Fabrication and optical properties of BaF₂ scintillation ceramics for ultrafast imaging applications

To address the high repetition rates and pileup effects in the development of future ultrafast imagers, stringent requirements have been proposed for scintillators. Novel ultrafast scintillators featuring short X-ray attenuation lengths and low levels of slow components are required. BaF₂ scintillation ceramics combine core advantages, such as fast response characteristics, high light yield within the first nanosecond, and short X-ray attenuation length, demonstrating significant potential for ultrafast imaging applications. In this study, BaF₂ powder was synthesized via a chemical co-precipitation method using barium nitrate (Ba(NO₃)₂) and potassium fluoride dihydrate (KF·2H₂O) as raw materials₂, and BaF₂ scintillation ceramics were prepared using hot-pressing technology. The effects of hot-pressing temperature (550-650 ℃) on the microstructure, optical transmittance, and X-ray excited luminescence (XEL) intensity of BaF₂ scintillation ceramics were investigated. The results indicate that as the hot-pressing temperature increases, the pore density in the ceramics initially decreases and then increases. Similarly, the in-line transmittance and XEL intensity of the BaF₂ ceramics first increase and then decrease with rising hot-pressing temperature. BaF₂ scintillation ceramics prepared by hot-pressing (1 mm thickness) at 600 ℃ for 2 h under 50 MPa exhibited an in-line transmittance of 48.2% at 800 nm, the highest fast luminescence XEL intensity, and significant suppression of the slow component. Compared with BaF₂ single crystals, the slow decay component in the ceramic samples was effectively suppressed; the fast decay component accounted for 10.6% (compared to 6.2% in single crystals), and the light yield was 4021 ph/MeV. Furthermore, the mechanism underlying the suppression of the slow decay component in the ceramics was investigated. The study confirmed the presence of fast self-trapped exciton quenching centers within the BaF₂ scintillation ceramics, evidenced by a lower intensity of the 109 K thermoluminescence peak compared to that of the single crystal sample. This phenomenon leads to a reduced proportion of the slow decay component in the ceramics. This work elucidates how hot-pressing temperature affects the overall performance of the ceramics and, through comparison with single crystals, reveals the mechanism suppressing the slow luminescence of BaF₂ ceramics.