Novel molecular design increases scintillator radiant emission by 1,300x

Scientists at the National University of Singapore (NUS) have developed a highly effective and general molecular design that can enhance radiative emissions in metal-organic scintillators by more than three orders of magnitude. This enhancement takes advantage of X-ray-induced triplet exciton recycling within the lanthanide metal complex.

Detection of ionizing radiation is important in various fields such as medical radiography, environmental monitoring, and astronomy. As a result, significant efforts have been devoted to developing luminescent materials that are responsive to X-rays.

However, current high-performance scintillators are almost limited to ceramic and perovskite materials and face problems such as complex manufacturing processes, environmental toxicity, self-absorption, and stability issues.

Organic phosphors are a promising alternative due to their flexibility and cost-effectiveness. However, the efficiency of X-ray detection is low due to the weak absorption of X-rays and the limited use of molecular triplet excitons.

Halogen-doped organic phosphors and thermally activated delayed fluorescent molecules have potential but require precise structural engineering, face absorption and reabsorption challenges, and have limited efficiency.

A research team led by Professor Liu Xiaogang from the NUS Department of Chemistry leveraged rare earth X-ray absorption and ligand-mediated triplet exciton collection to overcome these challenges and significantly improve the performance of molecular scintillators.

Effective capture of energy dissipated during secondary X-ray relaxation via organic ligands resulted in a remarkable 1,300-fold increase in radioemission compared to lanthanide salts.

This study reveals the role of triplet exciton recycling in determining scintillation efficiency and demonstrates that high photoluminescence quantum yield does not necessarily lead to high scintillation efficiency.

This research was conducted in collaboration with Professor Yiming Wu from Xiamen University, China, and Professor Xian Qin from Fujian Normal University, China.

The results of this research were published in the journal Nature Photonics.

Importantly, these organo-lanthanide compounds exhibit robust resistance to high-energy radiation and exhibit scintillation efficiencies that exceed well-known organic scintillators and inorganic LYSO:Ce crystals. Their performance was also comparable to that of CsI:Tl crystals.

The researchers demonstrated that by tuning the metal center and its coordinating ligands, full-spectrum X-ray scintillation spanning the ultraviolet to near-infrared range can be achieved. Moreover, their methodology allows fine-tuning of the emission lifetime in the range of 50 nanoseconds to 900 microseconds.

These organo-lanthanide scintillators exhibit significant Stokes shifts and have the advantage of being synthesized and processed in solution at room temperature. Furthermore, they exhibit excellent solubility, stability, and flexibility, allowing for molecular-level mixing for potential applications in high-resolution radiographic imaging and X-ray-mediated deep tissue radiotherapy.

Professor Liu said, “The recycling efficiency of triplet excitons is the key to improving scintillation performance. Shaping the future of usage.” X-ray quantum.

“The high stability of the radiated emission, large Stokes shift, and complete spectral tunability make organic lanthanide molecules a promising platform for scintillation applications.”