Researchers at the National University of Singapore (NUS) have developed a way to give a massive boost to the photoluminescent efficiency of tungsten diselenide. In so doing, they may have paved the way for this two-dimensional semiconductor—which belongs to a class of 2-D crystals known as transition metal dichalcogenides—to have a greater impact on optoelectronics and photonics, including applications such as photovoltaics, quantum dots, and LEDs.
While all of these applications take advantage of tungsten diselenide’s ability to convert light to electricity and vice versa, the material’s thinness is a limiting factor in its ability to absorb photons and its photoluminescence.
In research described in the journal Nature Communications, the NUS researchers turned to plasmonic nanostructures, which exploit oscillations in the density of electrons that are generated when photons hit a metal surface, to improve the brightness of tungsten diselenide’s photoluminescence by 20,000 times.
“This is the first work to demonstrate the use of gold plasmonic nanostructures to improve the photoluminescence of tungsten diselenide,” said Wang Zhuo, one of the NUS researchers and first author of the paper, in a press release. “We have managed to achieve an unprecedented enhancement of the light absorption and emission efficiency of this nanomaterial.”
Prior attempts at improving the photoluminescence of tungsten diselenid—which involved simultaneously improving its absorption, emission and directionality—managed to make it shine only 1,000 times as bright as it does in its natural state.
The NUS researchers achieved the 20,000-fold brightness increase by suspending flakes of tungsten diselenide over sub-20-nanometer-wide trenches in a gold substrate. The researchers say this design yields such a huge increase due to enhanced absorption of the photons emitted by the pump laser. The absorption boost, they concluded, is because of plasmons that are confined in the trenches.
“The key to this work is the design of the gold plasmonic nanoarray templates,” said Andrew Wee, a professor at NUS, in the press release. “In our system, the resonances can be tuned to be matched with the pump laser wavelength by varying the pitch of the structures. This is critical for plasmon coupling with light to achieve optimal field confinement.”
In continuing research, the NUS team will examine how effective the gold plasmons are in enhancing electroluminescence of transition metal dichalcogenides. They intend to extend this investigation into a range of 2-D transition metal dichalcogenides with different band gaps. The researchers expect that each one will employ different interaction mechanisms.