Barium fluoride (BaF ₂ ) crystal has a fast scintillation light peaked at 195 and 220 nm with a sub-ns decay time. This ultrafast scintillation promises a wide application in an area where extreme fast timing is important, such as future high-energy physics experiments, gigahertz hard X-ray imaging, and time-of-flight positron emission tomography. BaF ₂ crystal, however, has also a slow scintillation component peaked at 310 nm with a decay time of about 600 ns, which causes pileup. Suppression of the slow scintillation component by selective doping, such as Ce, La, Tm, and Y, was discussed 20 years ago. In this paper, we report suppression of the slow component in BaF ₂ crystals by yttrium doping. Single crystals with 1 at% Y doping were grown by vacuum Bridgman technique at the Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, China. Their radioluminescence, optical transmittance, light output, fast/slow ratio, decay kinetics, and light response uniformity were measured. The results show that 1 at% Y doping suppresses the slow scintillation component in BaF ₂ crystals by a factor of 6, while the fast component remains unaffected.

Due to its ultrafast cross-luminescence, the BaF ₂ crystals with a subnanosecond decay time are promising for high-reputation radiation detection. However, there is a slow scintillation component with a decay time of about 600 ns in the crystal, which induces a pile-up effect. The Y doping in the crystal was confirmed to be effective in slow component suppression. In this investigation, the fast/total (F/T) light yield (LY) ratios and fast component LY of BaF ₂ :Y crystals with various Y concentrations were investigated by the fast sampling technique. It was demonstrated that Y doping not only suppresses the slow component but also weakens the fast component. A good negative correlation was observed between the F/T LY ratios and fast component LY of BaF ₂ :Y crystals, indicating that it was impossible to obtain the BaF ₂ :Y crystal with a high F/T LY ratio and a high fast component LY at the same time. The influence of wrapping materials on the F/T LY ratio was also investigated. The result illustrates that both the undoped and Y-doped BaF ₂ crystals without wrapping materials show the best F/T LY ratio, indicating that the tradeoff between LY and F/T LY ratio is needed in the applications.