Microstructure and Optical Properties of BaF$_2$ Transparent Ceramics Fabricated by Air Pre-sintering and Hot Isostatic Pressing

BaF$_2$ scintillation ceramics feature a rapid temporal response, high fast-component light yield, and a short X-ray attenuation length, making them a promising material for ultrafast X-ray imaging. In this work, BaF$_2$ nanopowder was co-precipitated from Ba(NO$_3$)$_2$ and KF$\cdot$2H$_2$O, consolidated by 600-750$^{\circ}$C air pre-sintering, and post-treated by hot isostatic pressing (HIP). The ceramics obtained under various process parameters allowed us to investigate temperature-dependent changes in microstructure, transmittance, and scintillation properties, including X-ray-excited luminescence (XEL), decay kinetics, and light yield. It was found that air pre-sintered compacts are porous, with relative density reaching a maximum at 700$^{\circ}$C. In addition, HIP eliminated most of the pores, leaving only residual intragranular pores. Both in-line transmittance and scintillation properties correlated strongly with increasing air pre-sintering temperature. The optimized BaF$_2$ ceramic achieves an in-line transmittance (1mm thick) of 57.6% and 40.6% at 800nm and 220nm, respectively, with a fast component of 16.8% and a light yield of 2655ph/MeV. High-temperature thermoluminescence suggests that a deep trap with considerable intensity may be responsible for the reduced light yield in the ceramic sample.