I am searching information about a possible Raman mode of ZnO at about 75 cm-1 (perhaps active after damaging/disorder induced by irradiation?..). Does someone knows about TA(A)/TO(A) ZnO phonons? I have found something not exhaustive in:
PHONON DISPERSION IN ZnO, W. WEGENER and S. HAUTECLER, Phys. Lett. 1970 vol.31A, n. 1
Optical spectroscopy of 3d and 3d impurity configurations in a wide-gap semiconductor (Zno:Co, Ni, Cu), H.-J. Schulz and M. Thiede, Phys Rev. B (1987) vol. 35, n. 1
Thank you very much! Actually we have found the peak after FIB irradiation, so may be you are right about the attribution to the presente of ZnO nanoparticles..