The
photoluminescence (PL) and reflectivity characteristics of zinc oxide
nanopillars (ZnO-NPs) grown on indium–tin–oxide (ITO)-coated
glasses were investigated. The room temperature PL showed bright white-light
emission for the undoped ZnO-NPs grown at 600 °C, suggesting
the close relation between the optical characteristic and the growth
conditions being carried out for obtaining the present ZnO-NPs. The
reflectivity of the as-grown ZnO-NPs array was about ∼29% with
the wavelength of the incident light ranging from 200 to 1800 nm.
Nevertheless, the reflectance reduced significantly to less than 9.9%
when a layer of gold (Au) was deposited on ZnO-NPs by sputtering for
5 min, corresponding to more than 65% reduction in Au-coated ZnO-NPs
(Au/ZnO-NPs). Moreover, the angle-resolved reflectance measurements
on the present Au/ZnO-NPs array show an omnidirectional light-trapping
characteristic. These remarkable characteristics, broadband and omnidirectional
light-trapping of Au/ZnO-NPs, are attributed to the extended effective
optical path of the incident light due to subwavelength scattering
resulting from the presence of Au nanoparticles.