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Engineers are observing avalanches in nanoparticles for the first time

Columbia engineers first observed avalanches in nanoparticles

An illustration of the chain reaction process underlying the photon-avalanche mechanism Columbia Engineering scientists have realized in their nanoparticles. In this process, the absorption of a single low-energy photon triggers a chain reaction of energy transfers and additional absorption events, resulting in many highly excited ions in the nanoparticle, which then release their energy into the intense emission of many higher energy photons. Credit: Mikołaj Łukaszewicz / Polish Academy of Sciences

Researchers at Columbia Engineering report today that they have developed the first nanomaterial that demonstrates “photon avalanching”, a process that is unmatched in the combination of extreme non-linear optical behavior and efficiency. The realization of photon avalanching in nanoparticle form opens up a range of in-demand applications, from real-time super-resolution optical microscopy, accurate temperature and environmental sensing and infrared light detection to optical analog-to-digital conversion and quantum sensing.

“No one has seen avalanche behavior like this in nanomaterials before,” said James Schuck, an associate professor of mechanical engineering who led the study published today by Nature. “We studied these new nanoparticles at the level of nanoparticles, so we could prove that avalanche behavior can occur in nanomaterials. This exquisite sensitivity can be incredibly transformative. Imagine, for example, whether we could notice changes in our chemical environment, as variations in or the actual presence of molecular species. We may even be able to detect coronavirus and other diseases. “

Avalanche processes – where a cascade of events are triggered by a series of small disturbances – are found in a wide range of phenomena in addition to snow-slides, including the popping of champagne bubbles, nuclear explosions, lasing, neural networks and even financial crises. Avalanche is an extreme example of a non-linear process in which a change in input or excitation leads to a disproportionate – often disproportionately large – change in the output signal. Large amounts of material are usually required for efficient generation of non-linear optical signals, and this had also been the case for photon valance until now.

In optics, photon avalanching is the process by which the absorption in a crystal of a single photon results in the emission of many. Researchers have used photon avalanches in specialized lasers, where photon absorption triggers a chain reaction of optical events that ultimately leads to efficient lasing.

Of particular attention to researchers is that the absorption of only a single photon not only leads to a large number of emitted photons, but also to a surprising property: the emitted photons are “upconverted”, each higher energy (bluer in color) than the single absorbed photon. Scientists can use wavelengths in the infrared region of the optical spectrum to create large amounts of higher-energy photons that are much better at inducing desired chemical changes – such as killing cancer cells – at targeted locations deep within tissues, anywhere avalanches the nanoparticles are located.

Photon avalanching (PA) gained significant interest more than 40 years ago, when scientists recognized that its extreme nonlinearity could greatly affect a variety of technologies, from efficient up-converting lasers to photonics, optical sensors, and night vision. PA behavior is similar to a transistor in electronics, where a small change in an input voltage results in a large change in the output current, providing the necessary amplification for the operation of almost all electronic devices. PA allows certain materials to essentially act as optical transistors.

PAs have been studied almost exclusively in materials based on lanthanide (Ln) due to their unique optical properties that allow them to store optical energy for relatively long periods of time. However, it has been difficult to obtain PA in Ln systems – it requires cooperative interactions between many Ln ions, while also moderating loss paths and has thus been limited to bulk materials and aggregates, often at low temperatures.

These limitations have referred the basic study and use of PA to a niche role in photonic science and have led researchers to focus almost exclusively over the last decade on other upconversion mechanisms in material development despite the unmatched benefits that PA offers. .

In this new study, Schuck and his international team of collaborators, including groups Bruce Cohen and Emory Chan (The Molecular Foundry, Lawrence Berkeley National Lab), Artur Bednarkiewicz (Polish Academy of Sciences), and Yung Doug Suh (Korea Research Institute) of Chemical Technology and Sungkyunkwan University), showed that by implementing some key nanoparticle design innovations such as selected lanthanide contents and species, they were able to successfully synthesize new 20 nm nanocrystals that demonstrate photon valance and its extreme nonlinearity.

The team observed that the non-linear optical response in these avalanche nanoparticles scales as the 26th effect of the incident light intensity – a 10% change in incident light causes more than a 1000% change in emitted light. This nonlinearity far exceeds the responses previously reported in nanocrystals of lanthanide. This extraordinary reaction means that avalanche nanoparticles (ANPs) show great promise as sensors, as a small change in the local environment can lead to the particles emitting 100-10,000 times more light. The researchers also found that this gigantic non-linear response in ANPs enables deep optical image processing during wavelength (with the ANPs used as luminescent probes or contrast agents) using only simple scanning confocal microscopy.

Shine on: Avalanching nanoparticles break barriers to real-time imaging cells

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

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

The study’s lead author Changhwan Lee, who is a Ph.D. students in Schuck’s group add: “The extreme non-linearity of a single ANP transforms a conventional confocal microscope into the latest super-resolution imaging system.”

Schuck and his team are now working on how to use this unprecedented non-linear behavior to detect changes in the environment, such as fluctuations in temperature, pressure, humidity, with a sensitivity that has not yet been possible.

“We are very excited about our findings,” Schuck says. “We expect that they will lead to all kinds of revolutionary new applications in sensing, imaging and light detection. They may also prove critical in future optical information processing chips, where ANPs provide the amplifier-like response and small spatial footprint typical of a single transistor in an electronics circuit. “

The study is entitled “Fighting Nonlinear Optical Reactions from Photon Navalanching Nanoparticles.”

New ‘dual-resonant method’ in 2-D materials can spur progress in photonics

More information:
Fighting non-linear optical reactions from photon-avalanche nanoparticles, Nature (2021). DOI: 10.1038 / s41586-020-03092-9, www.nature.com/articles/s41586-020-03092-9

Provided by Columbia University School of Engineering and Applied Science

Citation: Engineers Observe Avalanche Nanoparticles for the First Time (2021, January 13) Retrieved January 13, 2021 from https://phys.org/news/2021-01-avalanches-nanoparticles.html

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