Exactly what happens: ZnO colloidal sol when examined the optimum excitation wavelength obtained was 327 nm but when I was analyzing from 290 nm to 330 nm I found the emission peak is showing drift. I wanted to know the basics behind this phenomenon.
If the emission wavelength shifts when you change the excitation wavelength it is because the new excitation wavelength is exciting different states that emit at a different energy.
A case where this is often seen is when you measure PL of nanocrystals with a size distribution. That can give rise to a distribution of band gaps, and hence a distribution of emissive states which may or may not be excited by a given wavelength. You can also get distributions of states with varying chemical environments, and a myriad other reasons. A good start is to see if your colloidal particles are small enough for quantum confinement. If not, maybe the effect of different surface functionalisation.
Thanks S.Parani for your kind reply but in my case it is ZnO colloidal solution transparent in appearance and I wanted to know basic mechanism behind this.
Thank you for the manuscript.
If the emission wavelength shifts when you change the excitation wavelength it is because the new excitation wavelength is exciting different states that emit at a different energy.
A case where this is often seen is when you measure PL of nanocrystals with a size distribution. That can give rise to a distribution of band gaps, and hence a distribution of emissive states which may or may not be excited by a given wavelength. You can also get distributions of states with varying chemical environments, and a myriad other reasons. A good start is to see if your colloidal particles are small enough for quantum confinement. If not, maybe the effect of different surface functionalisation.
Size distribution matters in PL when you are changing excitation wavelength but in really small. PL changes with excitation wavelength mostly when it affect on its surface morphology. In most of the cases with increased excitation wavelength, sample surface gets damage which affect on PL emission. Our paper might help you.
"Enhancement of green-light photoluminescence of Ta2O5 nanoblock stacks."
https://www.researchgate.net/publication/51254309_Enhancement_of_green-light_photoluminescence_of_Ta2O5_nanoblock_stacks?ev=prf_pub
Article Enhancement of green-light photoluminescence of Ta2O5 nanoblock stacks
Actually, this shift was significant in my case. I repeated the reading with variation in slit width and scanning rate with small variation shift was observed same with change in excitation.
How can this shift in PL emission spectra and confinement is related, please illustrate me. I mean how can we say it could be due to presence of quantum dots.
Well why QDs cause PL shifts you can read in many textbooks. Whether your sample exhibits confinement depends on whether your material has features thinner or smaller than the Bohr radius of the exciton. The latter should be available in the literature, and then you need to see how big the features in your material are.
what is the mean size of the dots? is the surface density is high?
the shift to higher energy can be produced by the state filling and/or electronic coupling between the QDs
Dear Saurav,
I hope that this paper may help you.
http://dyuthi.cusat.ac.in/jspui/bitstream/purl/1777/1/Excitation%20wavelength%20dependent.pdf
The shift in PL is mainly due to the existence of a range of particles. If you want to confirm that your materials also have a range of particles, use dialysis tube to make particle distribution in a narrow range and you will find that there is almost no shift in the PL peak position.
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