UV Photoluminescence Microscopy of Individual ZnO Nanostructured Clusters

Abstract

Ultraviolet (UV) photoluminescence (PL) spectra were acquired from individual nanostructured ZnO clusters less than 1 μm in size. The nanostructured clusters were formed by aggregation of a small number of nanoparticles. This analysis employed a microscopy apparatus specially designed for PL assessments of nanostructures at UV wavelengths with a spatial resolution of 0.395 μm. Atomic force microscopy was also employed to ascertain the sizes and morphologies of the nanostructured clusters. The ZnO samples were prepared by laser ablation in liquid (LAL) and comprised spherical, rhomboid, or gel-coated particles. PL emissions originating from free excitons (FX), FX phonon replicas, and defects were observed. The FX peak widths and positions were found to vary (with positions from 3.30 to 3.36 eV), suggesting that a range of particle sizes and morphologies was obtained from the LAL process. FX peaks at higher energies exhibited greater widths as a consequence of a quantum size effect originating from the crystallites comprising the nanostructured clusters. The rhomboid particles showed less-intense emissions related to defects compared with the other two types while also exhibiting the least intense emissions related to FX phonon replicas. This work also examined the mechanism by which nanoparticles were produced by LAL on the basis of the spectroscopic data. The information presented herein is expected to assist in the design and fabrication of semiconductor nanoparticles for future nanotechnology applications.