By offering dependable high-resolution imaging results and improving fabrication approaches, steady cheap organic-based materials can change X-Ray imaging. KAUST scientists have now developed a new method for designing and constructing such highly efficient scintillator materials for sensing X-Rays at minimal doses.
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A scintillator is a material that absorbs the energy and reemits a part of it as low-energy visible light when it is hit by high-energy ionizing radiation such as X-Rays. In several applications, from medical radiography to airport security scanners, scintillators are extensively employed for X-Ray imaging screens.
Nevertheless, the most prevalent scintillators are built of perovskite or ceramic materials, usually made under extreme conditions and can be plagued with poor stability with time upon exposure to air and light.
Organic-based scintillators have inherent advantages, such as low toxicity, high mechanical flexibility, low cost, and straightforward large-scale production. However, balancing the X-Ray absorption capability, exciton utilization efficiency and photoluminescence quantum yield of organic scintillators has proven challenging.
Jian-Xin Wang, King Abdullah University of Science and Technology
Wang worked on the project under the supervision of Omar Mohammed and his co-workers.
Until now, organic scintillator materials have been hindered using the short range of X-Ray frequencies, which can be naturally absorbed by them. Wang and colleagues, however, understood that X-Ray absorption needs to increase considerably with the increase in the incorporated elements’ atomic number.
Specifically, the team thought that adding heavy atoms to the scintillator material could solve this issue. Owing to the photoelectric effect, which is the emission of electrons upon excitation from radiation, X-Ray photons can interact with heavy atoms effectively.
We used a simple molecular engineering strategy to design novel organic scintillators. We began by introducing chlorine, bromine or iodine to thermally activated delayed fluorescence (TADF) chromophores. We then observed how these heavy atoms altered the efficiency and resolution of the resulting X-Ray images.
Jian-Xin Wang, King Abdullah University of Science and Technology
TADF chromophores are beneficial as they are in an excited quantum “triplet state” in the excitons’ form—which is the bound states of electrons and electron holes that are formed while absorption of a high-energy X-Ray photon takes place, “lifting an electron out of its hole.” While the chromophores absorb thermal energy, the triplet state transforms into a singlet state. Then, they can de-excite to the ground state and release light in a process known as delayed fluorescence.
“This means that, due to the minimized singlet-triplet energy gap, TADF chromophores can harness both the singlet and triplet excitons that are generated when they are exposed to X-Ray radiation,” added Wang.
This dramatically improves the exciton utilization efficiency of the scintillator, which in turn provides much higher X-Ray spatial imaging resolution and ultralow detection sensitivity.
Omar Mohammed, King Abdullah University of Science and Technology
The methodology of fabricating screens with scintillators doped using heavy atoms has shown to be efficient so far. One of the team’s scintillators, built with TADF-Br (bromine) chromophores, has surpassed the resolution of several reported organometallic and organic scintillation screens.
“These fabricated screens provide a powerful design approach and promising new alternative materials for making X-Ray imaging scintillators with outstanding sensitivity, low cost, and high stability,” stated Mohammed.
Currently, the team is developing a portable X-Ray sensor with their fabricated screen for high-resolution medical imaging, as well as health checks and dental examinations. The development of tiny wearable X-Ray devices could also be advanced through their design.
Journal References:
- Wang, J-X., et al. (2022) Heavy-atom engineering of thermally activated delayed fluorophores for high-performance X-ray imaging scintillators. Nature Photonics. doi.org/10.1038/s41566-022-01092-x
- Wang,J-X., et al. (2023) Triplet-triplet energy-transfer-based transparent X-ray imaging scintillators. Matter. doi.org/10.1016/j.matt.2022.09.031
Source: https://www.kaust.edu.sa/en