Nanowire lasers are versatile light emitters that may be used in high performance optoelectronic devices at the nanoscale. Researchers from the Institute of Chemistry at the Chinese Academy of Sciences have now realized nanowire waveguides and lasers made from crystals of 2,4,5-triphenylimidazole (TPI)—a small organic molecule.

Compared to lasers made from inorganic semiconductors, organic materials offer several intrinsic advantages such as ease of fabrication, high fluorescence efficiency and superior control over the wavelength of light emitted by careful design of the molecules. In addition, the fabrication of nanowire structures of similar size as the wavelength of the emitted light offers strong control over the light emission as well as the guiding of light through the structure. To this end, nanowire lasers made from amorphous polymers have been demonstrated recently.

Here, the researchers instead use crystalline nanowires made from a small molecule, TPI. “The important advantage of small molecules is the ease with which crystals can be grown,” says Yong Sheng Zhao, a member of the research team. “Compared to amorphous structures, crystals offer a much better electronic and optical properties.”

Fig. 1: A photoluminescence microscope image of the emission of purple-ultraviolet light from TPI nanowires.

In this report, Yong Sheng Zhao, JiannianYao and colleagues describe the photonic properties of TPI nanowires.1 In particular, the nanowires were used as waveguides for propagation of light at 375 nm, in the purple-ultraviolet part of the spectrum (Fig. 1). Light not only passes very efficiently through these wires, but at sufficient excitation by an external pump laser, the nanowires start to emit laser radiation. This laser emission is strongly dependent on length and width of the nanowires because if the nanowires are either too short or too narrow then lasing modes cannot be sustained along the nanowire and optical emission is suppressed.

However, the achievement of laser emission is only a first step towards the functionalisation of these structures in integrated photonic devices, as for example the demonstration of an electrically excited laser remains. As Zhao emphasizes, “the research in nanomaterials based on small organic molecules is still in its infancy.” Nevertheless, the lasing from nanowires of TPI shows potential for nanophotonics based on organic molecules.