Photonic crystals: enhancing the light output of scintillation based detectors

Abstract

One of the problems in heavy scintillating materials is related to their high index of refraction. As a consequence, most of the scintillation light produced in the bulk material is trapped inside the crystal due to total internal reflection. These limitations can be overcome by means of Photonic crystals (PhCs). PhCs are nano structured optical materials which can affect the propagation of light in multiple ways. In recent years PhCs contributed to major technological developments in the field of semiconductor lasers, light emitting diodes and photovoltaic applications. In this thesis the capabilities of photonic crystal slabs are investigated with the aim to improve the performance of heavy inorganic scintillators. To study the combination of scintillators and PhCs we used a Monte-Carlo program to simulate the light propagation inside a scintillator and a rigorous coupled wave analysis (RCWA) framework to analyse the optical PhC properties. The simulations show light output improvements of a wide range of scintillating materials due to light scattering effects of the PhC slabs. To prove the simulation results several PhC samples have been produced on top of 1.2 x 2 x 5mm 3 LSO (cerium-doped Lutetium Oxyorthosilicate, Lu2SiO5:Ce3+) scintillators. The nanostructured PhC pattern was made by using electron beam lithography and reactive ion etching (RIE). As a main result, the PhC samples show a 30-60% light output improvement when compared to unstructured reference crystals which is in close accordance with our simulation results.