On the influence of Raman scattering of water in the photoluminescence measurement of water dispersed ZnO nanocrystals.

We present our investigation on the photoluminescence properties of water dispersed ZnO nanocrystals at various excitation wavelengths, and show that one peak in the emission spectrum (recorded by spectrofluorometer) changes its position when the excitation wavelength is changed. The relationship between the peak position and the excitation wavelength is found to be linear. Recording of the emission spectra (by spectrofluorometer) of water at different excitation wavelengths reveals that the linearly varying peak is present in them as well. It could be recognized that the excitation wavelength dependent peak originates because of Raman scattering of water and it is not intrinsically related to the ZnO nanocrystals. The present work thus highlights the importance of considering Raman scattering of water while interpreting the emission spectrum (recorded by spectrofluorometer) of water dispersed ZnO nanocrystals, which otherwise may lead to misinterpretation such as UV emission and violation of the Kasha's rule, which actually may not be the case.