Chinese Scientists Develop Color Tunable Single Graphene-based LEDs

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A research team from Beijing Tsing Hua University has made a groundbreaking graphene LED that is capable of color tuning to most colors under the visible spectrum, according to a Phys.org report.

LEDs essentially are only able to emit one specific color. The chemical composition of the phosphor coating determines the color of LEDs, and it has been difficult for the industry to develop a single LED chip that is capable of changing various shades of colors. To achieve color tuning effects in LED products, manufacturers have been mixing different RGB LEDs.

However, the research team led by Professor Tian-Ling Ren from Beijing Tsing Hua University has resolved this issue by mixing graphene oxide (GO) with reduced graphene oxide (rGO).

By blending the two graphene properties, Ren’s team was able to create a series of discrete energy levels, which allows the emittance of many different colors. The graphene LEDs are capable of emitting colors within the visible spectrum range of 450nm to 750 nm, basically from blue to red.

Graphene is not known to be particularly luminescent material, due to the lack of a bandgap. The research team has been able to create a bandgap on the partially reduced interfacial GO by blending GO and rGO.

The blending process occurs in nanoclusters, where the rGO is reduced to different degrees at the interface and exhibit various energy levels of excitement, hence the color of light.

By mixing GO with the more refined rGO, a bandgap was created that allows electrons to jump across to conduct electricity or emit light.

The research team still needs to overcome lifetime and reliability issues before the graphene LED can be applied in commercial applications, such as lighting, backlight, and mobile devices.

Ren’s team has worked with 20 graphene LED prototypes, while the lights have demonstrated high brightness, the lights have very low efficiency. Another drawback is the lights have a very short emission lifetime of less than one minute in ambient conditions and two hours in a vacuum.

 

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