The low-frequency optical and dielectric properties of ZnO tetrapod structures prepared by thermophysical method were studied by terahertz time-domain spectroscopy. The power absorption, refractive index, and the complex dielectric function were measured in the frequency range from 0.2to3.5THz. Based on a simple effective medium theory, the low-frequency dielectric properties of ZnO tetrapods were found to be associated with the transverse optical E1 phonon mode, which is consistent with that observed in bulk single-crystal ZnO.

Far-infrared optical and dielectric properties of nanostructured ZnO of different morphologies are characterized by terahertz time-domain spectroscopy. Frequency-dependent complex dielectric function, power absorption, and refractive index are experimentally measured in the terahertz regime. The results are analyzed and well fit with dielectric theories combined with effective medium models. Different ZnO nanostructure morphologies exhibit different characteristics due to diverse resonance mechanisms dominated by either free electrons or phonons. The dielectric function of tubular and prismlike ZnO structures exhibits the Drude-like behavior, while it is dominated by the low-frequency phonon resonances for nanowires. Additionally, the overall lowfrequency phonon resonances of these nanostructures are measured by Raman scattering spectroscopy, showing good consistency with those of bulk wurtzite single-crystal ZnO.

X-ray absorption near-edge structure ͑XANES͒, extended x-ray absorption fine structures ͑EXAFS͒, and photoluminescence measurements were used to elucidate the microstructural and photoluminescence properties of ZnO nanowires ͑ZnO-NWs͒ that had been treated with Eu by thermal diffusion. The O K-and Eu L 3-edge XANES and EXAFS spectra at the Zn K-and Eu L 3-edge verified the formation of Eu 2 O 3-like layer on the surface of ZnO-NWs. X-ray diffraction, XANES and EXAFS measurements consistently suggest the lack of substitutional doping of Eu ions at the Zn ion sites in the interior of ZnO-NWs. The clear sharp and intense emission bands in the range 610-630 nm of Eu-treated ZnO-NWs originated from the intra-4f transition of Eu ions in the Eu 2 O 3-like surface layer.