Optical Properties of Oxide Nanostructures
Zinc oxide, ZnO, is a wide band-gap semiconductor with a wide range of possible applications including blue/ultraviolet (UV) optoelectronic devices and piezoelectric devices. The large ZnO exciton binding energy of 60 mV makes this material an attractive candidate for room-temperature lasing, and low dimensional nanostructured ZnO offers the possibility of further improving lasing conditions due to quantum confinement effects.
We have investigated morphological control over photoluminescence of ZnO nanorods by thermal decomposition of zinc acetate in organic solvents in the presence of oleic acid, which produces relatively monodisperse ZnO nanorods (ZnO quantum rods) with diameters of 2 nm and lengths in the range 40-50 nm. The diameter, an order of magnitude smaller than previously reported, shows strong evidence of quantum confinement when compared to bulk crystalline ZnO optical properties. Our recent progress in the synthesis of transition metal oxide nanocrystals prompted our experiments to prepare nanoscale ZnO.
The intensity of the green band emission, common to many ZnO structures, was found to vary with morphology (see rightt). Such behavior can be equated with surface oxygen vacancies, but further understanding of the physics can be advanced by continually driving for rational design approaches to ZnO, and extending the survey to doped structures (e.g. Mn doped ZnO).
The strongest green band intensity corresponds to the shape with the largest surface/volume ratio, attributed to surface oxygen vacancies.