Carbon nanotubes (CNTs) have been gaining traction as a sustainable solution to the thermal management of high-density server racks. These require the effective dissipation of the heat generated by the processors to ensure reliable performance. Researchers at The Institute of Physical and Chemical Research (RIKEN) in Japan have shown that carbon nanotubes (CNTs) can emit light with a higher energy than the light incident upon them, potentially opening the door to opto-thermal cooling technologies.

The Use of CNTs in Up-Conversion Photoluminescence

Up-conversion photoluminescence (UCPL) is the effect where an exciton – a quasiparticle formed of an electron and a positively charged hole – interacts with a phonon – a quasiparticle formed of vibrational energy – in a single-walled CNT to carry away more light energy than was put in. 

Previous theories have suggested that UCPL occurs only in single-walled CNTs, where a defect in the structure briefly traps the excitons. However, the research team at RIKEN demonstrated that UCPL occurs in nanotubes without any defects, disproving the old theory.

The researchers showed that phonons within the CNTs boost the energy of an electron simultaneously excited by light, forming a state known as a ‘dark exciton’. This theory was confirmed in experiments where increased UCPL was seen at higher temperatures due to the increased abundance of phonons.

What Does This Mean for CNT-Based Opto-Thermal Cooling?

Traditional cooling systems for high-density server racks are unsustainable, consuming large amounts of energy. The use of CNTs offers a potential solution through opto-thermal cooling. The UCPL process uses a laser to convert low-energy infrared light into higher-energy light, which carries the heat away. 

This process could reduce the energy consumption required for cooling by 30%. Sustainability benefits are also provided by reducing the use of resource-intensive materials. Therefore, CNTs have the potential to revolutionise thermal regulation and optical networking while also improving sustainability.

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Intrinsic process for upconversion photoluminescence via 𝐾-momentum–phonon coupling in CNTs