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Scientists Develop Novel Non-toxic Light Emitting Nanoparticles

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Osaka researchers create nanoparticle from ternary non-toxic semiconductors to help create displays and LED lighting with better colours

Most current displays do not always accurately represent the world's colours as we perceive them by eye, instead only representing roughly 70 percent of them. To make better displays with true colours commonly available, researchers have focused their efforts on light-emitting nanoparticles.

Such nanoparticles can also be used in medical research to light up and keep track of drugs when developing and testing new medicines in the body. However, the metal these light-emitting nanoparticles are based on, namely cadmium, is highly toxic, which limits its applications.

So far researchers have succeeded in creating non-toxic nanoparticles that emit light in an efficient manner by creating semiconductors with three types of elements in them, for example, silver, indium, and sulphur (in the form of silver indium disulphide (AgInS2)). However, the colours they emit are not pure enough--and many researchers declared that it would be impossible for such nanoparticles to ever emit pure colours.

Now, researchers from Osaka University have proven that it is possible by fabricating semiconductor nanoparticles containing AgInS2 and adding a shell around them consisting of a semiconductor material made of gallium and sulphur. The team was able to reproducibly create these shell-covered nanoparticles that are both energy efficient and emit vivid, clean colours. The team have recently published their research in the Nature journal NPG Asia Materials.

"We synthesised non-toxic nanoparticles in the normal way: mix all ingredients together and heat them up. The results were not fantastic, but by tweaking the synthesis conditions and modifying the nanoparticle cores and the shells we enclosed them in, we were able to achieve fantastic efficiencies and very pure colours," study coauthor Susumu Kuwabata says.

Enclosing nanoparticles in semiconductor shells in nothing new, but the shells that are currently used have rigidly arranged atoms inside them, whereas the new particles are made of a more chaotic material without such a rigid structure.

"The silver indium disulphide particles emitted purer colours after the coating with gallium sulphide. On top of that, the shell parts in microscopic images were totally amorphous. We think the less rigid nature of the shell material played an important part in that--it was more adaptable and therefore able to take on more energetically favorable conformations," first author Taro Uematsu says.

The team's results demonstrate that it is possible to create cadmium-free, non-toxic nanoparticles with very good colour-emitting properties by using amorphous shells around the nanoparticle cores.

'Narrow band-edge photoluminescence from AgInS2 semiconductor nanoparticles by the formation of amorphous III-VI semiconductor shells' was published in NPG Asia Materials, https://doi.org/10.1038/s41427-018-0067-9.

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