New Light Source Uses Solid Fog

Aerobornitride scatters the light of a laser beam homogeneously in all directions. (Source: F. Rasch)

With a porosity of 99.99 %, it consists prac­tically only of air, making it one of the lightest materials in the world: Aero­bornitride is the name of the material developed by an inter­national research team led by Kiel University. The scientists assume that they have thereby created a central basis for bringing laser light into a broad appli­cation range. Based on a boron-nitrogen compound, they developed a special three-dimensional nano­structure that scatters light very strongly and hardly absorbs it. Irra­diated with a laser, the material emits uniform lighting, which, depending on the type of laser, is much more effi­cient and powerful than LED light. Thus, lamps for car headlights, projectors or room lighting with laser light could become smaller and brighter in the future. The project is part of the Europe-wide research ini­tiative Graphene Flagship, which involves a total amount of around 150 research groups from science and industry in 23 countries.

In research and industry, laser light has long been considered the next gene­ration of light sources that could even exceed the efficiency of LEDs. “For very bright or a lot of light, you need a large number of LEDs and thus space. But the same amount of light could also be obtained with a single laser diode that is one-thousandth smaller,” Fabian Schütt empha­sizes the potential. His working group “Functional Nano­materials” at Kiel University colla­borates with other researchers from Germany, England, Italy, Denmark and South Korea.

Powerful small light sources allow numerous appli­cations. The first test appli­cations, such as in car headlights, are already available, but laser lamps have not yet become widely accepted. On the one hand, this is due to the intense, directed light of the laser diodes. On the other hand, the light consists of only one wavelength, so it is mono­chromatic. This leads to an unpleasant flickering when a laser beam hits a surface and is reflected there.

“Previous develop­ments to laser light normally work with phosphors. However, they produce a relatively cold light, are not stable in the long term and are not very efficient,” says Rainer Adelung, head of the working group. The research team in Kiel is taking a different approach: They developed a highly scattering nano­structure of hexagonal boron nitride, also known as white graphene, which absorbs almost no light. The structure consists of a filigree network of countless fine hollow microtubes. When a laser beam hits these, it is extremely scattered inside the network structure, creating a homo­geneous light source. “Our material acts more or less like an arti­ficial fog that produces a uniform, pleasant light output,” explains Schütt. The strong scattering also contri­butes to the fact that the disturbing flickering is no longer visible to the human eye.

The nano­structure not only ensures that the material withstands the intense laser light, but can also scatter different wavelengths. Red, green and blue laser light can be mixed in order to create specific color effects in addition to normal white – for example, for use in inno­vative room lighting. Here, extremely light­weight laser diodes could lead to completely new design concepts in the future. “However, in order to compete with LEDs in the future, the effi­ciency of laser diodes must be improved as well,” says Schütt. The research team is now looking for industrial partners to take the step from the labora­tory to appli­cation.

Meanwhile the researchers from Kiel can use their method to develop highly porous nano­structures for different materials, besides boron nitride also graphene or graphite. In this way, more and more new, light­weight materials, aero­materials, are created, which allow parti­cularly innovative appli­cations. For example, the scientists are currently doing research in colla­boration with companies and other univer­sities to develop self-cleaning air filters for aircraft. (Source: U. Kiel)

Reference: F. Schütt et al.: Conversionless efficient and broadband laser light diffusers for high brightness illumination applications, Nat. Commun. 11, 1437 (2020); DOI: 10.1038/s41467-020-14875-z

Link: EU-initiative Graphene-Flagship, Brussels, Belgium Functional Nanomaterials, Institute for Materials Science, Kiel University, Kiel, Germany

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