A mixture of polymers and tiny crystals can be spun together into fibers that emit white light, Chinese researchers have found.1 Their research is part of a broader effort to develop materials that can replace conventional lighting or video display technologies with lower-cost, lower-power devices.

Certain semiconducting polymers can emit a range of colors in response to an electrical current or illumination with ultraviolet (UV) light. Adding nanocrystals can potentially make these materials easier to process into solids, improve their efficiency and also tune the color of the light they emit.

However, blending the components can be difficult. Polymers such as poly(p-phenylene-vinylene) (PPV) have been widely used to create these light-emitting semiconductors, but they are generally more soluble in organic solvents, which do not mix well with water-soluble nanocrystals. What’s more, the light-emitting properties of the liquid precursors are usually different from the solids they form, making it difficult to determine whether they will produce the desired color of light.

Haizhu Sun, Bai Yang and colleagues at Northeast Normal University and Jilin University in China, have instead turned to a precursor of PPV that is soluble in water. Mixing this with poly vinyl alcohol (PVA) and heating to 100 °C for three minutes produced a new polymer that glowed blue when irradiated with UV light. The team found that heating the mixture was a crucial step, as doing so formed chemical bonds that helped to almost double the light output of the material.

The scientists then added cadmium-tellurium (CdTe) nanocrystals to the mix, which on their own emit yellow light. PVA helped to tune the electrostatic interaction between the PPV precursor and the nanocrystals, stabilizing the nanocrystals and creating a liquid that emitted white light under UV. After adding a surfactant, this solution could be turned into fibers by a process called electrospinning, where a thin jet of liquid is stretched out by a high voltage.

Fig. 1: Sanning electron microscope image of white light-emitting nanofibers.

These fibers were 100–200 nanometers wide (Fig. 1), and produced a strong white light emission under UV. The scientists say that the process “is simple and easily scaled up.” They now plan to make white-light-emitting devices using the fibers.