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Cluster glass shows promise to be a new, cleaner source of white light

18 Aug 2022

Discovery by German consortium of Gießen, Marburg and Karlsruhe universities relied on Stuttgart’s High Performance Computing Center.

Researchers in Germany have discovered “cluster glass”, a new class of materials, which, they say, shows promise for replacing white light sources such as LEDs.

The scientists comment that white light generation by relatively modern technologies such as LEDs “is not straightforward and often relies on rare-earth metals, which are increasingly scarce.” This challenge has recently led scientists to look for ways to produce white light more sustainably.

The researchers work at Justus Liebig University, Giessen, the University of Marburg, and Karlsruhe Institute of Technology. The team employed supercomputing resources from the High-Performance Computing Center Stuttgart (“HLRS”) in their discovery of cluster glass.

“We are witnessing the birth of white-light generation technology that can replace current light sources. It brings all the requirements that our society asks for: availability of resources, sustainability, biocompatibility,” said Prof. Dr. Simone Sanna, Giessen University Professor and lead computational researcher on the project.

‘Unexpected white light generation’

“My colleagues from the experimental sciences, who observed this unexpected white light generation, asked for theoretical support. Cluster glass has an incredible optical response, but we don’t understand why. Computational methods can help to understand those mechanisms. This is exactly the challenge that theoreticians want to face.”

Sanna and his collaborators turned to the power of high-performance computing, using the Hawk supercomputer at the High-Performance Computing Center Stuttgart to better understand cluster glass and how it might serve as a next-generation light source. They published their findings in Advanced Materials.

The team points out that glass is actually a class of materials that are considered “amorphous solids”, meaning they lack an ordered crystalline lattice, often due to a rapid cooling process in formation.

Their discovery announcement emphasized: “At the atomic level, their constituent particles are in a suspended, disordered state. Unlike crystal materials, where particles are orderly and symmetrical across a long molecular distance, glasses’ disorder at the molecular level make them ideal for bending, fragmenting, or reflecting light.”

Experimentalists from the University of Marburg recently synthesized “cluster glass.” Unlike a traditional glass that almost behaves as a liquid frozen in place, cluster glass, as the name implies, is a collection of separate clusters of molecules that behave as a powder at room temperature. They generate bright, clear, white light upon irradiation by infrared radiation.

New forms

Powders cannot easily be used to manufacture small, sensitive electronic components, but the researchers found a way to re-cast them in glass form: “When we melt the powder, we obtain a material that has all the characteristics of a glass and can be put in any form needed for a specific application,” Sanna said.

While experimentalists were able to synthesize the material and observe its luminous properties, the group turned to Sanna and HPChigh performance computing to better understand how cluster glass behaves the way it does. Sanna pointed out that white light generation is not a property of a single molecule in a system, but the collective behaviors of a group of molecules.

Modeling these processes at multiple scales is only possible using leading HPC resources like Hawk. HPC, said Sanna, makes it much faster to identify and test materials with novel optical properties. “We can predict the optical properties of a material that was synthesized by our chemist colleagues, and use these calculations to verify and better understand the material’s properties,” he said.

HPC speeds up R&D

HPC plays a major role in helping researchers accelerate the timeline between new discovery and new product or technology. Sanna explained that HPC drastically cut down on the time to get a better understanding of cluster glass.

“We spend a lot of time doing simulation, but it is much less than characterizing these materials in reality,” he said. “The clusters we model have a diamond-shaped core with four ligands (i.e. molecular chains) attached. Those ligands can be made of any number of things, so doing this in an experiment is time consuming.”

In ongoing studies of cluster glass Sanna’s team hopes to thoroughly understand the origin of its light generating properties. This could help to identify additional new materials and to determine how best to apply cluster glass in light generation.

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