When early humans discovered how to harness fire, they were able to push back into the nocturnal darkness that enveloped them. With the invention and widespread adoption of electricity, it became easier to separate heat from light, work at night, and light train cars on highways. In recent years, old forms of electric light generation such as halogen bulbs have given way to more energy-efficient alternatives, further reducing the cost to brighten our homes, workplaces and lives in general.
Unfortunately, however, producing white light from newer technologies such as light emitting diodes (LEDs) is not straightforward and often relies on a class of materials called “rare earth metals”, which are increasingly rare. This has recently led scientists to look for ways to produce white light more sustainably. Researchers at the University of Giessen, the University of Marburg and the Karlsruhe Institute of Technology recently discovered a new class of material called “cluster glass” that shows great potential for replacing LEDs in many applications.
“We are witnessing the birth of white light production technology that can replace current light sources. It brings all the requirements that our society asks for: availability of resources, sustainability, biocompatibility,” said Professor Dr. Simone Sanna, Professor at the University of Giessen and lead computational researcher on the project.
“My colleagues from experimental sciences, who observed this unexpected generation of white light, asked for theoretical support. Cluster glass has an incredible optical response, but we do not understand why. Computational methods can help to understand these mechanisms. This is exactly the challenge that theorists want to face.”
Sanna and colleagues have turned to the power of high-performance computing (HPC), using the Hawk supercomputer at the High-Performance Computing Center Stuttgart (HLRS) to better understand cluster glass and how it could serve as a next-generation light source . They published their findings in Advanced Materials.
Clear-eyed view of cluster glass formation
If you’re not a materials scientist or chemist, the word glass might just mean the clear, solid material in your windows or on your dinner table. Glass is actually a class of materials that are considered “amorphous solids”. That is, they lack an ordered crystal lattice, often due to a rapid cooling process. At the atomic level, their constituent particles are in a suspended, disordered state. Unlike crystalline materials, where the particles are ordered and symmetrical over a long molecular distance, the disorder of glasses at the molecular level makes them excellent for bending, shattering or reflecting light.
Experimenters from the University of Marburg recently synthesized a particular glass called “cluster glass”. Unlike a traditional glass that almost behaves as a liquid frozen in place, cluster glass, as the name suggests, is a collection of individual clusters of molecules that behave as a powder at room temperature. They produce bright, clear, white light when irradiated by infrared radiation. While the powders cannot easily be used to make small, sensitive electronic components, the researchers have found a way to recast them in glass form: “When we melt the powder, we get a material that has all the characteristics of a glass and can be put into whatever format is needed for a particular application,” Sanna said.
Structural modifications of molecular clusters leading to the formation of amorphous compounds can be induced by electron or laser irradiation. Credit: Elisa Monte, Justus-Liebig-Universität Gießen
While the experimenters were able to synthesize the material and observe its luminous properties, the team turned to Sanna and HPC to better understand how the cluster glass behaves the way it does. Sanna pointed out that the production of white light is not a property of a single molecule in a system, but the collective behavior of a group of molecules. Therefore, mapping the interactions of these molecules with each other and with their environment in a simulation means that researchers must capture the large-scale behaviors of light production and also observe how small-scale atomic interactions affect the system. Any of these factors would be computationally difficult. However, modeling these processes at multiple scales is only possible using leading HPC resources such as Hawk.
Collaboration between experimentalists and theorists has become increasingly important in materials science, as synthesizing multiple iterations of a similar material can be slow and expensive. High-performance computers, Sanna said, make it much faster to identify and test materials with new optical properties. “The relationship between theory and experiment is a continuous loop. We can predict the optical properties of a material synthesized by our fellow chemists and use these calculations to verify and better understand the properties of the material,” said Sanna. “We can also design new materials on a computer, providing information that chemists can use to focus on synthesizing compounds that have the greatest chance of being useful. In this way, our models inspire the synthesis of new compounds with tailored optics properties”.
In the case of cluster glass, this approach led to a simulation-verified experiment, with the modeling helping to show researchers the relationship between the observed optical properties and the molecular structure of the cluster glass material, and they can now move forward as a candidate for replacing light sources that are heavily dependent on rare earth metals.
HPC accelerates R&D timelines
HPC plays an important role in helping researchers speed up the timeline between a new discovery and a new product or technology. Sanna explained that HPC drastically reduced the time to better understand cluster glass. “We spend a lot of time doing simulation, but it’s much less than actually characterizing these materials,” he said. “The complexes we model have a diamond-shaped core with 4 ligands (molecular chains) attached to it. These ligands can be made of many things, so doing this in an experiment is time-consuming.”
Sanna pointed out that the team is still limited by how long they can run individual runs for their simulations. Many research projects on supercomputers can divide a complex system into many small parts and perform calculations on each part in parallel. Sanna’s team must pay close attention to long-range particle interactions in large systems, so they are limited by how far they can divide their simulation into computer nodes. He said regular access to longer runtimes—more than a day at a time on a supercomputer—would allow the team to work faster.
In ongoing studies of cluster glass, Sanna’s team hopes to fully understand the origin of its light-producing properties. This could help identify additional new materials and determine how best to apply cluster glazing to light generation.
Sanna explained that the HPC resources at HLRS were essential to his team’s basic science research, which he hopes will lead to new products that can benefit society. “The main computational achievement in this journal article was only possible through our access to the machine in Stuttgart,” he said.
New glass-ceramic emits light when subjected to mechanical stress More information: Irán Rojas-León et al, Cluster-Glass for Low-Cost White-Light Emission, Advanced Materials (2022). DOI: 10.1002/adma.202203351
Provided by the High-Performance Computing Center Stuttgart
Reference: Identification of a new, cleaner source for white light (2022, August 16) Retrieved August 16, 2022, from
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