Crystal growth and luminescence properties of Li2B4O7 single crystals doped with Ce, In, Ni, Cu and Ti ions

Li2B4O7 (LBO) is considered to be one of the useful materials for neutron detection because it contains Li and B, which possess large neutron capture cross-section isotopes. In the present study, we report crystal growth of LBO doped with Ce, In, Ni, Cu and Ti and some studies on their luminescent properties. Crystals were grown by the Bridgman method using Pt crucibles from the mixture of LBO with 0.5 wt% of In2O3, NiO, CuO and TiO2. CeO2 was added at 0.1, 1.0 and 2.0 wt% and the crystals were grown in one experiment. Though the crystals doped with Ce were not transparent except some small areas, the compound showed strong emission at 375 nm for two excitation peaks at 270 and 320 nm. The dopant Ce has not entered well into LBO and the transparent area of the crystal did not show any emission. The crystals grown with In2O3 and TiO2 also had lot of segregation with little transparency. The crystals grown with NiO and CuO were found to be highly transparent and clear except some area. The transmittance measured at clear area showed short wavelength cut-off at about 220 nm for the case of NiO doping and at about 200 nm for the case of CuO doping (the cut-off for pure LBO is 167 nm). There were absorption peaks at 440, 500 and 560 nm for Ni-doped LBO and at 240, 255 and 310 nm for Cu doping. Among these two crystals, Cu-doped LBO showed intense emission at 360 nm for the excitation at 245 nm.