Low-threshold nanoscale lasers are attractive for their promising applications in highly integrated photonic devices and systems. Here we report the controllable growth of composition-symmetric CdS x Se 1−x nanowires by using a multistep thermal evaporation route with moving sources. Microstructure analyses reveal the obtained wires are highquality single crystals with the composition gradually changed from the center toward their both ends. Under laser illumination, these wires exhibit symmetrical color distribution along the length direction, with red at the center and green at the both ends. Optically pumped lasing is realized at room temperature using these composition-symmetric nanowires, with the threshold several times lower than that of compositionhomogeneous wires. This new nanowire structure will have potential applications as low-threshold nanoscale lasers in integrated nanophotonics.

The optical-transport properties of 1D Se-doped CdS nanostructures with different doping contents and/or crystallization degrees are reported. The locally excited photoluminescence shows a significant redshift during the transport along the long axis of the 1D structures and can leave enough PL intensity for detection. The magnitude of the redshift is found to be highly dependent on the content of doping and the crystallization degree. The experimental results are compared with theoretical calculations based on the fundamental absorption rule of the semiconductor, which demonstrates that the redshift is related to the optical reabsorption effects induced by the local structural disorder in the semiconductors. Such optical properties of 1D semiconductor structures might be of interest for potential applications in color-tunable nanosized light-emitting and/or frequency-converting devices.

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