In the article "Cr doping induced structural, phonon and excitonic properties of ZnO nanoparticles" ( https://link.springer.com/article/10.1007/s11051-011-0647-x ) I can see the following phrase:
"there is a broad band around 2.2 eV. These peaks are usually attributed to oxygen vacancies, surface dangling bonds and zinc interstitials. Doping of Cr shows no change in the 2.2 eV band, indicates it is not altering the surface
defects or surface dangling bonds"
But on the related figure that shows photoluminescence spectra, I can see that the extent of doping does not change position of 2,2 eV peak, but it significantly changes its height. Doesn't it show that Cr doping affects the dangling bonds and interstitials?
I don't know the exact answer... In PL spectra in solution or solid state whatever it is If you want to see any change of PL spectral shifts in your doped materials either it might be a blue shift (lower wavelength) or red shift (higher wavelength).But You only said that after doping no changes in peak 2.2 eV. This means no changes in PL spectra...But changes in height (that is PL intensity). It may be a higher concentration of ur doped materials....due to increase in height...
Change in the intensity of peak in the PL spectra generally refers to the difference in the concentration of the material in the solvent. If the concentration is more, more will be the peak intensity and vice-versa. Only shift in the peak position depicts the change in the PL spectra.
The vertical axis is expressed in "arbitrary units", maybe this is the source of your problem. First, it is not clear whether those units are identical for both curves - probably not. Maybe, even the position of zero signal is not the same (sometimes two curves are presented after some vertical shift to make their otherwise overlapping features better visible). Assuming that the origins are identical, all we can sensibly discuss is the location of extrema and the ratios of peaks' heights.
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