Undoped and Ni-doped (3%, 6%. 9%, 12%) ZnO NPs were synthesized by the facile reflux method. The optical absorption properties were studied by UV-vis sectrum using same concentration.
Dear Sajith Dananjaya :
The more nickel ions penetrate into the lattice of zinc oxide, the greater the intensity of the absorption. See file
Best regards
Dear Dananjaya,
1) What is loading of NPs in each case? Are they all the same? Often, there can be an optimum loading (i.e. 9% doped).
2) Do you know the particle size of these NPs. there can also be an optimum particle size beyond which ZnO sediment.
These two factors can have a significant influence on the optical absorbance of NPs suspended solution.
3) Are Ni percentages in wt% or at%. (If wt%, at higher wt% it may form NiO/ZnO mixed phases instead of doping). Also, if the quoted dopant levels are wt%, it is more likely that you have a NiO/ZnO composite or mixed phase(s) which could influence the degree of suspension which effect optical absorbance.
4) In related to the point (3) above, there does not appear to be a shift in the band gap with doping, thus we would assume that Ni dopants have not gone to the ZnO lattice.
5) Finally, the degree of suspension is directly related to the surface properties of NPs which should not be ruled out in your consideration.
Hope this helps.
Kind regards,
Upul
Dear professor
Thank you very much for the all the answers. I got the XRD pattern for undoped and 6% and 9 % Ni doped ZnO NPs. It is clear that there is no NiO peak and not change the crustal structure with Ni doping. But, 6 % Ni doped ZnO XRD peaks shift to lower angle as compared with a pure ZnO NPs. However, 9% Ni doped ZnO XRD peaks shift to higher angle as compared with a pure ZnO NPs. Can we used this shift to ex-plane the above spectrum?
PXRD reflection shift generally indicates a crystal lattice shrinkage or enlargement by impurity atoms. A higher 2θ shift compared to the pristine material signifies lattice shrinkage, whereas a low shift shows an enlargement. Often, doping reduces the crystallinity of the pristine PXRD reflections with a significant peak broadening.
Therefore, in this case, I would expect a peak broadening along with a shift towards a higher 2θ angle upon doping (this effect is pronounced at higher doping levels).
Hope this helps..!
Subhashi
Dear Subhashi
Thank you very much for the valuable answer. How we explain the XRD peak shift to lower angle with doping ?
It is strange that you observe a shift towards lower 2θ angle for the 6% doped powder. Have you observed any peak broadening in that diffractogram compared to pristine ZnO?
Yes. Both 3% and 6% Ni doped ZnO shift to higher angle. But 9% and 12 % shift to lower angle. There is many papers, explaining the both direction of shift (separately) with Ni doping. I need clear explanation for the lower angle shift ?
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