Manoj... The sharpness of the IR peaks is a very good and simple indication on the purity of the analyzed sample. If not sharp there exists some other material that has absorption in the vicinity of your signals. The sharper peaks mean purer sample. YOU are right.

Thank you Mahmood

No, I do not agree with you and Mahmood. Generally the sharpness does not directly relate with the purity. It is esentially the reflection of vibrational transition energy of a chemical bond. e.g., for the same group, the crystalline band is generally narrower than the amorphous. In addition, the added amounts of sample for preparing KBr disc will also affects the width of the band, i.e., too many samples may lead to the expansion of band width. For the band of protein, if amide I or II band is used for analysis, the wider band might also be caused by the mixing of several secondary structures, e.g. apha-helix, beta-sheet, beta-turn, or random coil.

FTIR technology is usually used to identify functional groups. The vibration spectrum of a molecule is considered to be a unique material property and molecule. In this way we can say that sharp peaks represent the correctness of the compound. You can be tested by comparing the recorded spectrum with the previously recorded reference spectrum.