Fluorescence and infrared spectroscopy of electrochemically self assembled ZnO nanowires: evidence of the quantum confined Stark effect

We report room temperature fluorescence (FL) and infrared absorption (IR) spectra of spatially ordered two-dimensional arrays of vertically standing ZnO nanowires. The wires are produced by selective electrodeposition of Zn in 10-, 25- and 50-nm pores of a porous anodic alumina film, followed by chemical oxidation. Wires of different diameters show distinctly different FL emission characteristics associated with either deep level traps, or exciton recombination. The intensity of the peak caused by exciton recombination is larger than that caused by deep level traps, which is unusual in nanostructures, and attests to the high structural purity. We also see an anomalous red-shift in the FL emission spectrum which appears to be evidence of quantum confined Stark shift caused by built-in electric fields in the alumina template. The IR absorption spectra are mostly featureless and show no significant peaks indicating the absence of shallow level traps.