Quantum dots help create light-emitting metasurfaces

A team of researchers from the Pohang University of Science and Technology (POSTECH) have used Nanoimprint Lithography (NIL) to fabricate metasurfaces embedded with quantum dots, enhancing their luminescent efficiency. Their research findings have been published in the journal Nano Letters.

NIL, a process for creating optical metasurfaces, utilises patterned stamps to quickly transfer intricate patterns at the nanometre (nm) scale. This method offers cost advantages over electron beam lithography and other processes; it also enables the creation of metasurfaces using materials that are not available in conventional processes.

Metasurfaces have become the focus of extensive research for their ability to control the polarisation and emission direction of light from quantum dots. Quantum dots, which are nanoscale semiconductor particles, are efficient light emitters capable of emitting light at precise wavelengths. They are widely used in applications such as QLEDs and quantum computing. However, conventional processes cannot embed quantum dots within metasurfaces. As a result, research has often involved fabricating metasurfaces and quantum dots separately and then combining them, which imposes limitations on controlling the luminescence of the quantum dots.

In this study, the researchers integrated quantum dots with titanium dioxide (TiO2), a material used in the NIL process, to create a metasurface. Unlike conventional methods, which involve separately fabricating the metasurface and quantum dots before combining them, this approach embeds the quantum dots directly within the metasurface during its creation.

The resulting metasurface enhances the proportion of photons emitted from the quantum dots that couple with the resonance mode of the metasurface. This advancement allows for more effective control over the specific direction of light emitted from the quantum dots compared to previous methods. Experiments demonstrated that the more photons emitted from the quantum dots that were coupled to the resonant modes of the metasurface, the higher the luminescence efficiency. The researchers’ metasurface reportedly achieved up to 25 times greater luminescence efficiency compared to a simple coating of quantum dots.

Professor Junsuk Rho, who led the research, said the use of luminescence-controlled metasurfaces will enable sharper, brighter displays and more precise, sensitive biosensing. “Further research will allow us to control luminescence more effectively, leading to advances in areas such as nano-optical sensors, optoelectronic devices and quantum dot displays,” Rho said.

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