Oxyhalide Glass Ceramics Containing Eu-Doped Calcium Fluoride Crystals Evaluated as X-ray Conversion Screens for...

Indirect flat panel detectors (I-FPDs) are commonly employed in digital radiography. A scintillating glass-based material, acting as a secondary X-ray conversion screen incorporated into a bidirectional I-FPD as a substrate for the photodiodes and thin film transistors (TFTs) may lead to improved detective quantum efficiency, especially at higher X-ray energies, by capturing otherwise undetected X-rays. This study examines the effectiveness of oxyhalide glass ceramics doped with europium as an X-ray conversion screen. In particular, the ability to control the precipitation of light-scattering CaF₂ crystallites to prevent "light trapping" is investigated. A series of 4 samples, with varying amounts of CaF₂ precursor material, doped with europium, was synthesized. The X-ray excited luminescence spectra showed that the detected light was mostly due to an Eu³⁺ emission, not CaF₂:Eu²⁺, and matched the quantum efficiency curve of amorphous silicon photodiodes well. The authors found the precipitation of CaF₂ could be controlled through sample composition and heat treatment protocol. The presence of CaF₂ crystallites reduced the effects of "light trapping" for the samples and increased the detected X-ray excited emission; this increase was greater than 100% for one of the samples. With optimization, these materials could serve as scintillating substrates in bidirectional I-FPDs.