A study of the sensitization of Gd/sup 3+/ luminescence by Pb/sup 2+/ ions

The possibilities of the sensitization of the Gd/sup 3+/ luminescence by Pb/sup 2+/ ions has been studied in Tb/sup 3+/ -activated gadolinium compounds (GdBO/sub 3/ and GdB/sub 3/O/sub 6/) and alkaline-earth gadolinium compounds [Ba/sub 3-x/Gd/sub 1+x/(PO/sub 4/)/sub 3/(SiO/sub 4/)/sub x/ with x = 0 and 1, and Sr/sub 2/Gd/sub 8/(SiO/sub 4/)/sub 6/O/sub 2/]. Incomplete or even absence of Pb/sup 2+/ to Gd/sup 3+/ energy transfer was observed for GdBO/sub 3/, GdB/sub 3/O/sub 6/, and Ba/sub 3-x/Gd/sub 1+x/(PO/sub 4/)/sub 3-x/(SiO/sub 4/)/sub x/. In these compounds, the Pb/sup 2+/ luminescence has a large Stokes shift. The result is that Pb/sup 2+/ ions are out of resonance with the Gd/sup 3+/ ions for energy transfer. This can be partly compensated by direct Pb/sup 2+/ to Tb/sup 3+/ energy transfer. This transfer has a critical distance of about 6A. Efficient energy transfer from Pb/sup 2+/ to Tb/sup 3+/ was observed only for Sr/sub 2/Gd/sub 8/(SiO/sub 4/)/sub 6/O/sub 2/, but even there this holds only for Pb/sup 2-/ ions on the crystallographic 4f site of the apatite structure. The luminescence of Pb/sup 2+/ ions on the other cation site (6h) has a large Stokes shift. This ion is coordinated to an O/sup 2-/ ion, whose bonding strength is not saturated. This type of coordination results in large Stokes shifts. Evidence from the literature is presented