Defect induced variation in vibrational and optoelectronic properties of nanocrystalline ZnO powders

Structural disorder of ZnO nanopowders with mean crystallite size down to 15 nm, produced by mechanical activation in high energy mills, has been analyzed by x-ray diffraction and Raman spectroscopy. The influence of such disorder on optical and electronic properties of activated ZnO nanopowders has been investigated using photoluminescence spectroscopy and spectroscopic ellipsometry. A revised interpretation of the resonant enhancement of the first and second order Raman scattering by the E1(LO) phonons in highly disorder ZnO nanopowders has been proposed. Detailed analysis of resonant Raman effects in ZnO powders under sub band gap excitation has given valuable information about defect induced electronic states in the band gap of ZnO. Systematic trend in the electron–phonon coupling strength, with the correlation length which depends on lattice disorder in ZnO, has been also demonstrated.