Non-monotonous size-dependent photoluminescence and excitonic relaxations in nanostructured ZnO thin films.

The size dependence of room-temperature photoluminescence (PL) accompanied with near-band-edge emission (NBE) and defect-associated green emission (GE) was investigated using high-quality crystalline nanostructured ZnO thin films with grain sizes varying from 29 nm to 2 nm. The size dependence of correlated intensities of the PL bands was pursued in correlation with structural and defect evolution revealed by X-ray photoelectron spectroscopy (XPS) and previous studies of XRD and Raman scattering. In contrast to the influence of thermally activated reconstruction and changes in defect densities, quantum size effects emerging at grain sizes below a critical value, , ∼ 10 nm were inspected in relation to the observed blueshift in the bandgap and correlated variations in the size dependence of the intensity of NBE and GE.

New Insights into the Role of Weak Electron⁻Phonon Coupling in Nanostructured ZnO Thin Films.

High-quality crystalline nanostructured ZnO thin films were grown on sapphire substrates by reactive sputtering. As-grown and post-annealed films (in air) with various grain sizes (2 to 29 nm) were investigated by scanning electron microscopy, X-ray diffraction, and Raman scattering. The electron⁻phonon coupling (EPC) strength, deduced from the ratio of the second- to the first-order Raman scattering intensity, diminished by reducing the ZnO grain size, which mainly relates to the Fröhlich interactions.