We report the realization of a low-temperature aqueous pathway for the chemical synthesis of zinc oxide (ZnO) nanowires with low defect density and their room-temperature ultraviolet lasing behavior at low pump fluence. The concentration of solutes determined not only the size of individual nanowires, which influences their optical waveguiding behavior, but also their lattice defect density, which affects the efficiency of ultraviolet emission. The optimal synthesis conditions led to low-temperature growth of ZnO nanowires that showed room-temperature ultraviolet lasing at a low threshold of pump fluence. Based on our experimental results and optical waveguide theory, we report two important factors for realizing high-quality ZnO nanowires that show room-temperature ultraviolet lasing via a low-temperature aqueous approach: control of the density of defects generated in aqueous solutions and the optimal microstructure of the grown nanowires to produce strong optical confinement.

ZnO nanopillar arrays with high aspect ratios, such as the one shown in the figure, are fabricated from aqueous solutions at low temperatures using a polymer mold. The shape and dimensions of the nanopillars can be tuned by appropriately patterning the polymer mold. A hexagonal ZnO nanopillar array shows photonic bandgaps at visible wavelengths, as predicted by photonic band structure calculations.