Luminescence mechanism in doubly Gd, Nd-codoped fluoride crystals for VUV scintillators

The Nd-doped, Gd-doped and doubly Nd, Gd-codoped BaLu1.2Y0.8F8 (BaLuYF) and LuF3 single crystals were grown by a micro-pulling-down method. Their photoluminescence, radioluminescence and alpha-ray-excited pulse-height spectra were studied in the vacuum-ultra-violet (VUV) region to confirm their possible application as fast VUV scintillators. Complementary photoluminescence measurements in the ultra-violet/visible spectral region were performed as well. The possibility of scintillation performance improvement by Gd codoping was tested. The overall scintillation efficiency of BaLuYF:Nd1% was comparable to that of the LaF3:Nd8% reference sample and only slight improvement was observed after Gd1% codoping. The positive effect of Gd codoping was confirmed for higher dopant concentrations. This was explained by an energy transfer from the high-energy Gd3+ 4f 2G(0)7/2 level to the Nd3+ 5d state. On the other hand, pulse-height spectra showed degradation of the light yield under alpha-ray excitation, which was explained by introduction of slow components due to Gd codoping. On the other hand, no positive effect of Gd codoping was found for the overall scintillation efficiency of Nd-doped LuF3, despite the same energy transfer process was confirmed. Slight improvement of the light yield under alpha-ray excitation was confirmed.