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Creating custom light using 2D materials:

Finding new semi-conductor materials that emit light is essential for developing a wide range of electronic devices. But making artificial structures that emit light tailored to our specific needs is an even more attractive proposition. However, light emission in a semi-conductor only occurs when certain conditions are met. Today, researchers from the University of Geneva (UNIGE), Switzerland, in collaboration with the University of Manchester, have discovered an entire class of two-dimensional materials that are the thickness of one or a few atoms. When combined together, these atomically thin crystals are capable of forming structures that emit customisable light in the desired colour. This research, published in the journal Nature Materials, marks an important step towards the future industrialisation of two-dimensional materials.

[...] "Our objective was to manage to combine different two-dimensional materials to emit light while being free from all constraints," continues professor Morpurgo. The physicists thought that, if they could find a class of materials where the velocity of the electrons before and after the change in energy level was zero, it would be an ideal scenario which would always meet the conditions for light emission, regardless of the details of the crystal lattices and their relative orientation.

A large number of known two-dimensional semi-conductors have a zero-electron velocity in the relevant energy levels. Thanks to this diversity of compounds, many different materials can be combined, and each combination is a new artificial semi-conductor emitting light of a specific colour. "Once we had the idea, it was easy to find the materials to use to implement it," adds professor Vladimir Fal'ko from the University of Manchester. Materials that were used in the research included various transition metal dichalcogenides (such as MoS2, MoSe2 and WS2) and InSe. Other possible materials have been identified and will be useful for widening the range of colours of the light emitted by these new artificial semi-conductors.

"The great advantage of these 2D materials, thanks to the fact that there are no more preconditions for the emission of light, is that they provide new strategies for manipulating the light as we see fit, with the energy and colour that we want to have," continues Ubrig. This means it is possible to devise future applications on an industrial level, since the emitted light is robust and there is no longer any need to worry about the alignment of atoms.

Nicolas Ubrig, et. al. Design of van der Waals interfaces for broad-spectrum optoelectronics. Nature Materials, 2020; DOI: 10.1038/s41563-019-0601-3

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