Resonant excited UV luminescence of the Gd3+ centres in borate glasses, co-doped with Gd and Ag

The Li2B4O7:Gd, CaB4O7:Gd, LiCaBO3:Gd, and Li2B4O7:Gd, Ag glasses of high optical quality, obtained by standard technology, have been investigated by electron paramagnetic resonance (EPR) and optical spectroscopy at room temperature. The Gd impurity was added in the raw materials as Gd2O3 oxide in amounts 0.5 and 1.0 mol.%. The Ag impurity was introduced into the Li2B4O7 composition as AgNO3 and as highly dispersed metallic Ag in amount 2.0 mol.%. In all Gd-doped glasses was observed typical for glasses EPR U-spectrum of the Gd3+ (S-8(7/2), 4f(7)) ions. In the Gd-doped glasses upon the 273 rim excitation was observed weak UV emission line at 311 nm that is attributed to the P-6(7/2)-> S-8(7/2) intraconfiguration 4f - 4f transition of the Gd3+ ions. In the Li2B4O7:Gd, Ag glass has been observed significant (similar to 100 times) increasing of peak intensity of the Gd3+ emission line at 311 nm in comparison with this line in CaB4O7:Gd glass. In luminescence excitation spectra of the CaB4O7:Gd and Li2B4O7:Gd, Ag glasses are observed characteristic groups of lines corresponding to the S-8(7/2) -> I-6(J), D-6(J) transitions of the Gd3+ ions. Significant increasing of the Gd3+ emission line at 311 nm in the Li2B4O7:Gd, Ag glass is explained by energy transfer from Ag+ (4d(10)) to Gd3+ (4f(7)) upon 273 rim excitation that is resonant for 4d(10)-> 4d(9) 5s(1) (S-1(0) -> D-1(2)) and S-8(7/2) -> I-6(J) transitions of the Ag+ and Gd3+ ions. Luminescence kinetics of the Gd3+ and Ag+ centres was investigated and analysed. Obtained results show that the borate glasses, co-activated by Gd3+ and Ag+, can be promising materials for effective UVB light sources for biomedical applications.