Tiny Colour-Tunable Light Source Breakthrough

Tiny Colour-Tunable Light Source Breakthrough
4th August 2023 Moriah Aharon

Press release
Tiny switchable light sources:
Researchers at the Hebrew University Formed the Smallest Ever Light Source With Switchable Colours, Unleashing a New Era of Colour Tunable Nano-devices

(3 August 2023) New research from Hebrew University has achieved a significant breakthrough in colour switching for nanocrystals, unlocking exciting possibilities for a simple, energy efficient display design and for tunable light sources needed in numerous technologies. The discovery also has potential applications in sensitive sensors for various substances, including biological and neuroscience uses, as well as advancements in quantum communication technologies. This nanomaterial breakthrough holds the promise of inspiring exciting innovations in the future.

Uri Banin, Credit Yoram Aschheim

[Jerusalem, Israel] While nanocrystals offer colour tunability and are used in various technologies, achieving different colours requires using different nanocrystals for each colour, and dynamic switching between colours has not been possible. A team of Researchers at the Institute of Chemistry and The Centre for Nanoscience and Nanotechnology at The Hebrew University of Jerusalem, including graduate student Yonatan Ossia with seven other members, and led by Prof. Uri Banin, have now come up with an innovative solution to this problem. By developing a system of an “artificial molecule” made of two coupled semiconductor nanocrystals which emit light in two different colours, fast and instantaneous colour switching was demonstrated.

Coloured light and its tunability, are the basis to many essential modern day technologies: from lighting, displays, fast optical fiber-communication networks, and more. Upon taking colour emitting semiconductors to the nanoscale (nano- one billionth of a meter, one hundred thousand times smaller than a human hair), an effect called quantum confinement comes into play: changing the size of the nanocrystal modifies the colour of the emitted light. Thus, bright light sources can be obtained covering the entire visible spectrum. Due to the unique colour tunability of such nanocrystals, and their facile fabrication and manipulation using wet-chemistry, they are already widely used in high-quality commercial displays, giving them excellent colour quality along with significant energy saving characteristics. However, to this day, achieving different colours (such as needed for the different RGB pixels) required the use of different nanocrystals for each specific colour, and dynamical switching between the different colours was not possible.

Yonatan Ossia, Credit Yoav Ossia

Although colour tuning of single colloidal nanocrystals which behave as “Artificial atoms” has been previously investigated and implemented in prototype optoelectronic devices, changing colours actively has been challenging due to the diminished brightness inherently accompanying the effect, which only yielded a slight shift of the colour. The research team overcame this limitation, by creating a novel molecule with two emission centres, where an electric field can tune the relative emission from each centre, changing the colour, yet, without losing brightness. The artificial molecule can be made such that one of its constituent nanocrystals is tuned to emit “green” light, while the other “red” light. The emission of this new dual colour emitting artificial molecule is sensitive to external voltage inducing an electric field: one polarity of the field induces emission of light from the “red” centre, and switching the field to the other polarity, the colour emission is switched instantaneously to “green”, and vice versa. This colour switching phenomena is reversible and immediate, as it does not include any structural motion of the molecule. This allows to obtain each of the two colours, or any combination of them, simply by applying the appropriate voltage on the device. This ability to precisely control colour tuning in optoelectronic devices while preserving intensity, unlocks new possibilities in various fields including in displays, lighting, and nanoscale optoelectronic devices with adjustable colours, and also as a tool for sensitive field sensing for biological applications and neuroscience to follow the brain activity. Moreover, it allows to actively tune emission colours in single photon sources which are important for future quantum communication technologies.

Prof. Uri Banin from the Hebrew University of Jerusalem explained, “Our research is a big leap forward in nanomaterials for optoelectronics. This is an important step in our exposition of the idea of “nanocrystal chemistry” launched just a few years ago in our research group, where the nanocrystals are building blocks of artificial molecules with exciting new functionalities. Being able to switch colours so quickly and efficiently on the nanoscale as we have achieved has enormous possibilities. It could revolutionize advanced displays and create colour-switchable single photon sources.”

By utilizing such quantum dot molecules with two emission centres, several specific colours of light using the same nanostructure can be generated. This breakthrough opens doors to developing sensitive technologies for detecting and measuring electric fields. It also enables new display designs where each pixel can be individually controlled to produce different colours, simplifying the standard RGB display design to a smaller basis of pixels, which has the potential to increase the resolution and energy savings of future commercial displays. This advancement in electric field induced color switching has immense potential for transforming device customization and field sensing, paving the way for exciting future innovations.

Research Team: Prof. Uri Banim, Yonatan Ossia, Adar Levi, Yossef E. Panfil, Somnath Koley, Einav Scharf, Nadav Chefetz, Sergei Remennik, Atzmon Vakahi – Institute of Chemistry and The Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem,
For more information about the study, please refer to the article: Yonatan Ossia1,2, Adar Levi1,2, Yossef E. Panfil1,2, Somnath Koley1,2, Einav Scharf1,2, Nadav Chefetz1, Sergei Remennik2, Atzmon Vakahi2 and Uri Banin, “Electric field induced color switching in colloidal quantum dot molecules at room temperature” Nature Materials https://www.nature.com/articles/s41563-023-01606-0

Acknowledgement: The research leading to these results has received financial support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (project CoupledNC, grant agreement No [741767], and project CQDplay, grant agreement No [101069322]).

The Hebrew University of Jerusalem is Israel’s premier academic and research institution. With over 25,000 students from 90 countries, it is a hub for advancing scientific knowledge and holds a significant role in Israel’s civilian scientific research output, accounting for nearly 40% of it and has received over 11,000 patents. The university’s faculty and alumni have earned eight Nobel Prizes and a Fields Medal, underscoring their contributions to ground-breaking discoveries. In the global arena, the Hebrew University ranks 77th according to the Shanghai Ranking, making it the top-ranked Israeli institution. To learn more about the university’s academic programs, research initiatives, and achievements, visit the official website at http://new.huji.ac.il/en