Photo-luminescence properties of Cu and Ag doped Li2B4O7 single crystals at low temperatures

UV excited photo luminescence from Li2B4O7:Cu and Li2B4O7:Cu, Ag single crystals has been investigated in the temperature range from 77 K to 300 K. An excitation band having a doublet structure at 240 nm and 262 nm was observed for the emission at 370 nm that corresponds to 1A1g→1Eg and 1A1g→1T2g crystal field components of the 3d10→3d94s1 transition of Cu+. The relative intensity of these components and their temperature dependence provide a measure of the off-center displacement of the Cu+ ground state in the crystal lattice site. The co-doped Ag plays a role of a sensitizer when doped with Cu and increases the overall emission as the emission between Ag states lies in the excitation region of Cu states. The 370 nm emission in both the crystals slightly decreases with temperature; however a sudden increase in the intensity around 264 K was observed.