Nanostructured flexible radiation sensors

Abstract

Flexible scintillating radiation detectors have gained increasing attention in the scientific community in the last decade. They represent a fast and easy way for monitoring the impinging radiation in real time and acquire the dose released in medical treatments, like cancer radio- or proton-therapy sessions. Flexible linear-chain polysiloxane detectors offer the possibility to overcome geometrical limitations, they possess superior optical transparency and flexibility, and can be obtained with contained production costs and times, making them highly competitive with respect to traditional single-crystals and plastics. Unlike phenyl-containing siloxanes, linear polysiloxanes does not show direct interaction with the impinging radiation, therefore they can be used just as matrices for hosting luminescent materials, such as nanocrystals or nanopowders. Quantum dots (QDs) are nanocrystals showing quantum confinement effects, with an incredible light yield, a tunable emission wavelength and a fast decay lifetime. For these reasons, they are worth being incorporated in siloxane-based scintillators as primary dyes, without the need of complex ternary systems. Part of this thesis analyzes the effects of ionizing radiation on the luminescence and temporal response of QD-loaded polysiloxanes for radiation detection and monitoring, with special focus on real-time measurements under proton beam. Another possibility is to embed luminescent nanopowders, such as zinc oxide (ZnO) and reduced zinc oxide (ZnO:Zn). The Zn-rich form shows a remarked green luminescence, with increasing light yield as a function of the reduction degree, i.e. zinc content. In view of the above, this thesis reports the advances on polysiloxanes loaded with ZnO and ZnO:Zn phosphors. The core of the thesis is devoted to the progresses in ZnO production and treatment for the realization of multi-layered flexible scintillators. A special focus is putted on a novel production route based on atmospheric pressure plasma (APPJ), that allows for the co-deposition of ZnO-loaded plasma polymers and for the doping via liquid precursor solution.