X-ray imaging is indispensable in medical diagnostics and material characterisation. To generate an image, a detector converts X-rays that pass through the object into electrical signals. Higher detector sensitivity enables lower radiation doses, which is particularly important in medical applications.

Currently used X-ray detectors consist of inorganic compounds of elements with medium to high atomic numbers. In recent years, inorganic perovskite compounds have also been tested as X-ray detectors with very good results.

Inspired by pervoskite materials

Now, a team led by X-ray detector expert Prof. Olena Maslyanchuk at HZB has demonstrated that two new Bismuth-based organic-inorganic hybrid materials can be used for highly efficient X-ray detection. The two bismuth-based materials explored in this work, [(CH₃CH₂)₃S]₆Bi₈I₃₀ and [(CH₃CH₂)₃S]AgBiI₅, were inspired by the emergence of halide perovskites in opto-electronic devices and were first explored by Dr. Allan Starkholm during his Ph.D. thesis work at the Royal Institute of Technology Stockholm, Sweden.

'The high atomic numbers, suitable band gaps and unique structural features make them ideal for X-ray detection,' says Starkholm: 'They contain stable sulfonium cations instead of the traditionally used hygroscopic ammonium cations that are promising for long term stability.'

Environmentally friendly manufacturing process

In collaboration with BAM expert Franziska Emmerling, a particularly environmentally friendly manufacturing process was used: ball milling. This produces polycrystalline powders that are then pressed into dense pellets. These procedures are also established in industry.

Up to 50 times more sensitive

In collaboration with the team of Dr. Felix Lang at Potsdam University the novel materials were evaluated for their use in X-ray detectors. 'The results show that they perform better than current commercial detectors, even over long periods of time,' says Starkholm. 'In fact, they demonstrate sensitivities up to two orders of magnitude higher than commercial materials like amorphous selenium or CdZnTe -- and can detect X-ray doses nearly 50 times lower,' says Starkholm.

In addition to extensive analysis in the laboratory, the team also studied the samples at the KMC-3 XPP beamline at BESSY II. The detectors maintained a stable response during pulsed X-ray irradiation under high-intensity photon flux, with no measurable degradation in performance observed post-exposure, highlighting the robustness of the detector materials.

Outlook to technology transfer

'We have shown that these entirely new bismuth-based materials are excellent candidates for X-ray detection. Our results highlight exciting opportunities to expand hybrid materials research at HZB beyond photovoltaics, both within and beyond the perovskite field. More sensitive X-ray detectors would allow to significantly reduce radiation exposure during X-ray imaging,' says Olena Maslyanchuk.

Technology transfer is the next step. 'There are so many exciting companies in Adlershof that we could work together with to optimise the development of such X-ray detectors,' says Starkholm.

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