Radioluminescence Properties of Tb-Doped PbF2 Crystals Obtained By Spontaneous Melt Crystallization

Radiation detectors equipped with scintillators are used in a variety of fields such as medicine, security, and radiation protection, and as there is no material that satisfies all required characteristics, research is still being conducted to find materials with higher performance. In addition, single crystal materials are widely used as scintillators, but the production methods such as the Czochralski method and Bridgman–Stockbarger method require a long period of time for crystal growth. Our group is aiming to develop new high-performance scintillators by a simple preparation method. We are studying spontaneous melt crystallization as a simple preparation method of samples. In this simple method, raw materials are melted and solidified in a crucible without moving a crucible or a seed crystal. It is possible to obtain transparent materials in the case of highly symmetrical crystalline materials by this method. So far, we have investigated CaF 2 -based and BaF 2 -based materials. In this study, we focused on PbF 2 , which contains heavy elements. Materials containing heavy elements are particularly important target because they have a high probability of interaction with X-rays and gamma rays. Tb 3+ ions were selected as the luminescent center, which can show highly efficient emissions. The samples were prepared by the procedure described below. High-purity powders of PbF 2 and TbF 3 were used as raw materials, and after being weighed at a predetermined molar ratio, they were filled into a carbon crucible, placed in an electric furnace equipped with a vacuum chamber, and heated to approximately 300℃ in vacuum. Then, the raw material powders were melted at 850℃ in an Ar and CF 4 mixed gas atmosphere, and the temperature was decreased to room temperature. The XRD patterns of obtained crystals were ascribed to that of β-PbF 2 . The X-ray induced scintillation spectra of the obtained samples were measured, and radioluminescence associated with 4f-4f transitions of Tb 3+ ions was observed in each sample.