Multicolored quantum dots enable white light applications

Carbon quantum dots, an environmentally friendly fluorescent material, are promising candidates for LEDs. However, fabricating solid state carbon quantum dots, or CQDs, that can emit white light is challenging. Chen et al. have overcome these issues by utilizing an old trick with different materials to create superior CQDs to emit white light.

The authors used the standard one-step hydrothermal fabrication process for creating CQDs. But by using different materials – 1,3-Dihydroxynaphthalene and hydrochloric acid – they were able to avoid the issue of agglomeration, which traditionally plagues solid-state CQD production and leads to a redshift of the emitted light. This method relied on the principle of solvent similarity compatibility, which can isolate the matrix material to avoid the agglomeration of CQDs in the process of forming a solid film.

“Our work provides reference and guidance for solving the agglomeration problem of other quantum dots,” said author Xifang Chen.

The CQDs were analyzed with spectroscopy and a transmission electron microscope. This revealed the luminescence of the CQDs stemmed from carbon-oxygen related surface fluorophores. They were also blue and green double band luminescent.

A solid-state white LED was made by embedding the CQDs in polymethyl methacrylate matrix. The resulting LED was able to produce a cold white light when excited by an ultraviolet LED chip. The results show the optical properties of CQDs can be maintained through the process of forming solid films, which opens doors for their use in LED applications.

Source: “Blue and green double band luminescent Carbon quantum dots: Synthesis, origin of photoluminescence, and application in white light-emitting devices,” by Xifang Chen, Wenhui Wu, Wenxia Zhang, Ziye Wang, Zhenjin Fu, Lei Zhou, Zao Yi, Gongfa Li, and Liangcai Zeng, Applied Physics Letters (2021). The article can be accessed at https://doi.org/10.1063/5.0046495 .