The band observed at 1520 cm 1 is due to the presence of C@O vibrations [22]. The weak absorption bands in the region of 900–1100 cm 1 are an indication of CAH stretching vibrations. In general, hydrogen in oxide crystals prefers to chemical ly form strong OH bonds with lattice O. In ZnO, theoretical, first-principles calculations and experimental studies revealed that hydrogen usually forms strong bonds with lattice O and the stretching vibrational modes of OH bonds are responsible for the IR absorption peaks observed . In this study, a broad band was observed in the region of 3690 cm 1 which can be explained as overlapping OAH and CAH stretching modes [45].