The crystallite size can certainly affect the phonon interactions in the system, and one may expect the Raman linewidth associated with the molecules of a given sample to differ in crystalline and polycrystalline forms.
1. Is it possible that the Raman width for both cases could be same
2. Could it happen for a polycrystalline sample to acquire narrower peaks (less Raman width) than its single crystal counterpart.
FWHM of Raman peaks for polycrystalline samples should be larger than the corresponding single crystals of identical composition, almost always. An opposite trend will be exceptional or extremely rare. Other than that, single crystal peaks will almost resemble a symmetric Lorentzian function, while polycrystalline samples or nanostructures or systems with defects will possess a certain level of Fano asymmetry.
Hi Souvik Bhattacharjee
Thanks for your answer.
Could you please share some information about the rare "opposite trend".
Suppose, in a polycrystalline sample whose grain size is quite large that it covers the probing laser spot so that the measurement confines to only that particular crystallite. Then, do u believe that it may resemble with its single crystal counterpart, or still there may exist some factors.
Dear Omkar Rambadey,
Look over the data below:
https://www.spectroscopyonline.com/view/why-are-raman-spectra-crystalline-and-amorphous-solids-different
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Why are the Raman spectra of crystalline and amorphous solids different?
The Raman spectra of crystalline and amorphous solids of the same chemical composition can be significantly different primarily because of the presence or absence of spatial order and long-range translational symmetry, respectively.
Which of the followings can be identified from crystal structure using Raman spectra?
Crystal structures and chemical compositions were determined by single crystal X-ray diffraction (XRD) analysis and confirmed by XRD of powders and elemental analysis. Raman spectroscopy of new crystals evidences the presence in crystals of MBI-, H3PO3-, or H3PO4- and water molecules.
Theory of the resonance Raman effect in crystals R. Loudo
https://hal.archives-ouvertes.fr/jpa-00206334/document
Omkar Rambadey If the grains or crystallites are quite large, and there is almost no disorder or defect in the system, then the FWHM might be as low as of the single crystal. I have not experienced the opposite case for any material yet.
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