The advance centres on lanthanide-doped nanoparticles, materials long valued for their ability to emit unusually pure and stable light, especially in the second near-infrared range. That part of the spectrum is important because it can travel deeper through biological tissue than visible light, making it attractive for medical diagnostics and imaging. The problem has been electrical: the particles are excellent light emitters but poor conductors, leaving them largely incompatible with standard electronic devices.
Scientists at the University of Cambridge’s Cavendish Laboratory have now found a way around that barrier by attaching organic molecules to the surface of the nanoparticles. These molecules act as tiny antennas, taking in electrical energy and passing it to the particles indirectly rather than forcing current through materials that normally resist it.
The resulting devices, described as lanthanide nanoparticle LEDs, switch on at about 5 volts and emit near-infrared light with a narrow spectral width. That makes the output more precise than many competing light-emitting technologies, including quantum dots, whose broader emission profiles can create unwanted signal overlap in applications requiring high wavelength accuracy.
The team used 9-anthracenecarboxylic acid, known as 9-ACA, as the organic antenna. Electrical charges are injected into these attached molecules, which then enter an excited triplet state. Triplet states are often treated as energy losses in optical systems because they do not readily produce light. In this design, however, more than 98 per cent of that energy is transferred to lanthanide ions inside the insulating nanoparticles, causing them to emit light efficiently.
Professor Akshay Rao, who led the work, described the approach as a “back door” into materials that had been difficult to power directly. The molecules, he said, catch charge carriers and pass energy to the nanoparticle through a triplet energy transfer process that proved unexpectedly effective.
The first-generation devices achieved a peak external quantum efficiency above 0.6 per cent for NIR-II LEDs. That figure is modest compared with mature commercial LED platforms, but researchers regard it as significant because the devices are built from a class of nanoparticles previously considered unsuitable for direct electrical activation under normal operating conditions.
The implications are broad. Near-infrared light is already used in biomedical sensing, imaging and therapeutic research because it can pass through tissue with lower scattering and reduced background interference. A compact LED that produces highly specific near-infrared wavelengths could support wearable or injectable diagnostic tools, help monitor organ function, improve tumour imaging, or activate light-sensitive drugs with greater precision.
Optical communications could also benefit from purer emission. Data transmission systems depend on tightly controlled wavelengths to reduce interference and improve signal clarity. Narrow-band near-infrared emitters could eventually help create compact components for communication networks, especially where stability and wavelength precision are essential.
The technology may also strengthen chemical and biological sensing. Sensors designed to detect specific molecules often rely on clean light signals that match narrow absorption or emission bands. A platform that can be tuned by combining different organic antennas and insulating nanomaterials could allow engineers to design devices for selected biomarkers, environmental pollutants or industrial gases.
The breakthrough sits at the intersection of organic electronics, nanophotonics and materials chemistry. Rather than treating insulating behaviour as a dead end, the Cambridge team changed the energy delivery route. That principle could be extended to other insulating nanomaterials whose optical properties are attractive but whose lack of electrical conductivity has limited device integration.
Dr Zhongzheng Yu, a lead researcher on the project, said the purity of light in the second near-infrared window is a major advantage for biomedical sensing and optical communications, where sharply defined wavelengths are needed. Dr Yunzhou Deng, another member of the team, said the platform opens a new class of materials for optoelectronics because different combinations of antennas and nanomaterials can now be explored.
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