The characteristic wavelength of ZnO is supposed to be ~380 nm. However, in this article1, the peak has been blue-shifted to 214 nm. This is quite similar to my sample where the peak is at 200 nm. In the article it is said that:

the blue shift may be due to the transition of electrons from the inner shell of copper to the outermost shell as time passes. It is possible that, due to aggregation and agglomeration, particle size increases and material settled down on the bottom of the container causing decrease in absorbance.

Could someone explain what this means?

Also, I did a UV-dr on the sample and it gives me a peak at 380 nm.

1: Structural and Optical Characterization of ZnO Nanoparticles Synthesized by Microemulsion Route. International Letters of Chemistry, Physics and Astronomy 2013, 14, 26-36.

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    $\begingroup$ Where possible, include human readable citations rather than links to reprints. Doing this ensures that if the website changes/removes the PDF file that the original article can still be found by future users of chem.SE. $\endgroup$ – NotEvans. Jul 21 '17 at 11:39
  • $\begingroup$ I think the term "hypsochromic shift" is more applicable here. $\endgroup$ – andselisk Jul 21 '17 at 11:47
  • $\begingroup$ 1} Are you taking into account that the peak at 214 nm is possibly explained by the presence of Cupper? Is it Cu present in your sample? 2} I should see the spectra in their whole. A peak is a feature, not a spot where there is a (rel) maximum. For instance, these measurements should be have done in water. Water cut off is about 200 nm! $\endgroup$ – Alchimista Jul 21 '17 at 12:51
  • $\begingroup$ 3} depending on the size of the particles there can be a baseline shift due to scattering. This goes as inverse lambda^4 so get to max at the blu side of the window( 200 nm in your case, but it not a peak, see comment 1} $\endgroup$ – Alchimista Jul 21 '17 at 13:11

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