I have synthesised quantum dot using green synthesis. Uv vis spectra show peak at 270 nm(protein peak) and 400nm(quantum dot peak). Excitation wavelength for PL measurement is 390nm but i get broad spectra. What is the reason behind this.
Saqib Khan can you share your PL result ? It might be helpful for those who can help you with it.
Dear Saqib Khan! Usually in the same conditions the reason for the broadening is the wide difference in the QD sizes.
Dear Saqib Khan ,
I would like ti second the colleague V. B. Zaytsev that the major cause may be the presence of size variations in the quantum dots. You can naturally verify the size of the quantum dots by electron microscope or any grain size measuring equipment.
Best wishes
Abdelhalim abdelnaby Zekry V. B. Zaytsev
Thank you for your responses.
TEM results show that QDs range from 3.5 nm to 4.5 nm. Will this difference in QDs give broad spectra of PL? plz give references to any journal paper if possible, it will be very helpful.
Depends on the QD material. See for example
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwj5gZnWupX3AhXLlYsKHX62BFsQFnoECAMQAQ&url=https%3A%2F%2Fwww.researchgate.net%2Ffigure%2FVariation-of-quantum-dot-energy-bandgap-vs-dot-size-for-some-common-semiconductors-From_fig2_329660341&usg=AOvVaw1kTih3p6cCM1GqKya7wX6_
Dear Saqib Khan ,
please follow the paper in the link: Article Broadening of Photoluminescence by Nonhomogeneous Size Distr...
Best wishes
Abdelhalim abdelnaby Zekry V. B. Zaytsev
thanks a lot for your quick response.
I still did not figure out the actual reason.
here I am attaching the PL graph of QDs.
Dear Saqib Khan! At your graph I can see a very standard PL spectrum for QDs (cadmium сhalcogenides for example).
The exiton line is narrow enough. You probably are interested in the nature of the wide long-wavelength band of the spectrum? This line is due to the luminescence of the surface defects on the QDs. It is absolutely usual. Many researchers are working on passivation of thеsе defects. Though it is possible to use this wide band: https://www.researchgate.net/publication/339367206_Highly_luminescent_copper-doped_ultrathin_CdSe_nanoplatelets_for_white-light_generation
The range of your QDs size from 3.5 nm to 4.5 nm is responsible for the width of the exiton line near 390 nm
Dear Saqib Khan ,
I completely agree with my colleague V. B. Zaytsev .
The PL at the right of the narrow spectrum is due to the emission of the background material in which the nanograins are imbedded.
Best wishes
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