Thermal and nonthermal exciton light emissions from carbon nanotubes above 1000 K

High-temperature light emission from nanomaterials has been extensively studied for light-emitting device applications. However, thermodynamic properties of their light emission under high-temperature conditions, which are critical for energy applications, have not been fully elucidated. Herein, we demonstrate that carbon nanotubes emit nonthermal light, specifically exciton luminescence in the near-infrared (NIR) region, even at very high temperatures. By investigating the chemical potential of photons, which indicates an extent of nonthermal excitation beyond thermal equilibrium, we show that exciton light emission from a semiconducting nanotube maintains a nonthermal condition above 1000 K, enabling intense radiation that exceeds thermal radiation at the same temperature. Furthermore, the chemical potential of photons emitted by an individual metallic nanotube under electric-current injection far surpasses that of semiconducting nanotubes at ≈ 1000 K. These findings facilitate applications of carbon nanotubes as high-intensity, narrow-band NIR emitters operable even at very high temperatures for advanced energy-conversion devices. The thermodynamic properties of high-temperature light-emitting nanomaterials are important in energy applications but are still not fully understood. Here, it is found that carbon nanotubes emit nonthermal light in the near-infrared region, even at very high temperatures.