Emission wavelength selection via anomalous polarized fluorescence in ZnO-C nanowires

Defect fluorescence from high aspect ratio semiconductor nanowires typically displays a weak polarization parallel to the nanowire’s long axis due to dielectric mismatch in high aspect ratio media. Instead, anomalous 2.2 eV defect fluorescence distinctly polarized perpendicular to the nanowire is observed and measured from carbon-incorporated zinc oxide nanowires. These observations are significant because polarized defect emissions with consistent polarization on a mesoscopic scale are uncommon. Through a systematic study and comparison of experimental results with density functional theory calculations, an oriented defect complex comprising carbon substituting on an oxygen site and an oxygen vacancy (C_O-V_O) is deduced to be responsible for the anomalous yellow fluorescence, demonstrating a method for relating atomic-scale defect geometry to mesoscopic properties. The anomalous emission can appear in both green- and red-fluorescing nanowires grown with different carbon concentrations, verifying the independence and uniqueness of the 2.2 eV emission. This allows for polarization-dependent emission wavelength selection from a single nanowire.