When graphene starts to glow without heating up
In a semiconductor, electrons can accumulate energy in excited states, separated from their rest states by a band gap. It is this accumulation that enables the emission of ‘cold’ light, as in light-emitting diodes (LEDs). Metals, on the other hand, do not have this band gap: their electrons release their energy very quickly in the form of heat and incandescent light, making electroluminescence impossible… at least until now.
Graphene, a two-dimensional material consisting of a single layer of carbon atoms, is an exception to this rule and can also become electroluminescent under certain conditions. This discovery, published in the journal Nature, is based on the use of very high-quality graphene encapsulated in hexagonal boron nitride (hBN), which preserves the material’s unusual electronic properties.
Graphene is a semi-metal with ultra-mobile electrons that are weakly coupled to their environment and can reach electronic states far from thermal equilibrium. In this extreme regime, we observed infrared light emission consistent with electroluminescence, rather than simple incandescence. This makes graphene the first known electroluminescent ‘metal’.
Beyond light emission, this work highlights another phenomenon: a particularly efficient transfer of radiative energy between graphene and its substrate. In fact, up to 70% of the energy dissipated by the electric current is transferred to the substrate via electromagnetic interactions, notably through the excitation of hyperbolic phonon-polaritons in hBN.
These quasi-particles, resulting from the coupling between photons and vibrations in the crystal lattice, enable energy to be transferred over a distance without thermal conduction and therefore without heating.
This discovery challenges the traditional limits of electroluminescence and opens up new prospects for the design of light sources in the infrared range, a crucial field for telecommunications and detection. Graphene’s ability to emit light without significant heating could also lead to more efficient and compact optoelectronic devices with potential applications in nanophotonics or for very small-scale integrated light sources.
Graphene electroluminescence illustration generated by DALL·E. @Credit: PhD thesis of Aurélien Schmitt (2023)
Référence:
Electroluminescence and energy transfer mediated by hyperbolic polaritons, Loubnan Abou-Hamdan et al, Nature 639, 909 (2025) ;
Contact :
david.mele
junia.com
