Gradient Index Nanostructures for Enhanced Scintillation Light Extraction

Scintillators coupled to photomultiplier tubes or silicon photomultipliers are the most common detectors for X- ray/gamma ray detection, and recent years have seen the development of many excellent scintillator materials, used for the detection, measurement and imaging of ionizing radiation. However, due to the high refractive indices of these scintillators, techniques currently used for coupling scintillators to photodetectors are not efficient, and hence the excellent timing and high light output properties of such scintillators are not fully utilized. New means of maximizing the light transfer from the scintillator to the detector are, therefore, needed. In recent years, several different approaches have been investigated to increase the light extraction from scintillators, but none of them provide a cost-effective, scalable solution. To date, the highest extraction efficiency has been demonstrated using photonic crystals fabricated by electron beam lithography, which is a complex and slow process that is limited to very small areas, making it impractically expensive to use. To address this issue, we propose to use subwavelength gradient-index (GRIN) nanostructures that will rival the performance of photonic crystals, but will use a process that is scalable, fast, reproducible, and cheap, and can be implemented on both planar and non-planar curved surfaces on a manufacturing scale. The Phase I goal is to develop subwavelength GRIN nanostructures that provide an adiabatic transition in the RI from the scintillator to the photodetector. Because of the graded index profile, the proposed GRIN nanostructures will provide broadband, omnidirectional improvements in the transmission at the dielectric interface. These nanostructures will be imprinted in custom-developed, but low-cost, high-RI polymers with optical transmission and reliability optimized for the scintillator of choice. The Phase I effort will focus on reliability, performance, and cost of the proposed technology, and will develop methods to quantify enhancements in extraction efficiency and robustness of the GRIN nanostructure coatings.