Luminescence and scintillation properties of scintillators based on orthorhombic and monoclinic BaLu₂F₈ single crystals

The rare-earth-doped orthorhombic BaLu₂F₈ vacuum-ultra-violet scintillator crystals have been studied. The fast emission around 185 nm with a decay time of several nanoseconds was due to the allowed 5d-4f transition of the Nd³⁺ ion. The high temperature phase BaLu₂ F₈ orthorhombic crystals have been prepared by micro-pulling-down method. Unfortunately, no 5d-4f emission (neither from Nd³⁺ nor from Tm³⁺) was observed in the crystals under excitation by ionizing radiation at all. This was explained by preferential energy transfer from the host to the lattice defect states. Further improvement of the scintillation efficiency by facilitating the energy transfer from the host matrix to the Nd³⁺ luminescence center by Tm³⁺ -codoping was attempted. The energy transfer from the Tm³⁺ ions to the Nd³⁺ ones has been proved, however, no improvement of the overall scintillation efficiency was observed.