Ultralong Homogeneously Alloyed CdSe_xS_1-x Nanowires with Highly Polarized and Color-Tunable Emissions

Colloidal semiconductor nanowires are attractive materials with polarized light absorption and emissions. Solution synthesis of ultralong (several tens of micro-meters) colloidal CdSe_xS_1-x nanowires with homogeneously alloyed composition through a solution-liquid-solid (SLS) method are reported. By varying the ratio of Se/S, the optical band and their corresponding photoluminescence spectra of the CdSe_xS_1-x nanowires can be finely tuned from 508 nm (ca. 2.45 eV) to 628 nm (ca. 2.0 eV). In comparison with the low quantum yields of pure CdS and CdSe nanowires (less than 0.1%), alloyed CdSe_xS_1-x nanowires exhibit enhanced bright photoluminescence emission with a narrow spectral width of 25-31 nm and moderate quantum yields up to ca. 8.8%. Moreover, the randomly oriented ensembles on glass wafers show strong polarized emission with polarization values of ca. 0.6 due to the inherent larger aspect ratio. The combination of these characteristics in alloyed nanowires sets the basis for the spectroscopic study of 1D excitons, as well as the fabrication of nanowire-based polarized photonic and optoelectronic devices. Solution prepared ultralong alloyed CdSe_xS_1-x nanowires have uniform 1D shape and high photoluminescence (PL) quantum yields, as well as composition-dependent and spectrally narrow polarized emission peaks tunable from 508 to 628 nm. Such properties can primarily benefit from the use of colloidal nano-wires as outstanding luminescent materials for saturated full-color polarized photonic and optoelectronic devices.