According to my knowledge, I knew that by varying the sample concentration one can vary the intensity of the PL emission, but in my sample, the PL emission wavelength keeps varying by changing the concentration of the sample. I would like to know if anyone has come across such kind of situations?
The emission wavelength should not vary with the concentration. If this is observed, there are two potential reasons: i) at high concentrations, you can get innerfilter and reabsorption effects. This means that the emitted photons are reabsorbed by a neighbouring species. In this case, PL becomes asymmetric (because the tail where the material absorbs light is swallowed) and looks red-shifted. ii) superstructures could be formed or electrons are screened differently due to changes in the environment which could also be induced by different concentrations. This can lead to broadening and red-shift or (less likely) narrowing and blue-shift. The peak should still remain symmetric in this case. Effect i) is very common and likely the case.
The emission wavelength should not vary with the concentration. If this is observed, there are two potential reasons: i) at high concentrations, you can get innerfilter and reabsorption effects. This means that the emitted photons are reabsorbed by a neighbouring species. In this case, PL becomes asymmetric (because the tail where the material absorbs light is swallowed) and looks red-shifted. ii) superstructures could be formed or electrons are screened differently due to changes in the environment which could also be induced by different concentrations. This can lead to broadening and red-shift or (less likely) narrowing and blue-shift. The peak should still remain symmetric in this case. Effect i) is very common and likely the case.
In the literature known concentration of the PL wavelength shifts.
Agree with Claudia Backes: for instance, in the attached paper authors said, that the concentration-dependent red-shift of the ZnO-NP emission peak was attributed to the self-absorption (fig.4a).
Article Characterization of optical properties of ZnO nanoparticles ...
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