By Jay Kakade 26 Nov, 2024
Collected at: https://www.techexplorist.com/advancement-solid-state-optical-cooling-quantum-dots/93472/
In a recent study, researchers from Chiba University have proposed a promising approach for solid-state optical cooling using quantum dots based on perovskite materials. This research is focused on anti-Stokes photoluminescence, and the team asserts a revolution in the existing cooling technology.
Since heat wears down materials and degrades performance in modern technologies, cooling systems play a vital role in smooth functioning. However, cooling tends to be an inconvenient and energy-intensive process.
Therefore, scientists are keen to look forward to an efficient cooling system. Solid-state optical cooling is a proficient example that utilizes the phenomenon of Anti-Stokes (AS) emission.
Usually, when a material absorbs incoming light, its electrons transition into an “excited” state. When these electrons return to their normal state, some energy is released as light, and the rest is dismissed as heat.
However, in materials that undergo AS emission, electrons interact with crystal lattice vibrations so that the light emitted is of higher energy than the incident light. Researchers think when the AS emission is about 100%, the material theoretically cools down rather than heating up. However, there have been challenges in achieving 100% efficiency.
In the efforts to achieve Optical Cooling in semiconductors, a team of researchers led by Professor Yasuhiro Yamada has encountered quantum dots. While quantum dots are reliable for high emission efficiency, they are generally unstable and easily degrade on exposure to light and air.
Thus, the team has proposed a stable structure in a special arrangement of perovskite quantum dots and dots-in-crystals.
“Efforts to achieve optical cooling in semiconductors have encountered several difficulties, primarily due to challenges in reaching nearly 100% emission efficiency, and true cooling has been elusive,” says the lead author Yamada.
“Though quantum dots are promising for their high emission efficiency, they are notoriously unstable, and exposure to air and continued illumination degrade their emission efficiency. Thus, we focused on a stable structure known as ‘dots-in-crystals,’ which may overcome these limitations,” Yamada continues.
However, using quantum dots in semiconductors is still a mystery. The irradiation with high-intensity light in semiconductor quantum dots often leads to heating instead of cooling.
To investigate, researchers used time-resolved spectroscopy to examine conditions in which energy is released as heat instead of light. These experiments revealed that heating was unavoidable even at moderate light intensity. Meanwhile, at low-intensity light, the cooling became ineffective.
“Previous reports of optical cooling in semiconductors lacked reliability, primarily due to flaws in temperature estimation. Our study, however, not only established a reliable method but also defined the potential and limitations of optical cooling through time-resolved spectroscopy, marking a significant achievement in the field,” says Yamada.
The lead authors assert that the study has paved the way for future researchers to focus on improving the cooling performance of dots-in-crystal arrangements. Researchers have also posited its contribution to global sustainability goals.
Journal Reference
- Yasuhiro Yamada, Takeru Oki, Takeshi Morita, Takumi Yamada, Mitsuki Fukuda, Shuhei Ichikawa, Kazunobu Kojima, and Yoshihiko Kanemitsu. Optical Cooling of Dot-in-Crystal Halide Perovskites: Challenges of Nonlinear Exciton Recombination. Nano Letters 2024. DOI: 10.1021/acs.nanolett.4c02885
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