Doping MOFs leads to red, blue emission

A new technique that employs a nanoporous material to efficiently identify neutrons could provide a more effective and less costly way for homeland security inspectors to detect radiation in cargo and baggage. Current neutron detection methods are expensive and technically…

A new technique that employs a nanoporous material to efficiently identify neutrons could provide a more effective and less costly way for homeland security inspectors to detect radiation in cargo and baggage.

Current neutron detection methods are expensive and technically challenging because of the difficulty in distinguishing neutrons from ubiquitous background gamma rays. In addition, traditional radiation detection techniques are limited in terms of speed and sensitivity, which are crucial elements for dynamic scenarios such as border crossings and nuclear treaty verification.

The new method, developed at Sandia National Laboratories, can monitor the color of light emissions, which could offer a screening process that is easier and more reliable than measuring the rate of light emissions. Called spectral shape discrimination (SSD), the technique takes advantage of a new class of nanoporous materials known as metallorganic frameworks (MOFs). By adding a doping agent to an MOF, the scientists discovered, the material emits red and blue light when it interacts with high-energy particles emanated from nuclear or radiological materials.

Team member Patrick Doty hypothesized that this discovery could be applied to radiation detection. The trick, he said, is to add just the right amount of dopant so that both the scavenged light and the fluorescence from the excited MOF itself are emitted. With this arrangement, the ratio of the intensities at the two wavelengths is a function of the type of high-energy particle interacting with the material.

“That’s the critical thing,” Doty said. “SSD allows one particle type to be distinguished from another on the basis of the color of the emitted light.”

Because the ratio of neutrons to gamma rays is so low, the threshold at which current detectors can see neutrons is fairly high. Sandia calculations suggest that the threshold for detecting neutrons produced by fissionable material could be substantially lowered using the new technique.

Improvements must be made before the technology moves into the marketplace, but Sandia is currently seeking commercial partners to license the technology.

photonics.com