UV Photoluminescence Microscopy of Individual ZnO Nanostructured Clusters

Ultraviolet (UV) photoluminescence(PL) spectra were acquired fromindividual nanostructured ZnO clusters less than 1 & mu;m in size.The nanostructured clusters were formed by aggregation of a smallnumber of nanoparticles. This analysis employed a microscopy apparatusspecially designed for PL assessments of nanostructures at UV wavelengthswith a spatial resolution of 0.395 & mu;m. Atomic force microscopywas also employed to ascertain the sizes and morphologies of the nanostructuredclusters. 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 foundto vary (with positions from 3.30 to 3.36 eV), suggesting that a rangeof particle sizes and morphologies was obtained from the LAL process.FX peaks at higher energies exhibited greater widths as a consequenceof a quantum size effect originating from the crystallites comprisingthe nanostructured clusters. The rhomboid particles showed less-intenseemissions related to defects compared with the other two types whilealso exhibiting the least intense emissions related to FX phonon replicas.This work also examined the mechanism by which nanoparticles wereproduced by LAL on the basis of the spectroscopic data. The informationpresented herein is expected to assist in the design and fabricationof semiconductor nanoparticles for future nanotechnology applications.