Carbon Nanotubes Couple Light And Matter

Researchers from Heidelberg and St Andrews are working on the foundations of new light sources from organic semiconductors

With their research on nanomaterials for optoelectronics, scientists at the University of Heidelberg and the University of St Andrews (Scotland) have succeeded in demonstrating for the first time a strong interaction of light and matter in semiconducting carbon nanotubes. This strong light-matter coupling is an important basis for the realization of new light sources, so-called electrically pumped lasers, which are to be produced on the basis of organic semiconductors and which would be important for applications in the telecommunications sector. The research results from the collaboration of Prof. Dr. Jana Zaumseil (Heidelberg) and Prof. Dr. Malte Gather (St Andrews) were published in "Nature Communications".

Organic semiconductors based on carbon are a cost-effective and energy-efficient alternative to conventional inorganic semiconductors such as silicon. For example, light-emitting diodes, which consist of these materials, are already widely used in displays of smartphones. Further components for applications in lighting technology, data transmission and photovoltaics are in prototype status. However, an important component of optoelectronics has not yet been realized with organic materials - the electrically pumped laser. This is mainly due to the fact that organic semiconductors are only in a limited capacity to transport charges, ie current.

As Prof. Zaumseil explains, the laser-like light emission of organic semiconductors on the basis of light-matter coupling has increasingly been the focus of research in recent years. If photons (light) and excitons (matter) are brought together with sufficiently great interaction, they couple so strongly that so-called exciton polaritons arise. These are quasi-particles, which also emit light. Under certain conditions, this emission can take on the properties of laser light. With sufficient charge transport, exciton polaritons would make the production of an electrically pumped carbon-based laser within reach, Jana Zaumseil, who heads the research group "Nanomaterials for Optoelectronics" at the Physikalisch-Chemisches Institut of the University of Heidelberg.

Within the framework of the collaboration between Prof. Zaumseil and Prof. Gather, the formation of exciton polaritons in semiconducting carbon nanotubes was demonstrated for the first time. In contrast to other organic semiconductors, these microscopic, tubular structures of carbon carry positive and negative charges very well. They also show exceptional optical properties, such as doctoral student Arko Graf, who is the first author of the study. The researchers at Heidelberg and St Andrews see their research results as an important step towards the realization of electrically pumped lasers based on organic semiconductors. "In addition to the potential production of laser light, we can already move the near-infrared light emitted by the carbon nanotubes over large wavelength ranges using the exciton polaritons," emphasizes Prof. Zaumseil.