Hebrew University researchers have created the smallest color switch in the world

The quick color switch allows an immediate change of the emitted color. The discovery has implications for diverse technologies in which fast color adjustment is required, such as display screens, quantum communication and miniaturized light sources

A team of researchers from the Hebrew University discovered a new phenomenon of controlled, immediate, and reversible light switching in a single nanocrystal capable of emitting light in two different colors. The nanocrystal consists of two conjugated centers that emit light, and can be switched between them by applying an appropriate electric field to the conjugated crystal, which is a kind of "artificial molecule" composed of two different nanocrystals, and allows the emission of light from any of the colors or any combination of them. For the discovery of applied implications for diverse technologies including in display screens, for creating tiny light sources, for quantum communication, whispering electric fields in neuron research and more.

Changing the size and composition of semiconductor nano-crystals allows for the adjustment of the color of the light emitted from them. This phenomenon has many applications. For example in display screens, where the color image is obtained by combining the three basic colors - red, green and blue. At the same time, for each color it is necessary to use a different nano crystal, and immediate switching between different colors has not been possible until now.

A group of researchers from the Institute of Chemistry and the Center for Nanoscience and Nanotechnology of the Hebrew University, which includes research student Yonatan Ossiah and other researchers, led by Professor Uri Benin, succeeded for the first time in demonstrating the existence of a new phenomenon that enables fast and reversible color switching in an 'artificial molecule' system consisting of two conjugated nanocrystals that emit two different colors. For the discovery of significant technological implications and potential for application in the world of screens and other fields. The findings of the groundbreaking research were published in the prestigious journal Nature Materials.

The emission of colored light from semiconductor materials is the basis for a variety of important technologies such as economical and miniaturized lighting, new screens, fast optical communication networks, sensing, and more. By reducing the size of a semiconductor particle to the nanometer range (a nanometer - a billionth of a meter, one hundred thousandth of the diameter of a hair), a nano crystal is obtained which is sometimes called an "artificial atom". One of the wonderful properties of nano crystals made of semiconductors is a strong light emission, and the possibility to control the color of the light by changing the size of the crystal. For this reason, semi-conducting nano-crystals are used as light sources for the various colors of the rainbow. This feature is already widely used today in TV screens where the pixels are composed of nano crystals that give the screen excellent color quality, at the same time as energy saving. At the same time, until now, obtaining the different colors required to obtain the color range on the screen (red, green, blue) has only been possible by using different nano-crystals adapted to each color and pixel separately, and it was not possible to use one type of nano-crystal to obtain several colors Different.  

In the scientific breakthrough, to achieve the new switching phenomenon, the research team created a new type of nanocrystal consisting of two nanocrystals, each of which is tuned to emit light of a different color. This is how a structure with properties of an artificial molecule was obtained. In this way, for example - you can join together a nano crystal that emits green light, with a second nano crystal that emits red light and get a single particle that emits light in two different colors. The researchers showed that it is possible to switch and adjust the color of the light emitted from such a molecule by applying an external electric field by applying voltage to an array of electrodes. At one polarity of the field, the emitted light will be red, and at the reversal of the electric voltage, the emitted light will be green. In this way, the colors can be switched from red to green, reversibly and quickly. Moreover - under the application of a suitable voltage, any desired combination of color between green and red can also be obtained - which allows the deployment of a diverse color space from a single particle.

This discovery has far-reaching practical implications in a variety of fields: in screens, it will make it possible to greatly simplify the structure of the screen and obtain a high resolution with fewer different pixels. Instead of a different pixel structure for each of the three primary colors (red, green and blue), a pair of pixels can be replaced with a single pixel where the light will switch between two colors as needed. The discovery also opens up new possibilities in regards to color-coded laser technologies, optical and quantum communication technologies that require unique light sources with defined colors, and even as a new means of sensing electric fields by optical means that is required in brain research.

Prof. Benin explained the significance of the discovery and said "Our discovery is a significant advance in the combination of nanomaterials and opto-electronic devices. This is an important step in the development of the concept of 'nanocrystal-based chemistry' in which nanocrystals are used as artificial atoms and building blocks for a variety of artificial molecules with new properties, a field we introduced for the first time only a few years ago." He added, "The ability to switch and change colors quickly and efficiently as we were able to achieve, is important and relevant to a variety of technologies. For example - in the field of screens it is possible to simplify the structure of the screen which is required for the production of new miniaturized screens, as well as in the innovative field of quantum communication where new light sources are required that emit single photons and whose color can be switched quickly. The discovery is also relevant to various fields of research, for example the field of neurobiology where remote sensing of a local electric field using light emission is required."

The research team included the following researchers: Prof. Uri Benin, Yonatan Osia, Ader Levy, Yosef Ephraim Panfil, Somanat Kuli, Einav Sharaf, Nadav Hefetz, from the Institute of Chemistry, and Sergey Ramnik, and Atzmon Vakehi from the Center for Nanoscience and Nanotechnology of the Hebrew University of Jerusalem. The research leading to these results received financial support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program.

Article link: https://www.nature.com/articles/s41563-023-01606-0

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