Making x-ray detectors and medical imaging more sensitive and safer using bismuth oxyiodide

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"... have discovered that a solar cell material – bismuth oxyiodide (BiOI) – is capable of detecting X-ray dose rates over 250 times lower than the current best performing detectors used commercially. This has the potential to make medical imaging safer, and open up new opportunities in non-invasive diagnostics, such as X-ray video techniques. ... BiOI is nontoxic, stable in air, and can be grown cost-effectively and at scale. ...
The researchers developed and patented a method to grow high-quality single crystals of BiOI using a scalable vapour-based approach. The low defect density in these crystals led to stable and ultra-low dark currents, which was critical to substantially improve the sensitivity and detection limit of this material to X-rays. ..."

From the abstract:

"Detecting low dose rates of X-rays is critical for making safer radiology instruments, but is limited by the absorber materials available. Here, we develop bismuth oxyiodide (BiOI) single crystals into effective X-ray detectors. BiOI features complex lattice dynamics, owing to the ionic character of the lattice and weak van der Waals interactions between layers. Through use of ultrafast spectroscopy, first-principles computations and detailed optical and structural characterisation, we show that photoexcited charge-carriers in BiOI couple to intralayer breathing phonon modes, forming large polarons, thus enabling longer drift lengths for the photoexcited carriers than would be expected if self-trapping occurred. This, combined with the low and stable dark currents and high linear X-ray attenuation coefficients, leads to strong detector performance. High sensitivities reaching 1.1  × 103 μC Gyair−1 cm−2 are achieved, and the lowest dose rate directly measured by the detectors was 22 nGyair s−1. The photophysical principles discussed herein offer new design avenues for novel materials with heavy elements and low-dimensional electronic structures for (opto)electronic applications."

Sustainable solar cell material shown to be highly promising for medical imaging | University of Cambridge Using X-rays to see inside the human body has revolutionised non-invasive medical diagnostics. However, the dose of X-rays required for imaging is far higher than background levels, due to the poor performance of the detector materials currently available. This can cause harm to patients, and in some cases even cancer.

Sustainable solar cell material shown to be highly promising for medical imaging

Layered BiOI single crystals capable of detecting low dose rates of X-rays (open access)

Photograph of BiOI single crystal, along with the structure of each layer.