the case in the few paper that i have read, thus my question on how do you interpret the PL spectra.
Please find this journal..Review of photoluminescence performance of nano-sized semiconductor materials and its relationships with photocatalytic activity, Solar energy materials and solar cells 90 (2006)1773-1787..Hope it can help you.
For a given charge carrier density (and a given absorbance), the higher PL spectra of a bulk (without a charge extraction layer) mean lesser (non-radiative) recombination. However, if you have an extraction layer, the story is completely the other way around now.
Khozema Ahmed Ali 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
When a semiconductor has a high PL value that means it has a higher recombination rate of charges carriers which is not favorable in photocatalytic reactions
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