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Engineers are observing avalanches in nanoparticles for the first time

Colombian engineers first observed avalanches in nanoparticles

Illustration of the chain reaction process that underlies the avalanche mechanism of photons Columbia Engineering researchers have realized in their nanoparticles. In this process, the absorption of a single low-energy photon causes a chain reaction of energy transfers and further absorption events, which lead to very strongly excited ions in the nanoparticle, which then release their energy during intense emission of much higher-energy photons. Credit: Mikołaj Łukaszewicz / Polish Academy of Sciences

Researchers at Columbia Engineering today announced that they have developed the first nanomaterial to demonstrate a “photon avalanche,” a process that is unsurpassed in its combination of extreme nonlinear optical behavior and efficiency. The realization of an avalanche of photons in the form of nanoparticles opens up many sought-after applications, from real-time optical microscopy with super resolution, precise temperature and ambient reading and infrared light detection, to optical analog-to-digital conversion and quantum reading.

“No one has ever seen avalanche behavior like that in nanomaterials,” said James Schock, an associate professor of mechanical engineering who led the study, published today by Nature. “We have studied these new nanoparticles at the single nanoparticle level, allowing us to prove that avalanche-like behavior can occur in nanomaterials. This exquisite sensitivity can be incredibly transformative. For example, imagine if we can sense changes in our chemical environment, such as variations. in or the actual presence of molecular species. We may even be able to detect coronavirus and other diseases. “

Avalanche-forming processes – where a cascade of events is triggered by a series of small disturbances – are found in a wide range of phenomena outside snow slides, including champagne bubble bursting, nuclear explosions, laser bonding, neural networks and even financial crises. An avalanche is an extreme example of a nonlinear process in which a change in input or excitation results in a disproportionate – often disproportionately large – change in the output signal. Large volumes of material are usually required to efficiently generate nonlinear optical signals, as has been the case with avalanches of photons.

In optics, a photon avalanche is the process by which the absorption in a single crystal of a photon results in the emission of many. The researchers used a photon avalanche in specialized lasers, where the uptake of photons caused a chain reaction of optical events that ultimately led to efficient generation.

It is especially important for researchers that the absorption of only one photon leads not only to a large number of emitted photons, but also to a surprising property: the emitted photons are “converted upwards”, each with a higher energy (blue color) than a single absorbed one. photon. Scientists can use wavelengths in the infrared region of the optical spectrum to create large amounts of higher-energy photons, which are much better at inducing desired chemical changes – such as killing cancer cells – at target sites deep in the tissue wherever avalanche-like nanoparticles are located.

The behavior of photon avalanches (PA) aroused considerable interest more than 40 years ago, when researchers realized that its extreme nonlinearity could widely affect many technologies, from efficient conversion lasers to photonics, optical sensors, and night vision devices. The behavior of PA is similar to that of a transistor in electronics, where a small change in the input voltage leads to a large change in the output current, providing the gain needed to operate almost all electronic devices. PA allows some materials to function essentially as optical transistors.

PA has been almost exclusively studied in lanthanide (Ln) -based materials due to their unique optical properties, which allow them to store optical energy for relatively long periods of time. However, achieving PA in Ln systems is difficult – it requires interaction between many Ln ions, while moderating pathways of loss and thus being limited to bulk materials and aggregates, often at low temperatures.

These limitations have brought fundamental research and the use of PA to a niche role in photon science and have led researchers to focus almost exclusively in the last decade on other mechanisms for transformation in the development of materials, despite the unsurpassed advantages of PA.

In this new study, Schook and his international team of collaborators, including the Bruce Cohen and Emory Chan groups (Molecular Foundry, Lawrence Berkeley National Laboratory), Arthur Bednarkevich (Polish Academy of Sciences) and Jung Doug Soo (Korean Research Institute) of Chemical Technology and Sungkyunkwan University) have shown that by implementing some key innovations in nanoparticle design such as selected lanthanide content and species, they can successfully synthesize new 20nm nanocrystals that demonstrate photon maneuverability and its exceptional nonlinearity.

The team observed that the nonlinear optical response in these avalanche-like nanoparticles scaled as the 26th power of the incident light intensity – a 10% change in the incident light caused more than 1000% change in the emitted light. This nonlinearity far exceeds the responses previously reported in lanthanide nanocrystals. This exceptional reaction means that avalanche-like nanoparticles (ANPs) show great promise as sensors, as a small change in the local environment can cause particles to emit 100-10,000 times brighter. The researchers also found that this giant nonlinear response in ANP allows for deep optical wavelength imaging (such as ANPs are used as fluorescent probes or contrast agents) using only simple scanning confocal microscopy.

Shine on: Avalanche nanoparticles break down barriers to image cells in real time

Left: Experimental PASSI (photon avalanche single-beam images with super resolution) images of thulium-doped avalanche nanoparticles separated by 300 nanometers. Right: PASSI simulations of the same material. Credit: Berkeley Laboratory and Columbia University

“ANPs allow us to beat the diffraction limit for optical microscopy with a significant margin, and they do so essentially for free because of their steep nonlinear behavior,” explains Schuck.

Lead author Changwan Lee, a PhD student in the Schuck group, added: “The ultimate nonlinearity in an ANP makes the conventional confocal microscope the latest super-resolution imaging system.”

Now Schuck and his team are working on how to use this unprecedented nonlinear behavior to detect changes in the environment, such as fluctuations in temperature, pressure, humidity, with a sensitivity that is not yet achievable.

“We are very excited about our findings,” says Shuk. “We expect them to lead to all sorts of revolutionary new applications in sensors, images and light detection. They may also be critical in future optical data processing chips, with ANP providing an amplifier-like response and a small single-fingerprint spatial footprint. electronic circuit transistor. “

The study is titled “Giant Nonlinear Optical Reactions of Photon Avalanche Nanoparticles.”

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More information:
Giant nonlinear optical reactions of avalanche nanoparticles, Nature (2021). DOI: 10.1038 / s41586-020-03092-9, www.nature.com/articles/s41586-020-03092-9

Provided by Columbia University University School of Engineering and Applied Sciences

Quote: Engineers first observe avalanches in nanoparticles (2021, January 13) extracted on January 13, 2021 from https://phys.org/news/2021-01-avalanches-nanoparticles.html

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