Two-Photon Photoluminescence from Hierarchical ZnO Nanostructures

Hierarchical ZnO nanostructures (such as nanowires, nanocombs and nanohedgehogs) were grown by means of a vapor-phase transport technique in a tubular furnace. Silicon based substrates were used, over which Au nanoclusters were deposited as growth catalyzers. We study the two-photon absorption induced photoluminescence (TPPL) from the various ZnO nanoobjects grown using a micrometer sized polarised laser beam as the excitation source. The UV region of the TPPL spectra contains various peaks whose different patterns depend on the type of nanostructure and its orientation with respect to the incident polarization. We identify the peaks in the TPPL spectra, which are found to be dominated by free exciton emission and their phonon replicas. For the nanocomb, however, Fabry-Perot modes originating from optical multiple reflections within the comb's teeth are demonstrated.