Discovery could lead to next-gen fluoro and LED lighting

The discovery of a new phosphor could lead to cheaper and more efficient fluorescent and LED lighting, according to new research from Europe.

A team from KU Leuven in Belgium, France’s University of Strasbourg and the Paris-based Centre National de la Recherche Scientifique (CNRS) has been working with highly luminescent clusters of silver atoms and the porous framework of minerals known as zeolites. Silver clusters consist of a few silver atoms and have remarkable optical properties but limited application, as the clusters tend to aggregate into larger particles, which inhibits these optical properties.

The study is being lead by Professor Johan Kofkens of KU Leuven’s Molecular Imaging and Photonics Unit. He and his team have found a way to separate the silver clusters by inserting them into the porous zeolite framework.

Zeolites are minerals that are either found in nature or produced synthetically on an industrial scale. They have a very rigid and well-defined framework of small molecular-sized channels, pores and cages and are commonly used in domestic and industrial applications, such as washing detergent and water treatment.

Professor Maarten Roeffaers from KU Leuven’s Centre for Surface Chemistry and Catalysis explained: “Zeolites contain sodium or potassium ions. We used ion exchange to replace these ions with silver ions. To obtain the clusters we wanted, we heated up the zeolites with the silver ions so that the silver ions self-assembled into clusters.”

In collaboration with Professor Peter Lievens’s Laboratory for Solid State Physics and Magnetism at KU Leuven, the researchers examined the properties of these heat-treated ‘silver zeolites’. Using advanced techniques, they found that the structural, electronic and optical properties of the zeolites were strongly influenced by the silver clusters. That’s how they discovered that the shape of the silver clusters is essential to obtain the right fluorescence properties.

Hofkens explained, “Clusters of silver atoms can assemble into different shapes, including a line or a pyramid. This pyramid shape is what we need to obtain the best fluorescence properties. Heating up the silver ions in the zeolite framework makes them adopt this shape. Because they are ‘trapped’, as it were, in the cages of the zeolites, they can only form a pyramid with up to four silver atoms. That is exactly the shape and size in which the silver cluster emits the largest amount of fluorescent light, with an efficiency close to 100%.”

These findings have great potential for the development of next-generation fluorescent and LED lighting and for biological imaging, as the new phosphors not only emit a large amount of light, but are also cheap to produce. The research is available from the journal Nature Materials .