Lamps almost out of thin air

When thinking of laser light, the intense beam of a laser pointer probably springs to mind, rather than cosy living room lighting. But that is exactly what a project from materials science and inorganic chemistry is investigating: pleasant laser light.

For several years now, energy-saving light bulbs with light-emitting diodes (LEDs) have become the new lighting standard, and have displaced conventional light bulbs. But research and industry have already identified a next generation of light sources: laser light bulbs. "The problem with the current LEDs is their brightness," said Dr Fabian Schütt, who researches highly-porous nanomaterials. Very bright light requires a large number of LEDs, and thus a lot of space. The 31-year-old is convinced that "the same amount of light can be obtained with laser diodes, which are around one thousandth of the size." This would enable light bulbs for car headlights, projectors or ambient lighting to be smaller, lighter, and brighter at the same time. But so far, the intensive, monochromatic (unicolour) light beam of the laser has proven to be a problem for such applications. It causes flickering on surfaces and is usually considered to be unpleasant.

Schütt's solution approach is called "Aerobornitride": in the framework of "Graphene Flagship", the biggest ever research initiative in the European Union, he developed this extremely porous material, which consists almost entirely of air, and is thus one of the lightest materials in the world. It is made from an intricate network of countless hollow tubes, with a diameter of around 100 to 3,000 nanometres. If a laser beam hits this finely-branched structure, it is scattered so widely that a uniformly bright light source is created. "Our material works almost like artificial fog," explained Schütt. Different wavelengths of light – red, blue or green – are scattered by the special nanostructure, and thereby mix white and other colours.

After Schütt published his approach in a renowned scientific journal, and the story was covered by specialist publications, he received numerous enquiries from industry. But there is still a need for optimisation. "The efficiency of the green laser light is not yet up to the standard of the blue or red," said the materials scientist.

He is hoping for help from chemical engineer Huayna Terraschke, assistant professor of photoactive inorganic nanomaterials. Both are members of the priority research area Kiel Nano, Surface and Interface Science (KiNSIS) at the CAU. At a large workshop, they recognised areas of overlap between their work. Terraschke and her working group are specialised in "live" observation and testing of chemical reactions. The findings help them to develop photoactive nanomaterials. "These materials react to light or change their colour, and can be used for example in sensors, solar cells and light-emitting diodes," said the 35-year-old. For the project with Schütt, she created luminescent materials which can convert light, for example from blue to green. Green laser light can thus be produced artificially "indirectly", and can be specifically optimised when doing so. "My work is actually very specific fundamental research. It is exciting to also be able to develop solutions for specific applications, through a multidisciplinary project," said Terraschke about the collaboration.

With their joint project, Schütt successfully applied for funding through a KiNSIS support programme for young scientists. With these funds, they hired a student assistant for the chemical work in the laboratory. "The funding gives us the possibility to try out new avenues that we otherwise might not have pursued," said Schütt. Because they can’t yet say conclusively whether or not the plan to improve the concept using Terraschke’s luminescent materials will really work. But this is also part of science: the risk that a completely new approach doesn’t work. However, if the results are promising, this could be the beginning of the next, even bigger research project.

Author: Julia Siekmann