VUV and UV spectroscopy of ns2 ions co-doped with Tb3+ ion in Ln(BO2)3 (Ln=La, Gd)

Excitation spectra of some ns2 ions, In+, Sn2+, and Sb3+ (n=5), and Tl+ and Bi3+ (n=6), added to Ln(BO2)3:Tb3+(Ln=Sc,Y; La, Gd, Lu) have been measured in the range of 130-300 nm. For the Tl+ and Bi3+ ions in the La- and Gd-metaborates, the dipole strength ratios of the C band to the A band were checked semiquantitatively. A comparison of the spectra with and without these ns2 ions revealed that the overlap of the C band absorption in Tl+ or Bi3+ ions and host absorption due to polyborate anions yields an efficient energy transfer from these ions to Tb3+ ion. The estimated efficiency at 147 nm (8.43 eV) was about 95% for Gd(BO2)3:Bi,Tb and 130% for Gd(BO2)3:Tl,Tb, compared with that of commercial Zn2SiO4:Mn. These green phosphors are promising candidates for mercury-free fluorescent lamps.