Hello Peter, I am well aware withe the question putted by you. Peaks in PL excitation spectra represents the absorption line of the material. But I am failing to understand that why we choose a constant emission wavelength while recording PL excitation spectra  

Dear Peter, as I understand excitation spectra is a kind of absorption spectra of the material where we impinge a range of energy on our sample and simply record the characteristic absorption line. As i understand, this process resembles with UV-Vis absorption spectroscopy, where we don't need to set any emission wavelength to record the absorption spectra of the material of interest. So please clarify my doubt as soon as soon as possible. Any suggested literature is also appreciated in advance.

Thanks Peter.