Researchers at MIT have shown that scintillators, materials that emit light when bombarded with high-energy particles or x-rays, can be improved by at least tenfold, and potentially even a hundredfold, by modifying their surface to create nanoscale configurations such as arrays of wave-like ridges. The work has the potential to greatly reduce the amount of radiation needed to produce an image.
Often employed in medical or dental x-ray systems, scintillators convert incoming x-ray radiation into visible light that can then be captured using film or photosensors. They are also used in night-vision systems and in research settings, such as in particle detectors or electron microscopes.
While previous attempts at developing more efficient scintillators have focused on finding new materials that produce brighter or faster light emissions, the approach taken by the research team can, in principle, work with any of the existing materials. By creating patterns in scintillator materials at a length scale comparable to the wavelengths of the light being emitted, the team found that it was possible to dramatically change the material’s optical properties.
Researchers at MIT have shown how one could improve the efficiency of scintillators by at least tenfold by changing the material’s surface. This image shows a TEM grid on Scotch tape, with the right side showing the scene after it is corrected. Courtesy of MIT.
According to doctoral student Charles Roques-Carmes, to make what they’re calling “nanophotonic scintillators,” one can directly make patterns within the scintillators, or glue on another material that would have nanoscale holes.
“The specifics depend on the exact structure and material,” he said.
In this case, the team took a scintillator and made holes spaced apart by roughly one optical wavelength, or about 500 nm.
“The key to what we’re doing is a general theory and framework we have developed,” doctoral student Nicholas Rivera said. This allows the researchers to calculate the scintillation levels that would be produced by any arbitrary configuration of nanophotonic structures. The scintillation process itself involves a complex series of steps making it difficult to unravel. The framework the team developed involved integrating three different types of physics, Roques-Carmes said. Using this system, they have found a good match between their predictions and the results of their subsequent experiments.
The experiments showed a tenfold improvement in emission from the treated scintillator.
“So, this is something that might translate into applications for medical imaging, which are optical photon-starved, meaning the conversion of x-rays to optical light limits the image quality,” Roques-Carmes said.
He and his team believe that the work could open a new field of research in nanophotonics. “You can use a lot of the existing work and research that has been done in the field of nanophotonics to improve significantly on existing materials that scintillate,” he said.
MIT professor Marin Soljacic, who was not associated with the work, said that while the experiments demonstrated a tenfold improvement in emission, fine-tuning the design of the nanoscale could increase that to a hundredfold improvement. He and his team believe that there is a potential to improve it beyond that point as well. In other areas of nanophotonics, Soljacic said, the development of computational simulations has enabled rapid, substantial improvements, for example in the development of solar cells and LEDs. The new models this team developed for scintillating materials could facilitate similar leaps in this technology, he said.
According to Soljacic, nanophotonics grant a great deal of control over the behavior of light. “But until now, this promise, this ability to do this with scintillation was unreachable because modeling the scintillation was very challenging. Now, this work for the first time opens up this field of scintillation, fully opens it, for the application of nanophotonics techniques.”
More generally, the team believes that the combination of nanophotonic and scintillators might ultimately enable higher resolution, reduced x-ray dose, and energy-resolved x-ray imaging. Eli Yablonovitch, a professor of electrical engineering and computer sciences at the University of California, Berkeley, who was not associated with this research, also commented on the work. Yablonovitch highlighted the importance of new scintillator concepts in medical imaging and in basic research.
“After years of research on photonic crystals in optical communication and other fields, it’s long overdue that photonic crystals should be applied to scintillators, which are of great practical importance yet have been overlooked,” Yablonovitch said.
He noted that the concept has yet to be proven in a practical device.
The work was supported, in part, by the U.S. Army Research Office and the U.S. Army Research Laboratory through the Institute for Soldier Nanotechnologies; by the Air Force Office of Scientific Research; and by a Mathworks Engineering Fellowship.
The research was published in Science (www.doi.org/10.1126/science.abm9293).