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

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.