When graphene starts to glow without heating up
It is a rule that every physics student learns: “metals cannot be electroluminescent.” However, a team of researchers from several laboratories, including the IEMN, has just demonstrated that graphene, a material with metallic behavior, can emit light without heating up, a phenomenon previously thought to be exclusive to semiconductors. This unprecedented electroluminescence, observed in the infrared range, opens up new perspectives for more efficient and miniaturized light sources.
Electroluminescence refers to the emission of light induced by an electric current, without significant heat generation. It underpins many modern technologies, from flat-panel displays to laser diodes. Until now, this effect was believed to be limited to semiconductors and considered fundamentally inaccessible to metals.
In semiconductors, electrons can be excited into higher energy states, separated from lower-energy states by a bandgap. This energy can then be released as ‘cold’ light as seen in light-emitting diodes (LEDs). In contrast, metals lack such a bandgap: their electrons typically relax too rapidly, dissipating energy as heat and incandescent light, which renders electroluminescence impossible… or so we thought.
Graphene, a two-dimensional material consisting of a single layer of carbon atoms arranged in a honeycomb lattice, defies this expectation. Under specific conditions, it can exhibit electroluminescence. This breakthrough, published in Nature, relies on the use of ultra-high-quality graphene encapsulated in hexagonal boron nitride (hBN), which preserves the the material’s intrinsic and unusual electronic properties.
Beyond this light emission, the study reveals another key phenomenon: a remarkably efficient transfer of radiative energy between graphene and its substrate. Up to 70% of the energy dissipated by the electrical current is transferred to the substrate via electromagnetic interactions, particularly through the excitation of hyperbolic phonon-polaritons in hBN.
These quasi-particles, arising from the coupling of photons with vibrational modes in the crystal lattice, allow energy to propagate without relying on thermal conduction and therefore without significant heating.
This discovery challenges the conventional limits of electroluminescence and opens new avenues for designing light sources in the infrared domain, which is vital for telecommunications and sensing. Graphene’s ability to emit light with minimal heating may pave the way for more efficient, compact optoelectronic devices, with promising applications in nanophotonics and ultra-miniaturized 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) ;
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