Crystal growth and scintillation properties of selected fluoride crystals for VUV scintillators

Single crystals of orthorhombic and monoclinic BaLu₂F₈doped with Nd and Tm were grown by micro-pulling-down method. The monoclinic (low temperature modification) was grown using LiF flux, while the orthorhombic (high temperature modification) was grown with special hot-zone with shallow gradient and employing quenching process. Reasonable scintillation efficiency was achieved for the crystals of the former modification, while no rare-earth ion emission was observed in the latter due to preferential energy transfer to defects. The orthorhombic (low temperature) modification of ErF₃was grown using LiF flux and hot zone with steep gradient. Quite low scintillation efficiency was found for the Nd-doped sample due to energy migration over the Er³⁺levels. Possibility of using pure ErF₃as an infra-red scintillator is discussed.