2-D Nanoscale Coating for Optimized Light Extraction from Inorganic Scintillators

Gamma spectroscopy is used for various applications, including nuclear nonproliferation and safeguards, isotope identification, astronomy, and medical applications. Inorganic scintillators are widely used for gamma spectroscopy because of their energy resolution at room temperature, lower cost, and relatively high light yields. However, inorganic scintillators typically have a high refractive index, which results in substantial light losses due to total internal reflection. In this work, 2-D periodic nanostructure photonic crystals are used to provide an optical coupling between the scintillator and photosensor to mitigate the original light loss via constructive interference. Such photonic crystal geometry needs to be optimized for the specific scintillator material and photosensor. This optimization is performed using two simulation codes: Geant4 and OptiFDTD, to account for macroscale and nanoscale light transport, respectively. This coupled simulation tool has been used to find the optimized photonic crystal geometry for a LYSO scintillator coupled with Si3N4 photonic crystals. Preliminary simulation results with 2-D photonic crystals show more than 62% improvement in light transmission for the first pass of light through the photonic crystals. Reflections at the LYSO interfaces have not been simulated. Future work will incorporate reflections at all interfaces, more complex geometries, as well as optimized 3-D photonic crystals. The optimized 2-D geometries are being manufactured in the lab and characterized with various gamma sources to assess the resulting improvements in energy resolution.