Photoluminescence and multiphonon resonant Raman scattering in low-temperature grown ZnO nanostructures

The authors report on the optical properties of nanocrystalline ZnO grown at 200°C by radio-frequency magnetron sputtering. The nanocrystalline nature of the films was confirmed by cross-sectional transmission electron microscopy. In these films, ZnO nanocrystals with an average size of about 3–5nm were embedded in an amorphous matrix. The photoluminescence spectra from such nanostructured thin films show the near-band-edge emissions around 3.3eV. A redshift of about 8–11cm−1 is observed in the case of first-order longitudinal-optical (LO) phonon of ZnO in such nanostructures when compared to the LO phonon peak of bulk ZnO. The ultraviolet resonant Raman excitation at 77K shows multiphonon LO modes up to eighth order.

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