Tl₂GdCl₅ (Ce³⁺): A New Efficient Scintillator for X-and γ -Ray Detection

We are in the process of developing novel thallium-based inorganic halide compounds for X- and γ -ray radiation detections. In this paper, novel cerium-activated single crystals of Tl₂GdCl₅ are reported along with a pure Tl₂GdCl₅. The two-zone vertical Bridgman method is used to grow this scintillator from its melt. Luminescence studies are performed under ultraviolet and X-ray excitations at room temperature. All of the Ce-activated samples exhibit similar emission bands in the range of 350-430 nm, with a peak around 388 nm, attributed to the 5d → 4f radiative transition of the Ce³⁺ ion. In the pure sample, an intense luminescence band appeared owing to the presence of the Tl⁺ ion in the host lattice, along with the typical Gd³⁺ emission (310 nm). Scintillation properties, such as energy resolution, light yield, and decay time, are evaluated under the γ -ray excitation. The scintillation properties vary with the Ce³⁺-concentration. The best performances are obtained for the 5-mol% Ce-activated crystal, which, under a 662-keV γ -ray excitation, exhibited an energy resolution of 5% (full-width at half-maximum) and light yield of 53 000 ± 5300 ph/MeV. Fast scintillation decay components followed by slow components are observed for all grown samples. The measured scintillation properties of Tl₂GdCl₅, which has high density and effective Z-number, reveal its large potentials as a radiation detector in medical imaging techniques.