Nanophotonic patterns make scintillators shine brighter

24 Mar 2022

More light: a transmission electron microscope image of a grid that is normally used to support specimens. The scintillator in the square region bounded by the white dashed lines has a nanophotonic array of holes, enhancing the light output of this area. (Courtesy: Charles Roques-Carmes, Nicholas Rivera, Marin Soljacic, Steven Johnson, and John Joannopoulos, et al)

The efficiency of some radiation detectors can be boosted by adding nanostructure arrays to scintillator materials. Charles Roques-Carmes and colleagues at the Massachusetts Institute of Technology have shown how the modifications increase the amount of light emitted by the scintillators by a factor of ten when the materials are exposed to either X-rays or high-energy electrons.

Scintillation occurs in a range of materials – solid, liquid and gas – when they are exposed to ionizing radiation. The radiation is absorbed by a scintillator’s atoms or molecules and some of the energy is re-emitted as light. The light can then be detected, allowing scintillators to be used as radiation detectors with applications including medical imaging, industrial quality control and particle physics experiments.

Researchers are always trying to develop better scintillators that produce more light when irradiated or have a shorter delay between the absorption of radiation and emission of light. Most studies so far have focused on developing new materials with brighter, faster, and more controlled scintillation – but this can be costly and time-consuming.

In their study, Roques-Carmes’ team took a simpler approach based on nanophotonics. They calculated that scintillation in materials can be enhanced by incorporating nanoscale features onto the surfaces of scintillating materials. The sizes of these features should be comparable to the wavelengths of the light that is emitted by the scintillators.

Unified theory

To explore this idea, the researchers first developed a unified theory of nanophotonic scintillators – which could predict from first principles how ionizing radiation interacts with the nanostructured surface any arbitrary material. Afterwards, they designed a method for integrating nanophotonic structures into existing scintillators. This could be done either by etching patterns onto the scintillator directly, or attaching a layer on top of the material, etched with an array of holes.

Roques-Carmes and colleagues then did a series of experiments that confirmed their calculations. They etched regular grids of circular holes onto the surfaces of two different types of scintillator – one that is used to detect X-rays and the other used to detect electrons. These holes were tens of nanometres deeps and had radii of about 200 nm.

In both scintillators the team measured a tenfold increase in light production in regions containing the nanostructures. Through further improvements, they hope that their generalized approach could lead to a new class of brighter, faster, and higher-resolution scintillators, with a hundredfold improvement on existing materials.

If achieved, this could lead to promising advances in a diverse array of applications: including higher-quality medical X-ray images that are produced using lower X-ray doses. This could significantly improve the safety of X-ray imaging, particularly for younger patients and those requiring routine screening. Elsewhere, the technique could lead to higher resolutions in particle detectors and electron microscopes, as well as faster and higher-quality inspections of manufactured parts.

The research is described in Science.

Sam Jarman is a science writer based in the UK.

from physicsworld.com   2/6/2022