Nonlinear luminescent nanocrystals are poised to enable faster and more energy-efficient data processing and artificial intelligence (AI) because of their superpower of “switching” from bright to dark states, which looks extremely promising for optical computing.
Scientists from Lawrence Berkeley National Laboratory, Columbia University, and the Autonomous University of Madrid are exploring luminescent nanocrystals (a.k.a. photon avalanching nanoparticles) because of their extreme nonlinear light emission properties, which means they emit light at an intensity that can be greatly increased via a tiny boost of laser intensity.
“My work with nanocrystals was initially inspired by their biomedical potential,” says Artiom Skripka, now an assistant chemistry professor at Oregon State University. “I’m still fascinated by the idea of using luminescent nanocrystals to locate and treat diseases, but I’ve become more interested in understanding the fundamental optical properties of various nanocrystals—regardless of their intended use.”
Nanocrystals and optical bistability
The team is working with nanocrystals made from inorganic materials—potassium, chlorine, and lead—and doped with lanthanide ions, which are elements found on the second to last line of the periodic table. These potassium lead chloride (KPb2Cl5) nanocrystals don’t interact with light, but they do enable lanthanide ions to interact with light signals more efficiently.
“Lanthanide ions have many available energy states that allow them to absorb and emit light across a broad spectral range— from ultraviolet to infrared,” explains Skripka. “These ions can also interact with each other by exchanging energy acquired from laser excitation.”
Introducing certain lanthanide ions in large quantities to the nanocrystals allows them to “all interact with each other as one big network, which may give rise to unintuitive phenomena,” Skripka says.
Intrinsic optical bistability arises precisely because of such interactions. “Energy exchange between neighboring lanthanide ions—neodymium, in our case—allows nanocrystals to switch on and off abruptly and to emit light at excitation intensities lower than were needed to switch them on,” says Skripka.
The team’s nanocrystals range between 10 and 100 nm in size, which enables their dense packing when envisioning miniaturized optical devices. “This allows optical techniques to compete with semiconductor electronics and possibly execute certain tasks more efficiently,” Skripka says. “As with other exotic phenomena that might be observed within bulk materials or predicted via simulations, having control over optical bistability at the nanoscale makes it so much more useful. For the first time, we have a robust and scalable nanomaterial that can act as a binary optical switch or a tiny memory unit.”
Skripka points out that it’s always important to keep an open mind with research. “You can sometimes be surprised and discover something unexpected,” he says. “Our work set us on the path of exploring how optical bistability within neodymium-doped nanocrystals arises and its potential usefulness. Both experimentally and numerically, we demonstrated that bistability within these nanocrystals differs from previous reports. It’s an all-optical process that can be harnessed, controlled, and exploited to store information or toggle light outputs at the nanoscale—similar to the way a transistor toggles electrical signals.”
Nonlinear processes at the nanoscale
When Skripka first observed the incredibly abrupt switching between the bright and dark states of luminescent nanocrystals, he was excited to see what may be one of the most nonlinear processes at the nanoscale. “But measuring bistability, which is luminescence hysteresis, left me in disbelief,” he says. “The first thing I did was realign my optical setup because I wanted to ensure our equipment was functioning properly and that I hadn’t measured an artifact—and it wasn’t.”
There are, however, a few material issues to resolve. “We reported optical bistability within certain materials with exceptionally low thermal vibrations but they’re lead-based, which isn’t ideal,” Skripka says. “We’re actively working on this by exploring different materials that have comparable physical properties but don’t involve heavy metals.”
Skripka and colleagues would also like to observe optical bistability at higher temperatures—preferably at room temperature. “Multiple material solutions are required to progress optical bistability at the nanoscale to ensure its applications,” he says.
Optical computing and memory applications ahead
The main applications for the bistable luminescent nanocrystals are optical computing and memory. “These nanomaterials may become the cornerstone of general-purpose optical computing within 10, 15, or so years,” says Skripka. “One can dream, right? But we believe there are opportunities to use these nanocrystals for imaging and sensing applications beyond computing, which further motivates our research on these materials.”
This work was carried out at the Molecular Foundry at Lawrence Berkeley National Lab, while Skripka was a postdoc. “Last fall, I joined Oregon State University as an assistant professor and am now building my group and facilities to advance research on optically bistable nanocrystals,” he says. “We hope that our group and other groups will be able to make significant advancements within this field. We’ve only scratched the surface, and there is so much more to do.”
FURTHER READING
A. Skripka et al., Nat. Photon., 19, 212–218 (2025); https://doi.org/10.1038/s41566-024-01577-x.
A. Skripka and E. Chan, ChemRxiv (2025); doi:10.26434/chemrxiv-2024-70qxn-v2.
Sally Cole Johnson | Editor in Chief
Sally Cole Johnson, Laser Focus World’s editor in chief, is a science and technology journalist who specializes in physics and semiconductors. She wrote for the American Institute of Physics for more than 15 years, complexity for the Santa Fe Institute, and theoretical physics and neuroscience for the Kavli Foundation.