Scintillation properties of Nd³⁺, Tm³⁺, and Er ³⁺ doped LuF₃ scintillators in the vacuum ultra violet region

In order to develop novel vacuum ultra violet (VUV) emitting scintillators, we grew Nd 0.5%, Tm 0.5%, and Er 0.5% doped LuF₃ scintillators by the μ-pulling down method, because LuF₃ has a very wide band gap and Nd³⁺, Tm³⁺, and Er³⁺ luminescence centers show fast and intense 5d4f emission in VUV region. Transmittance and X-ray induced radioluminescence were studied in these three samples using our original spectrometer made by Bunkou-Keiki company. In the VUV region, transmittance of 2060% was achieved for all the samples. The emission peaks appeared at approximately 180, 165, and 164 nm for Nd³⁺, Tm³⁺, and Er³⁺ doped LuF₃, respectively. Using PMT R8778 (Hamamatsu), we measured their light yields under ²⁴¹Am α-ray excitation. Compared with Nd:LaF₃ scintillator, which has 33 photoelectrons/5.5 MeV α, Nd:LuF₃ and Tm:LuF₃ showed 900±90 and 170±20 ph/5.5 MeV-α, respectively. Only for the Nd doped one, we can detect ¹³⁷Cs 662 keV γ-ray photoabsorption peak and the light yield of 1200±120 ph/MeV was measured. We also investigated their decay time profiles by picosecond pulse X-ray equipped streak camera, and the main decay component of Nd:LuF₃ turned out to be 7.63 ns.