Nanocrystals have been made that can switch between glowing and darkness fast enough that they could be used in computing. Some of the ingredients used in the initial demonstration may impede widespread applications, but the findings are a significant advance down the long road to lower-energy IT as processing demand skyrockets.
So much solar power was installed last year that some experts expect world consumption of fossil fuels may have peaked. Those who disagree with this assessment point to rising energy consumption, particularly for AI and cryptocurrency mining. Instead of simply watching whether renewables can outrace rapidly rising demand, some researchers hope to find more energy-efficient ways of conducting the calculations on which these two energy hogs depend.
A new entrant in this race is doped nanocrystals, whose states of light and dark can represent ones and zeros for information storage. The nanocrystals belong to a class of materials known as optically bistable. That is, they can be in one of two states in terms of light emissions, reflections or transmissions depending on previous exposure, and either state is maintained for extensive periods unless something changes. Previous examples of optical bistability suffered from serious drawbacks, such as depending on temperature changes that make it hard to prevent interference between neighbors.
“Normally, luminescent materials give off light when they are excited by a laser and remain dark when they are not,” Dr Artiom Skripka of Oregon State University said in a statement. “In contrast, we were surprised to find that our nanocrystals live parallel lives. Under certain conditions, they show a peculiar behavior: They can be either bright or dark under exactly the same laser excitation wavelength and power.”
Schematic of how optically bistable crystals, as demonstrated in this study, can have information written or erased using laser illumination above or below certain levels .
Image credit: Artiom Skripka, OSU College of Science
Exposure to a laser above a certain power will make one of the crystals light up, and when illumination drops below a weaker threshold they turn off, but there’s a large zone in between where the previous state is maintained.
“If the crystals are dark to start with, we need a higher laser power to switch them on and observe emission, but once they emit, we can observe their emission at lower laser powers than we needed to switch them on initially,” Skripka continued. “It’s like riding a bike – to get it going, you have to push the pedals hard, but once it is in motion, you need less effort to keep it going. And their luminescence can be turned on and off really abruptly, as if by pushing a button.”
Photonics, which would replace electrons in computing with photons of light, has been an area of great research for decades. The potential benefits are enormous, starting with the vastly greater speed at which light travels.
However, making it work in practice has proven difficult. These crystals may provide a crucial component.
“Integrating photonic materials with intrinsic optical bistability could mean faster and more efficient data processors, enhancing machine learning algorithms and data analysis,” Skripka noted. “It could also mean more-efficient light-based devices of the type used in fields like telecommunications, medical imaging and environmental sensing.”
The crystals Skripka and colleagues demonstrated have a matrix with a formula of KPb2Cl5, which may alert some people to one potential problem. Society has finally gotten sick enough of the consequences of lead to try to replace the metal wherever possible, not by finding new applications. In an operating computer, the crystals shouldn’t be a problem, but their presence might make disposal of used machines an issue.
Furthermore, these crystals are not luminous until doped with neodymium 3+ ions. Neodymium is one of the so-called “rare earths” currently causing geopolitical jitters because the processing of their ores is dominated by China, which some people fear could cut off the access of countries it deems hostile.
The experiment was done on crystals cooled to almost -200 °C (-328 °F), which also offers some obvious practical problems.
“More research is necessary to address challenges such as scalability and integration with existing technologies before our discovery finds a home in practical applications,” Skripka said.
These drawbacks may be judged worth the energy savings. Ideally, now we know optical bistability is possible under much more attractive circumstances than previously achieved, further research will hopefully find preferable ways to do the same thing.
The study is published in Nature Photonics.
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