On the role of the network modifier PbO in Sm3+-doped borate glasses

A series of Sm3+-doped lead borate glasses with a lead oxide (PbO) content varying from 20 mol% to 80 mol% and a samarium oxide (Sm2O3) content of 1 mol% is investigated. In addition to the network changes in the glass structure, the lead doping has a significant influence on the fluorescence properties of Sm3+ and on the tuneable intrinsic fluorescence of Pb2+ itself. The Pb2+ excitation band shifts monotonously to lower energies; its intensity is significantly reduced for a PbO content of 50 mol% and more. For a concentration of 30 mol%, the Pb2+ emission overlaps with the intense 6H5/2 to 6P5/2 Sm3+ excitation band enabling for radiative and non-radiative energy transfers. Lifetime measurements of excited Sm3+ show in all cases non-single exponential decay and were fitted by the Inokuti-Hirayama model indicating non-radiative dipole-dipole interaction between neighbouring Sm3+ ions.