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Improved photon efficient cathodes with applications in biological luminescence (IMPECABLE)

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Extending biological luminescence applications

Aiming at developing better sensors in the red/NIR region, the use of structured photomultiplier tube windows to enhance quantum efficiency has been extensively investigated.


Long wavelengths (in the region of 750nm) luminescence can find useful applications in in vivo and in vitro diagnostics. There are several spectral differences between healthy and diseased tissue in the non-invasive monitoring of Alzheimer degeneration and in fluorescence changes in early stage of various forms of cancer. Additionally, pharmaceuticals, as well as non-radioactive assays and gene sequencing need better red detectors. Urged by this the IMPECABLE project focused on improving photocathodes for extending their applications in the field of biological and medical luminescence. More specifically, the key aim was to enhance the performance of low cost trialkali photocathodes for photomultiplier, imaging and intensifier tubes. Currently, the semi-transparency of these photocathodes at the longer wavelengths seriously affects their performance. By redesigning the device interface using ridge and narrow angled cone, structures absorption could be significantly improved. Expected improvement target values in quantum efficiency are from x2 for UV /blue light to nearly x15 to 30 in the red/NIR region with possible extension of operation for longer wavelengths. Part of the project work involved the fabrication of a range of structures on the interior of standard photomultiplier tubes for exploring their impact on quantum efficiency. Aided by two popular production processes, namely the sol-gel and the laser ablation, the quantum efficiencies of the structured cathodes were compared against those of flat windows. Although both methods resulted in significant increases in the cathode's quantum efficiency, the laser-ablation method was not found commercially viable for production. Incorporation of sol-gel windows into standard products is expected after resolving issues related to silica sealing in glass photomultiplier tubes.

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