Results of Photonic Crystal Enhanced Light Extraction on Heavy Inorganic Scintillators

Abstract

A major challenge for future particle physics experiments and nuclear medicine imaging applications will be the improvement of energy and time resolution of the detector systems. Both parameters are strongly correlated with the number of photoelectrons which can be registered after a particle has deposited its energy in the scintillator. One problem in heavy scintillating materials is that a large fraction of the light produced inside the bulk material is trapped inside the crystal due to total internal reflection. Recent developments in the area of nanophotonics show that those limitations can be overcome by introducing a photonic crystal (PhC) slab at the outcoupling surface of the scintillator. Photonic crystals are optical materials which can affect the propagation of light in multiple ways. In this work, the PhC is used for the extraction of photons which are otherwise reflected within the scintillator. Our simulations show light output improvements for a wide range of scintillating materials due to light scattering effects of the photonic grating. In the practical part of the work we show how we were producing first samples of PhC slabs on top of different scintillators to confirm the simulation results by measurements. Through the deposition of an auxiliary layer of silicon nitride and the adaptation of the standard electron beam lithography (EBL) parameters we could successfully produce several PhC slabs on top of 1.2 mm × 2.6 mm × 5 mm lutetium oxyorthosilicate (LSO) scintillators. In the characterization process we show a 30-60% light yield improvement of the different PhC designs when compared to an unstructured reference scintillator, which is also in close accordance with our simulation results.