Copper’s Surprising Role in Green Lighting

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NORMAN, OKLA. – University of Oklahoma researchers have unveiled a novel method of creating smart luminescent materials that change their light-emitting properties when exposed to different heat or chemical conditions. This discovery, published in the journal Aggregate, could lead to advancements in radiation detection, anti-counterfeiting technologies, information storage and LED lighting.

“In recent years, the field of materials science has devoted a great deal of attention to metal halides,” said Bayram Saparov, an OU associate professor and principal investigator on the study. “These materials are exciting because they’re inexpensive and don’t contain rare elements from the Earth’s crust. That means thy can be processed much cheaper than other materials that require either costly rare elements or expensive processing conditions, such as high temperatures or vacuum processing.”

Metal halides are a class of recently discovered semiconductors used in lighting displays and solar energy panels, as well as in light and radiation detection. Traditionally, these materials contain the toxic element lead. However, Saparov’s team employed copper halides, which are easy to process, inexpensive and have earth-abundant chemical compositions.

“They also have very interesting optical and electronic properties,” he said. “Dilruba Popy, one of my graduate students, synthesized two new copper halides that have fantastic orange and green light emissions that are nearly 100% efficient.”

Popy studied the atomic and electronic structures of these copper halides to better understand their optical properties – why one emits green light and the other orange. She also investigated their phosphorescence, which is important when detecting high-energy radiation like X-rays or gamma rays that are invisible to the human eye. She determined that these halides could convert radiation into visible green and orange light.

Importantly, Popy was able to demonstrate this photoluminescence at room temperature. Most chemicals only glow in the dark at extremely low temperatures. According to Saparov, these copper halides show photoluminescence at room temperature because they lack thermal quenching – a process by which a material's light emission decreases as it gets hotter because the heat disrupts the energy processes that produce the light.

“Because of this luminescence, these materials can also be used for anti-counterfeiting applications in which invisible marks or fingerprints are made on an official document that can only be seen under UV light of a certain wavelength,” Saparov said. “Dilruba was able to demonstrate this by making encrypted patterns utilizing her orange and green emitting materials.”

Popy also discovered that copper halides are very efficient light emitters and are stable in open air, which isn’t always the case with metal halides. They can also be processed under high temperature conditions, which is rare for metal halides because they tend to decompose or degrade when melted. These discoveries mean that these materials can be used in LED lighting and to create thin films used in screen displays.

“Our lab will continue to study the light emission properties of this material so that we can fine tune their optical properties. I’m proud of the work Dilruba has done publishing this paper and for the knowledge we have gained throughout our research.”

Learn more about Saparov’s research in solid state and materials chemistry at OU.