Light Extraction Enhancement In Scintillation Crystals Using Thin Film Coatings

In gamma detectors based on scintillation crystals, light extraction efficiency is limited due to total internal reflection and Fresnel losses. Typically, reflective coatings such as ESR films are utilized to improve the light collection; however, the coating thickness limits the maximum achievable detector packing-fraction. In this paper, we propose a novel approach based on the combination of optimized dielectric mirrors and anti-reflection (AR) film coatings to enhance light extraction from scintillators. BGO and LYSO are used as reference scintillators and custom coatings were designed, by considering the scintillators' emission spectra and refractive indexes. The coatings are also fabricated by means of plasma-enhanced chemical vapor deposition (PECVD), which allows for fast-deposition, high reproducibility, cost-efficiency, large area coverage, and low deposition temperature. The thickness of the fabricated reflective coating is less than 2 mu m; subsequently, it enables a higher packing-fraction in pixelated submillimeter crystals arrays for preclinical PET detectors. Extensive experimentation has been carried out in order to compare the obtained results to state-of-the-art light-extraction methods.