Scientists Have Discovered Why Silver Clusters Emit Light

New research finds why silver clusters emit light opening new possibilities for practical applications in lighting, imaging, and therapeutics.

Silver clusters confined in matrices possess remarkable luminescence properties, but little is known about their structural and electronic properties, or at least until now.  

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Thanks to an interdisciplinary team of physicists and chemists led by The Katholieke Universiteit Leuven (KU Leuven) in Belgium, now we know exactly how and why clusters of silver atoms captured in zeolites have such remarkable light-emitting properties. 

This recent discovery plays a paramount role opening new possibilities for more efficient lighting applications that could become a better alternative for LED and TL lamps, contributing to the efforts of energy efficiency.

When clusters of silver atoms are captured in zeolites, a porous material with small channels and voids, they present remarkable light-emitting properties. The researchers have now demonstrated the origin of these properties for the first time.

What are zeolites and why this is important 

Zeolites are microporous, aluminosilicate minerals. They occur naturally but are also produced industrially. In 1756, Swedish mineralogist, chemist, and one of the founders of modern mineralogy Axel Fredrik Cronstedt coined the term zeolite (from the Greek ζέω (zéō), to boil and λίθος (líthos), stone) after observing that rapidly heating the material produced large amounts of steam from water that it had been absorbed. 

In chemistry, zeolites are used to separate molecules and as traps for molecules so they can be analyzed. Molecules have to be of certain sizes and shapes in order to be able to pass through.

Scientists use zeolites to simulate certain reactions. When molecules are caught in the voids of the zeolites they lose mobility and start behaving differently. This observation allowed the researchers at KU Leuven to discover why and how silver clusters emit light when they are trapped in the cages of a specific type of zeolite. 

zeolites
Source: Wikimedia Commons
 

According to Didier Grandjean, a researcher at the Laboratory of Solid State Physics and Magnetism unit at KU Leuven, the team of researchers irradiated a mixture of silver clusters with synchrotron radiation at the European Synchrotron Radiation Facility in Grenoble.

"What is good about this is that it provides us with a lot of information on the structure and properties of the material. However, as we specifically wanted to look at the optical properties, we used a new method that deliberately only measured the emitted light. This way, we were sure that we were only looking at the specific particles responsible for the light," said Grandjean.

The research conducted by the KU Leuven scientists provided conclusive and clear evidence that only very small clusters of four silver atoms in the form of a tetrahedron and surrounded by water molecules emit light.

The glow of silver clusters

According to Professor Peter Lievens, professor in experimental physics in the Department of Physics and Astronomy of the KU Leuven, the tetrahedra form a unit in which two electrons can move freely. "This forms a so-called super atom: a structure composed of several atoms, but behaving very much like a single atom," says Professor Lievens.

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"The optical properties of the clusters are caused by the two free electrons. These decay from a higher to a lower energy level, resulting in a certain shade of green light. In turn, the energy levels are determined by the chemical properties of the super atom," he says. 

The new observation is the result of an intense collaboration between researchers in both chemistry and physics. According to Professor Lievens, the experimental observations are confirmed by advanced theoretical calculations. 

The findings serve as the grounds for identifying candidate materials through modifying the properties of silver clusters looking for the desired optical properties which can be used for practical multiple applications in lighting, imaging, and therapeutics. 

The scientists summarized their study in the research paper Origin of the Bright Photoluminescence of Few-Atom Silver Clusters Confined in LTA Zeolites, which was published in the peer-reviewed academic journal Science on August 17, 2018.

Via: KU Leuven

 

 

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