Researchers at Cambridge have developed a new light-emitting system that could eventually improve cancer imaging, smartphone screens and low-energy computing.
The discovery emerged from a collaboration between physicist Dr Rakesh Arul and chemists Dr Huangtianzhi Zhu and Dr Zhongzheng Yu in the laboratory of Professor Akshay Rao, after they noticed an unexpected effect in molecules attached to microscopic particles containing rare-earth metals.
“We were seeing surprisingly bright emission from states that are normally considered optically dark,” said Dr Arul, a Research Fellow at St John’s College, University of Cambridge, and co-first author of the paper with Dr Zhu.
“In the process of unravelling the mystery, we found that this bright emission came from a normally dark molecular state, the triplet, which is conventionally forbidden from emitting light via the rules of quantum mechanics.”
The research, published in Nature Chemistry, centres on “triplet states” – excited molecular states that are crucial in technologies ranging from OLED displays and televisions to solar energy systems, but are usually difficult to control because they interact weakly with light.
The Cambridge team found they could make these normally “spin-forbidden” states emit light by coupling the spin of the molecule to the spins of nearby lanthanide ions – metallic elements used in lasers and advanced optics.
“We subsequently found we could engineer the triplet state of various molecules to be bright by coupling the spin of the molecule to the spin of nearby lanthanide ions, allowing the triplet state to be directly excited and to emit light at room temperature, even in solution,” Dr Zhu said.
“In the process of unravelling the mystery, we found that this bright emission came from a normally dark molecular state, which is conventionally forbidden from emitting light via the rules of quantum mechanics”
The result is a persistent afterglow – known as phosphorescence – that remains stable even in air.
“What is new here is that this works at room temperature, in solution, and under ambient conditions, rather than only in crystals, rigid hosts, or oxygen-free environments,” Dr Yu said.
Researchers say the discovery could improve medical imaging because longer-lasting light signals are easier for scanners to distinguish from surrounding tissue. In practical terms, that could help doctors detect smaller tumours or track biological processes more accurately.
The same principle could also help reduce energy consumption in consumer electronics. Modern OLED screens, sensors and optical chips waste significant amounts of power because excited energy states disappear too quickly.
“Triplets are central to organic electronics, solar energy conversion, photocatalysis, imaging and OLEDs, but they can be challenging to access and make bright,” said Professor Rao, a former St John’s College Research Associate. “This work shows a new way to control triplets using spin coupling, opening a route to brighter organic materials and new light-based technologies.”
The team said they were particularly surprised that the glow remained bright even in the presence of oxygen, which usually suppresses triplet emissions extremely quickly.
“The most surprising result was how robust the emission was,” Dr Arul said. “Oxygen normally quenches triplet states very efficiently, but in these hybrids the triplet emission remained bright in solution under ambient conditions.”
Dr Arul said the next stage of the research would focus on using the system for “quantum sensing, quantum networks, and molecular-scale control of spin states”.
